diff options
Diffstat (limited to 'security/landlock')
| -rw-r--r-- | security/landlock/Kconfig | 21 | ||||
| -rw-r--r-- | security/landlock/Makefile | 4 | ||||
| -rw-r--r-- | security/landlock/common.h | 20 | ||||
| -rw-r--r-- | security/landlock/cred.c | 46 | ||||
| -rw-r--r-- | security/landlock/cred.h | 58 | ||||
| -rw-r--r-- | security/landlock/fs.c | 1205 | ||||
| -rw-r--r-- | security/landlock/fs.h | 71 | ||||
| -rw-r--r-- | security/landlock/limits.h | 27 | ||||
| -rw-r--r-- | security/landlock/object.c | 67 | ||||
| -rw-r--r-- | security/landlock/object.h | 91 | ||||
| -rw-r--r-- | security/landlock/ptrace.c | 120 | ||||
| -rw-r--r-- | security/landlock/ptrace.h | 14 | ||||
| -rw-r--r-- | security/landlock/ruleset.c | 475 | ||||
| -rw-r--r-- | security/landlock/ruleset.h | 180 | ||||
| -rw-r--r-- | security/landlock/setup.c | 40 | ||||
| -rw-r--r-- | security/landlock/setup.h | 18 | ||||
| -rw-r--r-- | security/landlock/syscalls.c | 456 |
17 files changed, 2913 insertions, 0 deletions
diff --git a/security/landlock/Kconfig b/security/landlock/Kconfig new file mode 100644 index 000000000..8e33c4e8f --- /dev/null +++ b/security/landlock/Kconfig @@ -0,0 +1,21 @@ +# SPDX-License-Identifier: GPL-2.0-only + +config SECURITY_LANDLOCK + bool "Landlock support" + depends on SECURITY && !ARCH_EPHEMERAL_INODES + select SECURITY_PATH + help + Landlock is a sandboxing mechanism that enables processes to restrict + themselves (and their future children) by gradually enforcing + tailored access control policies. A Landlock security policy is a + set of access rights (e.g. open a file in read-only, make a + directory, etc.) tied to a file hierarchy. Such policy can be + configured and enforced by any processes for themselves using the + dedicated system calls: landlock_create_ruleset(), + landlock_add_rule(), and landlock_restrict_self(). + + See Documentation/userspace-api/landlock.rst for further information. + + If you are unsure how to answer this question, answer N. Otherwise, + you should also prepend "landlock," to the content of CONFIG_LSM to + enable Landlock at boot time. diff --git a/security/landlock/Makefile b/security/landlock/Makefile new file mode 100644 index 000000000..7bbd2f413 --- /dev/null +++ b/security/landlock/Makefile @@ -0,0 +1,4 @@ +obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o + +landlock-y := setup.o syscalls.o object.o ruleset.o \ + cred.o ptrace.o fs.o diff --git a/security/landlock/common.h b/security/landlock/common.h new file mode 100644 index 000000000..5dc0fe157 --- /dev/null +++ b/security/landlock/common.h @@ -0,0 +1,20 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Landlock LSM - Common constants and helpers + * + * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net> + * Copyright © 2018-2020 ANSSI + */ + +#ifndef _SECURITY_LANDLOCK_COMMON_H +#define _SECURITY_LANDLOCK_COMMON_H + +#define LANDLOCK_NAME "landlock" + +#ifdef pr_fmt +#undef pr_fmt +#endif + +#define pr_fmt(fmt) LANDLOCK_NAME ": " fmt + +#endif /* _SECURITY_LANDLOCK_COMMON_H */ diff --git a/security/landlock/cred.c b/security/landlock/cred.c new file mode 100644 index 000000000..ec6c37f04 --- /dev/null +++ b/security/landlock/cred.c @@ -0,0 +1,46 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Landlock LSM - Credential hooks + * + * Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net> + * Copyright © 2018-2020 ANSSI + */ + +#include <linux/cred.h> +#include <linux/lsm_hooks.h> + +#include "common.h" +#include "cred.h" +#include "ruleset.h" +#include "setup.h" + +static int hook_cred_prepare(struct cred *const new, + const struct cred *const old, const gfp_t gfp) +{ + struct landlock_ruleset *const old_dom = landlock_cred(old)->domain; + + if (old_dom) { + landlock_get_ruleset(old_dom); + landlock_cred(new)->domain = old_dom; + } + return 0; +} + +static void hook_cred_free(struct cred *const cred) +{ + struct landlock_ruleset *const dom = landlock_cred(cred)->domain; + + if (dom) + landlock_put_ruleset_deferred(dom); +} + +static struct security_hook_list landlock_hooks[] __lsm_ro_after_init = { + LSM_HOOK_INIT(cred_prepare, hook_cred_prepare), + LSM_HOOK_INIT(cred_free, hook_cred_free), +}; + +__init void landlock_add_cred_hooks(void) +{ + security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks), + LANDLOCK_NAME); +} diff --git a/security/landlock/cred.h b/security/landlock/cred.h new file mode 100644 index 000000000..af89ab00e --- /dev/null +++ b/security/landlock/cred.h @@ -0,0 +1,58 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Landlock LSM - Credential hooks + * + * Copyright © 2019-2020 Mickaël Salaün <mic@digikod.net> + * Copyright © 2019-2020 ANSSI + */ + +#ifndef _SECURITY_LANDLOCK_CRED_H +#define _SECURITY_LANDLOCK_CRED_H + +#include <linux/cred.h> +#include <linux/init.h> +#include <linux/rcupdate.h> + +#include "ruleset.h" +#include "setup.h" + +struct landlock_cred_security { + struct landlock_ruleset *domain; +}; + +static inline struct landlock_cred_security * +landlock_cred(const struct cred *cred) +{ + return cred->security + landlock_blob_sizes.lbs_cred; +} + +static inline const struct landlock_ruleset *landlock_get_current_domain(void) +{ + return landlock_cred(current_cred())->domain; +} + +/* + * The call needs to come from an RCU read-side critical section. + */ +static inline const struct landlock_ruleset * +landlock_get_task_domain(const struct task_struct *const task) +{ + return landlock_cred(__task_cred(task))->domain; +} + +static inline bool landlocked(const struct task_struct *const task) +{ + bool has_dom; + + if (task == current) + return !!landlock_get_current_domain(); + + rcu_read_lock(); + has_dom = !!landlock_get_task_domain(task); + rcu_read_unlock(); + return has_dom; +} + +__init void landlock_add_cred_hooks(void); + +#endif /* _SECURITY_LANDLOCK_CRED_H */ diff --git a/security/landlock/fs.c b/security/landlock/fs.c new file mode 100644 index 000000000..64ed76654 --- /dev/null +++ b/security/landlock/fs.c @@ -0,0 +1,1205 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Landlock LSM - Filesystem management and hooks + * + * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net> + * Copyright © 2018-2020 ANSSI + * Copyright © 2021-2022 Microsoft Corporation + */ + +#include <linux/atomic.h> +#include <linux/bitops.h> +#include <linux/bits.h> +#include <linux/compiler_types.h> +#include <linux/dcache.h> +#include <linux/err.h> +#include <linux/fs.h> +#include <linux/init.h> +#include <linux/kernel.h> +#include <linux/limits.h> +#include <linux/list.h> +#include <linux/lsm_hooks.h> +#include <linux/mount.h> +#include <linux/namei.h> +#include <linux/path.h> +#include <linux/rcupdate.h> +#include <linux/spinlock.h> +#include <linux/stat.h> +#include <linux/types.h> +#include <linux/wait_bit.h> +#include <linux/workqueue.h> +#include <uapi/linux/landlock.h> + +#include "common.h" +#include "cred.h" +#include "fs.h" +#include "limits.h" +#include "object.h" +#include "ruleset.h" +#include "setup.h" + +/* Underlying object management */ + +static void release_inode(struct landlock_object *const object) + __releases(object->lock) +{ + struct inode *const inode = object->underobj; + struct super_block *sb; + + if (!inode) { + spin_unlock(&object->lock); + return; + } + + /* + * Protects against concurrent use by hook_sb_delete() of the reference + * to the underlying inode. + */ + object->underobj = NULL; + /* + * Makes sure that if the filesystem is concurrently unmounted, + * hook_sb_delete() will wait for us to finish iput(). + */ + sb = inode->i_sb; + atomic_long_inc(&landlock_superblock(sb)->inode_refs); + spin_unlock(&object->lock); + /* + * Because object->underobj was not NULL, hook_sb_delete() and + * get_inode_object() guarantee that it is safe to reset + * landlock_inode(inode)->object while it is not NULL. It is therefore + * not necessary to lock inode->i_lock. + */ + rcu_assign_pointer(landlock_inode(inode)->object, NULL); + /* + * Now, new rules can safely be tied to @inode with get_inode_object(). + */ + + iput(inode); + if (atomic_long_dec_and_test(&landlock_superblock(sb)->inode_refs)) + wake_up_var(&landlock_superblock(sb)->inode_refs); +} + +static const struct landlock_object_underops landlock_fs_underops = { + .release = release_inode +}; + +/* Ruleset management */ + +static struct landlock_object *get_inode_object(struct inode *const inode) +{ + struct landlock_object *object, *new_object; + struct landlock_inode_security *inode_sec = landlock_inode(inode); + + rcu_read_lock(); +retry: + object = rcu_dereference(inode_sec->object); + if (object) { + if (likely(refcount_inc_not_zero(&object->usage))) { + rcu_read_unlock(); + return object; + } + /* + * We are racing with release_inode(), the object is going + * away. Wait for release_inode(), then retry. + */ + spin_lock(&object->lock); + spin_unlock(&object->lock); + goto retry; + } + rcu_read_unlock(); + + /* + * If there is no object tied to @inode, then create a new one (without + * holding any locks). + */ + new_object = landlock_create_object(&landlock_fs_underops, inode); + if (IS_ERR(new_object)) + return new_object; + + /* + * Protects against concurrent calls to get_inode_object() or + * hook_sb_delete(). + */ + spin_lock(&inode->i_lock); + if (unlikely(rcu_access_pointer(inode_sec->object))) { + /* Someone else just created the object, bail out and retry. */ + spin_unlock(&inode->i_lock); + kfree(new_object); + + rcu_read_lock(); + goto retry; + } + + /* + * @inode will be released by hook_sb_delete() on its superblock + * shutdown, or by release_inode() when no more ruleset references the + * related object. + */ + ihold(inode); + rcu_assign_pointer(inode_sec->object, new_object); + spin_unlock(&inode->i_lock); + return new_object; +} + +/* All access rights that can be tied to files. */ +/* clang-format off */ +#define ACCESS_FILE ( \ + LANDLOCK_ACCESS_FS_EXECUTE | \ + LANDLOCK_ACCESS_FS_WRITE_FILE | \ + LANDLOCK_ACCESS_FS_READ_FILE) +/* clang-format on */ + +/* + * All access rights that are denied by default whether they are handled or not + * by a ruleset/layer. This must be ORed with all ruleset->fs_access_masks[] + * entries when we need to get the absolute handled access masks. + */ +/* clang-format off */ +#define ACCESS_INITIALLY_DENIED ( \ + LANDLOCK_ACCESS_FS_REFER) +/* clang-format on */ + +/* + * @path: Should have been checked by get_path_from_fd(). + */ +int landlock_append_fs_rule(struct landlock_ruleset *const ruleset, + const struct path *const path, + access_mask_t access_rights) +{ + int err; + struct landlock_object *object; + + /* Files only get access rights that make sense. */ + if (!d_is_dir(path->dentry) && + (access_rights | ACCESS_FILE) != ACCESS_FILE) + return -EINVAL; + if (WARN_ON_ONCE(ruleset->num_layers != 1)) + return -EINVAL; + + /* Transforms relative access rights to absolute ones. */ + access_rights |= + LANDLOCK_MASK_ACCESS_FS & + ~(ruleset->fs_access_masks[0] | ACCESS_INITIALLY_DENIED); + object = get_inode_object(d_backing_inode(path->dentry)); + if (IS_ERR(object)) + return PTR_ERR(object); + mutex_lock(&ruleset->lock); + err = landlock_insert_rule(ruleset, object, access_rights); + mutex_unlock(&ruleset->lock); + /* + * No need to check for an error because landlock_insert_rule() + * increments the refcount for the new object if needed. + */ + landlock_put_object(object); + return err; +} + +/* Access-control management */ + +/* + * The lifetime of the returned rule is tied to @domain. + * + * Returns NULL if no rule is found or if @dentry is negative. + */ +static inline const struct landlock_rule * +find_rule(const struct landlock_ruleset *const domain, + const struct dentry *const dentry) +{ + const struct landlock_rule *rule; + const struct inode *inode; + + /* Ignores nonexistent leafs. */ + if (d_is_negative(dentry)) + return NULL; + + inode = d_backing_inode(dentry); + rcu_read_lock(); + rule = landlock_find_rule( + domain, rcu_dereference(landlock_inode(inode)->object)); + rcu_read_unlock(); + return rule; +} + +/* + * @layer_masks is read and may be updated according to the access request and + * the matching rule. + * + * Returns true if the request is allowed (i.e. relevant layer masks for the + * request are empty). + */ +static inline bool +unmask_layers(const struct landlock_rule *const rule, + const access_mask_t access_request, + layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS]) +{ + size_t layer_level; + + if (!access_request || !layer_masks) + return true; + if (!rule) + return false; + + /* + * An access is granted if, for each policy layer, at least one rule + * encountered on the pathwalk grants the requested access, + * regardless of its position in the layer stack. We must then check + * the remaining layers for each inode, from the first added layer to + * the last one. When there is multiple requested accesses, for each + * policy layer, the full set of requested accesses may not be granted + * by only one rule, but by the union (binary OR) of multiple rules. + * E.g. /a/b <execute> + /a <read> => /a/b <execute + read> + */ + for (layer_level = 0; layer_level < rule->num_layers; layer_level++) { + const struct landlock_layer *const layer = + &rule->layers[layer_level]; + const layer_mask_t layer_bit = BIT_ULL(layer->level - 1); + const unsigned long access_req = access_request; + unsigned long access_bit; + bool is_empty; + + /* + * Records in @layer_masks which layer grants access to each + * requested access. + */ + is_empty = true; + for_each_set_bit(access_bit, &access_req, + ARRAY_SIZE(*layer_masks)) { + if (layer->access & BIT_ULL(access_bit)) + (*layer_masks)[access_bit] &= ~layer_bit; + is_empty = is_empty && !(*layer_masks)[access_bit]; + } + if (is_empty) + return true; + } + return false; +} + +/* + * Allows access to pseudo filesystems that will never be mountable (e.g. + * sockfs, pipefs), but can still be reachable through + * /proc/<pid>/fd/<file-descriptor> + */ +static inline bool is_nouser_or_private(const struct dentry *dentry) +{ + return (dentry->d_sb->s_flags & SB_NOUSER) || + (d_is_positive(dentry) && + unlikely(IS_PRIVATE(d_backing_inode(dentry)))); +} + +static inline access_mask_t +get_handled_accesses(const struct landlock_ruleset *const domain) +{ + access_mask_t access_dom = ACCESS_INITIALLY_DENIED; + size_t layer_level; + + for (layer_level = 0; layer_level < domain->num_layers; layer_level++) + access_dom |= domain->fs_access_masks[layer_level]; + return access_dom & LANDLOCK_MASK_ACCESS_FS; +} + +static inline access_mask_t +init_layer_masks(const struct landlock_ruleset *const domain, + const access_mask_t access_request, + layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS]) +{ + access_mask_t handled_accesses = 0; + size_t layer_level; + + memset(layer_masks, 0, sizeof(*layer_masks)); + /* An empty access request can happen because of O_WRONLY | O_RDWR. */ + if (!access_request) + return 0; + + /* Saves all handled accesses per layer. */ + for (layer_level = 0; layer_level < domain->num_layers; layer_level++) { + const unsigned long access_req = access_request; + unsigned long access_bit; + + for_each_set_bit(access_bit, &access_req, + ARRAY_SIZE(*layer_masks)) { + /* + * Artificially handles all initially denied by default + * access rights. + */ + if (BIT_ULL(access_bit) & + (domain->fs_access_masks[layer_level] | + ACCESS_INITIALLY_DENIED)) { + (*layer_masks)[access_bit] |= + BIT_ULL(layer_level); + handled_accesses |= BIT_ULL(access_bit); + } + } + } + return handled_accesses; +} + +/* + * Check that a destination file hierarchy has more restrictions than a source + * file hierarchy. This is only used for link and rename actions. + * + * @layer_masks_child2: Optional child masks. + */ +static inline bool no_more_access( + const layer_mask_t (*const layer_masks_parent1)[LANDLOCK_NUM_ACCESS_FS], + const layer_mask_t (*const layer_masks_child1)[LANDLOCK_NUM_ACCESS_FS], + const bool child1_is_directory, + const layer_mask_t (*const layer_masks_parent2)[LANDLOCK_NUM_ACCESS_FS], + const layer_mask_t (*const layer_masks_child2)[LANDLOCK_NUM_ACCESS_FS], + const bool child2_is_directory) +{ + unsigned long access_bit; + + for (access_bit = 0; access_bit < ARRAY_SIZE(*layer_masks_parent2); + access_bit++) { + /* Ignores accesses that only make sense for directories. */ + const bool is_file_access = + !!(BIT_ULL(access_bit) & ACCESS_FILE); + + if (child1_is_directory || is_file_access) { + /* + * Checks if the destination restrictions are a + * superset of the source ones (i.e. inherited access + * rights without child exceptions): + * restrictions(parent2) >= restrictions(child1) + */ + if ((((*layer_masks_parent1)[access_bit] & + (*layer_masks_child1)[access_bit]) | + (*layer_masks_parent2)[access_bit]) != + (*layer_masks_parent2)[access_bit]) + return false; + } + + if (!layer_masks_child2) + continue; + if (child2_is_directory || is_file_access) { + /* + * Checks inverted restrictions for RENAME_EXCHANGE: + * restrictions(parent1) >= restrictions(child2) + */ + if ((((*layer_masks_parent2)[access_bit] & + (*layer_masks_child2)[access_bit]) | + (*layer_masks_parent1)[access_bit]) != + (*layer_masks_parent1)[access_bit]) + return false; + } + } + return true; +} + +/* + * Removes @layer_masks accesses that are not requested. + * + * Returns true if the request is allowed, false otherwise. + */ +static inline bool +scope_to_request(const access_mask_t access_request, + layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS]) +{ + const unsigned long access_req = access_request; + unsigned long access_bit; + + if (WARN_ON_ONCE(!layer_masks)) + return true; + + for_each_clear_bit(access_bit, &access_req, ARRAY_SIZE(*layer_masks)) + (*layer_masks)[access_bit] = 0; + return !memchr_inv(layer_masks, 0, sizeof(*layer_masks)); +} + +/* + * Returns true if there is at least one access right different than + * LANDLOCK_ACCESS_FS_REFER. + */ +static inline bool +is_eacces(const layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS], + const access_mask_t access_request) +{ + unsigned long access_bit; + /* LANDLOCK_ACCESS_FS_REFER alone must return -EXDEV. */ + const unsigned long access_check = access_request & + ~LANDLOCK_ACCESS_FS_REFER; + + if (!layer_masks) + return false; + + for_each_set_bit(access_bit, &access_check, ARRAY_SIZE(*layer_masks)) { + if ((*layer_masks)[access_bit]) + return true; + } + return false; +} + +/** + * check_access_path_dual - Check accesses for requests with a common path + * + * @domain: Domain to check against. + * @path: File hierarchy to walk through. + * @access_request_parent1: Accesses to check, once @layer_masks_parent1 is + * equal to @layer_masks_parent2 (if any). This is tied to the unique + * requested path for most actions, or the source in case of a refer action + * (i.e. rename or link), or the source and destination in case of + * RENAME_EXCHANGE. + * @layer_masks_parent1: Pointer to a matrix of layer masks per access + * masks, identifying the layers that forbid a specific access. Bits from + * this matrix can be unset according to the @path walk. An empty matrix + * means that @domain allows all possible Landlock accesses (i.e. not only + * those identified by @access_request_parent1). This matrix can + * initially refer to domain layer masks and, when the accesses for the + * destination and source are the same, to requested layer masks. + * @dentry_child1: Dentry to the initial child of the parent1 path. This + * pointer must be NULL for non-refer actions (i.e. not link nor rename). + * @access_request_parent2: Similar to @access_request_parent1 but for a + * request involving a source and a destination. This refers to the + * destination, except in case of RENAME_EXCHANGE where it also refers to + * the source. Must be set to 0 when using a simple path request. + * @layer_masks_parent2: Similar to @layer_masks_parent1 but for a refer + * action. This must be NULL otherwise. + * @dentry_child2: Dentry to the initial child of the parent2 path. This + * pointer is only set for RENAME_EXCHANGE actions and must be NULL + * otherwise. + * + * This helper first checks that the destination has a superset of restrictions + * compared to the source (if any) for a common path. Because of + * RENAME_EXCHANGE actions, source and destinations may be swapped. It then + * checks that the collected accesses and the remaining ones are enough to + * allow the request. + * + * Returns: + * - 0 if the access request is granted; + * - -EACCES if it is denied because of access right other than + * LANDLOCK_ACCESS_FS_REFER; + * - -EXDEV if the renaming or linking would be a privileged escalation + * (according to each layered policies), or if LANDLOCK_ACCESS_FS_REFER is + * not allowed by the source or the destination. + */ +static int check_access_path_dual( + const struct landlock_ruleset *const domain, + const struct path *const path, + const access_mask_t access_request_parent1, + layer_mask_t (*const layer_masks_parent1)[LANDLOCK_NUM_ACCESS_FS], + const struct dentry *const dentry_child1, + const access_mask_t access_request_parent2, + layer_mask_t (*const layer_masks_parent2)[LANDLOCK_NUM_ACCESS_FS], + const struct dentry *const dentry_child2) +{ + bool allowed_parent1 = false, allowed_parent2 = false, is_dom_check, + child1_is_directory = true, child2_is_directory = true; + struct path walker_path; + access_mask_t access_masked_parent1, access_masked_parent2; + layer_mask_t _layer_masks_child1[LANDLOCK_NUM_ACCESS_FS], + _layer_masks_child2[LANDLOCK_NUM_ACCESS_FS]; + layer_mask_t(*layer_masks_child1)[LANDLOCK_NUM_ACCESS_FS] = NULL, + (*layer_masks_child2)[LANDLOCK_NUM_ACCESS_FS] = NULL; + + if (!access_request_parent1 && !access_request_parent2) + return 0; + if (WARN_ON_ONCE(!domain || !path)) + return 0; + if (is_nouser_or_private(path->dentry)) + return 0; + if (WARN_ON_ONCE(domain->num_layers < 1 || !layer_masks_parent1)) + return -EACCES; + + if (unlikely(layer_masks_parent2)) { + if (WARN_ON_ONCE(!dentry_child1)) + return -EACCES; + /* + * For a double request, first check for potential privilege + * escalation by looking at domain handled accesses (which are + * a superset of the meaningful requested accesses). + */ + access_masked_parent1 = access_masked_parent2 = + get_handled_accesses(domain); + is_dom_check = true; + } else { + if (WARN_ON_ONCE(dentry_child1 || dentry_child2)) + return -EACCES; + /* For a simple request, only check for requested accesses. */ + access_masked_parent1 = access_request_parent1; + access_masked_parent2 = access_request_parent2; + is_dom_check = false; + } + + if (unlikely(dentry_child1)) { + unmask_layers(find_rule(domain, dentry_child1), + init_layer_masks(domain, LANDLOCK_MASK_ACCESS_FS, + &_layer_masks_child1), + &_layer_masks_child1); + layer_masks_child1 = &_layer_masks_child1; + child1_is_directory = d_is_dir(dentry_child1); + } + if (unlikely(dentry_child2)) { + unmask_layers(find_rule(domain, dentry_child2), + init_layer_masks(domain, LANDLOCK_MASK_ACCESS_FS, + &_layer_masks_child2), + &_layer_masks_child2); + layer_masks_child2 = &_layer_masks_child2; + child2_is_directory = d_is_dir(dentry_child2); + } + + walker_path = *path; + path_get(&walker_path); + /* + * We need to walk through all the hierarchy to not miss any relevant + * restriction. + */ + while (true) { + struct dentry *parent_dentry; + const struct landlock_rule *rule; + + /* + * If at least all accesses allowed on the destination are + * already allowed on the source, respectively if there is at + * least as much as restrictions on the destination than on the + * source, then we can safely refer files from the source to + * the destination without risking a privilege escalation. + * This also applies in the case of RENAME_EXCHANGE, which + * implies checks on both direction. This is crucial for + * standalone multilayered security policies. Furthermore, + * this helps avoid policy writers to shoot themselves in the + * foot. + */ + if (unlikely(is_dom_check && + no_more_access( + layer_masks_parent1, layer_masks_child1, + child1_is_directory, layer_masks_parent2, + layer_masks_child2, + child2_is_directory))) { + allowed_parent1 = scope_to_request( + access_request_parent1, layer_masks_parent1); + allowed_parent2 = scope_to_request( + access_request_parent2, layer_masks_parent2); + + /* Stops when all accesses are granted. */ + if (allowed_parent1 && allowed_parent2) + break; + + /* + * Now, downgrades the remaining checks from domain + * handled accesses to requested accesses. + */ + is_dom_check = false; + access_masked_parent1 = access_request_parent1; + access_masked_parent2 = access_request_parent2; + } + + rule = find_rule(domain, walker_path.dentry); + allowed_parent1 = unmask_layers(rule, access_masked_parent1, + layer_masks_parent1); + allowed_parent2 = unmask_layers(rule, access_masked_parent2, + layer_masks_parent2); + + /* Stops when a rule from each layer grants access. */ + if (allowed_parent1 && allowed_parent2) + break; + +jump_up: + if (walker_path.dentry == walker_path.mnt->mnt_root) { + if (follow_up(&walker_path)) { + /* Ignores hidden mount points. */ + goto jump_up; + } else { + /* + * Stops at the real root. Denies access + * because not all layers have granted access. + */ + break; + } + } + if (unlikely(IS_ROOT(walker_path.dentry))) { + /* + * Stops at disconnected root directories. Only allows + * access to internal filesystems (e.g. nsfs, which is + * reachable through /proc/<pid>/ns/<namespace>). + */ + allowed_parent1 = allowed_parent2 = + !!(walker_path.mnt->mnt_flags & MNT_INTERNAL); + break; + } + parent_dentry = dget_parent(walker_path.dentry); + dput(walker_path.dentry); + walker_path.dentry = parent_dentry; + } + path_put(&walker_path); + + if (allowed_parent1 && allowed_parent2) + return 0; + + /* + * This prioritizes EACCES over EXDEV for all actions, including + * renames with RENAME_EXCHANGE. + */ + if (likely(is_eacces(layer_masks_parent1, access_request_parent1) || + is_eacces(layer_masks_parent2, access_request_parent2))) + return -EACCES; + + /* + * Gracefully forbids reparenting if the destination directory + * hierarchy is not a superset of restrictions of the source directory + * hierarchy, or if LANDLOCK_ACCESS_FS_REFER is not allowed by the + * source or the destination. + */ + return -EXDEV; +} + +static inline int check_access_path(const struct landlock_ruleset *const domain, + const struct path *const path, + access_mask_t access_request) +{ + layer_mask_t layer_masks[LANDLOCK_NUM_ACCESS_FS] = {}; + + access_request = init_layer_masks(domain, access_request, &layer_masks); + return check_access_path_dual(domain, path, access_request, + &layer_masks, NULL, 0, NULL, NULL); +} + +static inline int current_check_access_path(const struct path *const path, + const access_mask_t access_request) +{ + const struct landlock_ruleset *const dom = + landlock_get_current_domain(); + + if (!dom) + return 0; + return check_access_path(dom, path, access_request); +} + +static inline access_mask_t get_mode_access(const umode_t mode) +{ + switch (mode & S_IFMT) { + case S_IFLNK: + return LANDLOCK_ACCESS_FS_MAKE_SYM; + case 0: + /* A zero mode translates to S_IFREG. */ + case S_IFREG: + return LANDLOCK_ACCESS_FS_MAKE_REG; + case S_IFDIR: + return LANDLOCK_ACCESS_FS_MAKE_DIR; + case S_IFCHR: + return LANDLOCK_ACCESS_FS_MAKE_CHAR; + case S_IFBLK: + return LANDLOCK_ACCESS_FS_MAKE_BLOCK; + case S_IFIFO: + return LANDLOCK_ACCESS_FS_MAKE_FIFO; + case S_IFSOCK: + return LANDLOCK_ACCESS_FS_MAKE_SOCK; + default: + WARN_ON_ONCE(1); + return 0; + } +} + +static inline access_mask_t maybe_remove(const struct dentry *const dentry) +{ + if (d_is_negative(dentry)) + return 0; + return d_is_dir(dentry) ? LANDLOCK_ACCESS_FS_REMOVE_DIR : + LANDLOCK_ACCESS_FS_REMOVE_FILE; +} + +/** + * collect_domain_accesses - Walk through a file path and collect accesses + * + * @domain: Domain to check against. + * @mnt_root: Last directory to check. + * @dir: Directory to start the walk from. + * @layer_masks_dom: Where to store the collected accesses. + * + * This helper is useful to begin a path walk from the @dir directory to a + * @mnt_root directory used as a mount point. This mount point is the common + * ancestor between the source and the destination of a renamed and linked + * file. While walking from @dir to @mnt_root, we record all the domain's + * allowed accesses in @layer_masks_dom. + * + * This is similar to check_access_path_dual() but much simpler because it only + * handles walking on the same mount point and only checks one set of accesses. + * + * Returns: + * - true if all the domain access rights are allowed for @dir; + * - false if the walk reached @mnt_root. + */ +static bool collect_domain_accesses( + const struct landlock_ruleset *const domain, + const struct dentry *const mnt_root, struct dentry *dir, + layer_mask_t (*const layer_masks_dom)[LANDLOCK_NUM_ACCESS_FS]) +{ + unsigned long access_dom; + bool ret = false; + + if (WARN_ON_ONCE(!domain || !mnt_root || !dir || !layer_masks_dom)) + return true; + if (is_nouser_or_private(dir)) + return true; + + access_dom = init_layer_masks(domain, LANDLOCK_MASK_ACCESS_FS, + layer_masks_dom); + + dget(dir); + while (true) { + struct dentry *parent_dentry; + + /* Gets all layers allowing all domain accesses. */ + if (unmask_layers(find_rule(domain, dir), access_dom, + layer_masks_dom)) { + /* + * Stops when all handled accesses are allowed by at + * least one rule in each layer. + */ + ret = true; + break; + } + + /* We should not reach a root other than @mnt_root. */ + if (dir == mnt_root || WARN_ON_ONCE(IS_ROOT(dir))) + break; + + parent_dentry = dget_parent(dir); + dput(dir); + dir = parent_dentry; + } + dput(dir); + return ret; +} + +/** + * current_check_refer_path - Check if a rename or link action is allowed + * + * @old_dentry: File or directory requested to be moved or linked. + * @new_dir: Destination parent directory. + * @new_dentry: Destination file or directory. + * @removable: Sets to true if it is a rename operation. + * @exchange: Sets to true if it is a rename operation with RENAME_EXCHANGE. + * + * Because of its unprivileged constraints, Landlock relies on file hierarchies + * (and not only inodes) to tie access rights to files. Being able to link or + * rename a file hierarchy brings some challenges. Indeed, moving or linking a + * file (i.e. creating a new reference to an inode) can have an impact on the + * actions allowed for a set of files if it would change its parent directory + * (i.e. reparenting). + * + * To avoid trivial access right bypasses, Landlock first checks if the file or + * directory requested to be moved would gain new access rights inherited from + * its new hierarchy. Before returning any error, Landlock then checks that + * the parent source hierarchy and the destination hierarchy would allow the + * link or rename action. If it is not the case, an error with EACCES is + * returned to inform user space that there is no way to remove or create the + * requested source file type. If it should be allowed but the new inherited + * access rights would be greater than the source access rights, then the + * kernel returns an error with EXDEV. Prioritizing EACCES over EXDEV enables + * user space to abort the whole operation if there is no way to do it, or to + * manually copy the source to the destination if this remains allowed, e.g. + * because file creation is allowed on the destination directory but not direct + * linking. + * + * To achieve this goal, the kernel needs to compare two file hierarchies: the + * one identifying the source file or directory (including itself), and the + * destination one. This can be seen as a multilayer partial ordering problem. + * The kernel walks through these paths and collects in a matrix the access + * rights that are denied per layer. These matrices are then compared to see + * if the destination one has more (or the same) restrictions as the source + * one. If this is the case, the requested action will not return EXDEV, which + * doesn't mean the action is allowed. The parent hierarchy of the source + * (i.e. parent directory), and the destination hierarchy must also be checked + * to verify that they explicitly allow such action (i.e. referencing, + * creation and potentially removal rights). The kernel implementation is then + * required to rely on potentially four matrices of access rights: one for the + * source file or directory (i.e. the child), a potentially other one for the + * other source/destination (in case of RENAME_EXCHANGE), one for the source + * parent hierarchy and a last one for the destination hierarchy. These + * ephemeral matrices take some space on the stack, which limits the number of + * layers to a deemed reasonable number: 16. + * + * Returns: + * - 0 if access is allowed; + * - -EXDEV if @old_dentry would inherit new access rights from @new_dir; + * - -EACCES if file removal or creation is denied. + */ +static int current_check_refer_path(struct dentry *const old_dentry, + const struct path *const new_dir, + struct dentry *const new_dentry, + const bool removable, const bool exchange) +{ + const struct landlock_ruleset *const dom = + landlock_get_current_domain(); + bool allow_parent1, allow_parent2; + access_mask_t access_request_parent1, access_request_parent2; + struct path mnt_dir; + layer_mask_t layer_masks_parent1[LANDLOCK_NUM_ACCESS_FS], + layer_masks_parent2[LANDLOCK_NUM_ACCESS_FS]; + + if (!dom) + return 0; + if (WARN_ON_ONCE(dom->num_layers < 1)) + return -EACCES; + if (unlikely(d_is_negative(old_dentry))) + return -ENOENT; + if (exchange) { + if (unlikely(d_is_negative(new_dentry))) + return -ENOENT; + access_request_parent1 = + get_mode_access(d_backing_inode(new_dentry)->i_mode); + } else { + access_request_parent1 = 0; + } + access_request_parent2 = + get_mode_access(d_backing_inode(old_dentry)->i_mode); + if (removable) { + access_request_parent1 |= maybe_remove(old_dentry); + access_request_parent2 |= maybe_remove(new_dentry); + } + + /* The mount points are the same for old and new paths, cf. EXDEV. */ + if (old_dentry->d_parent == new_dir->dentry) { + /* + * The LANDLOCK_ACCESS_FS_REFER access right is not required + * for same-directory referer (i.e. no reparenting). + */ + access_request_parent1 = init_layer_masks( + dom, access_request_parent1 | access_request_parent2, + &layer_masks_parent1); + return check_access_path_dual(dom, new_dir, + access_request_parent1, + &layer_masks_parent1, NULL, 0, + NULL, NULL); + } + + access_request_parent1 |= LANDLOCK_ACCESS_FS_REFER; + access_request_parent2 |= LANDLOCK_ACCESS_FS_REFER; + + /* Saves the common mount point. */ + mnt_dir.mnt = new_dir->mnt; + mnt_dir.dentry = new_dir->mnt->mnt_root; + + /* new_dir->dentry is equal to new_dentry->d_parent */ + allow_parent1 = collect_domain_accesses(dom, mnt_dir.dentry, + old_dentry->d_parent, + &layer_masks_parent1); + allow_parent2 = collect_domain_accesses( + dom, mnt_dir.dentry, new_dir->dentry, &layer_masks_parent2); + + if (allow_parent1 && allow_parent2) + return 0; + + /* + * To be able to compare source and destination domain access rights, + * take into account the @old_dentry access rights aggregated with its + * parent access rights. This will be useful to compare with the + * destination parent access rights. + */ + return check_access_path_dual(dom, &mnt_dir, access_request_parent1, + &layer_masks_parent1, old_dentry, + access_request_parent2, + &layer_masks_parent2, + exchange ? new_dentry : NULL); +} + +/* Inode hooks */ + +static void hook_inode_free_security(struct inode *const inode) +{ + /* + * All inodes must already have been untied from their object by + * release_inode() or hook_sb_delete(). + */ + WARN_ON_ONCE(landlock_inode(inode)->object); +} + +/* Super-block hooks */ + +/* + * Release the inodes used in a security policy. + * + * Cf. fsnotify_unmount_inodes() and invalidate_inodes() + */ +static void hook_sb_delete(struct super_block *const sb) +{ + struct inode *inode, *prev_inode = NULL; + + if (!landlock_initialized) + return; + + spin_lock(&sb->s_inode_list_lock); + list_for_each_entry(inode, &sb->s_inodes, i_sb_list) { + struct landlock_object *object; + + /* Only handles referenced inodes. */ + if (!atomic_read(&inode->i_count)) + continue; + + /* + * Protects against concurrent modification of inode (e.g. + * from get_inode_object()). + */ + spin_lock(&inode->i_lock); + /* + * Checks I_FREEING and I_WILL_FREE to protect against a race + * condition when release_inode() just called iput(), which + * could lead to a NULL dereference of inode->security or a + * second call to iput() for the same Landlock object. Also + * checks I_NEW because such inode cannot be tied to an object. + */ + if (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW)) { + spin_unlock(&inode->i_lock); + continue; + } + + rcu_read_lock(); + object = rcu_dereference(landlock_inode(inode)->object); + if (!object) { + rcu_read_unlock(); + spin_unlock(&inode->i_lock); + continue; + } + /* Keeps a reference to this inode until the next loop walk. */ + __iget(inode); + spin_unlock(&inode->i_lock); + + /* + * If there is no concurrent release_inode() ongoing, then we + * are in charge of calling iput() on this inode, otherwise we + * will just wait for it to finish. + */ + spin_lock(&object->lock); + if (object->underobj == inode) { + object->underobj = NULL; + spin_unlock(&object->lock); + rcu_read_unlock(); + + /* + * Because object->underobj was not NULL, + * release_inode() and get_inode_object() guarantee + * that it is safe to reset + * landlock_inode(inode)->object while it is not NULL. + * It is therefore not necessary to lock inode->i_lock. + */ + rcu_assign_pointer(landlock_inode(inode)->object, NULL); + /* + * At this point, we own the ihold() reference that was + * originally set up by get_inode_object() and the + * __iget() reference that we just set in this loop + * walk. Therefore the following call to iput() will + * not sleep nor drop the inode because there is now at + * least two references to it. + */ + iput(inode); + } else { + spin_unlock(&object->lock); + rcu_read_unlock(); + } + + if (prev_inode) { + /* + * At this point, we still own the __iget() reference + * that we just set in this loop walk. Therefore we + * can drop the list lock and know that the inode won't + * disappear from under us until the next loop walk. + */ + spin_unlock(&sb->s_inode_list_lock); + /* + * We can now actually put the inode reference from the + * previous loop walk, which is not needed anymore. + */ + iput(prev_inode); + cond_resched(); + spin_lock(&sb->s_inode_list_lock); + } + prev_inode = inode; + } + spin_unlock(&sb->s_inode_list_lock); + + /* Puts the inode reference from the last loop walk, if any. */ + if (prev_inode) + iput(prev_inode); + /* Waits for pending iput() in release_inode(). */ + wait_var_event(&landlock_superblock(sb)->inode_refs, + !atomic_long_read(&landlock_superblock(sb)->inode_refs)); +} + +/* + * Because a Landlock security policy is defined according to the filesystem + * topology (i.e. the mount namespace), changing it may grant access to files + * not previously allowed. + * + * To make it simple, deny any filesystem topology modification by landlocked + * processes. Non-landlocked processes may still change the namespace of a + * landlocked process, but this kind of threat must be handled by a system-wide + * access-control security policy. + * + * This could be lifted in the future if Landlock can safely handle mount + * namespace updates requested by a landlocked process. Indeed, we could + * update the current domain (which is currently read-only) by taking into + * account the accesses of the source and the destination of a new mount point. + * However, it would also require to make all the child domains dynamically + * inherit these new constraints. Anyway, for backward compatibility reasons, + * a dedicated user space option would be required (e.g. as a ruleset flag). + */ +static int hook_sb_mount(const char *const dev_name, + const struct path *const path, const char *const type, + const unsigned long flags, void *const data) +{ + if (!landlock_get_current_domain()) + return 0; + return -EPERM; +} + +static int hook_move_mount(const struct path *const from_path, + const struct path *const to_path) +{ + if (!landlock_get_current_domain()) + return 0; + return -EPERM; +} + +/* + * Removing a mount point may reveal a previously hidden file hierarchy, which + * may then grant access to files, which may have previously been forbidden. + */ +static int hook_sb_umount(struct vfsmount *const mnt, const int flags) +{ + if (!landlock_get_current_domain()) + return 0; + return -EPERM; +} + +static int hook_sb_remount(struct super_block *const sb, void *const mnt_opts) +{ + if (!landlock_get_current_domain()) + return 0; + return -EPERM; +} + +/* + * pivot_root(2), like mount(2), changes the current mount namespace. It must + * then be forbidden for a landlocked process. + * + * However, chroot(2) may be allowed because it only changes the relative root + * directory of the current process. Moreover, it can be used to restrict the + * view of the filesystem. + */ +static int hook_sb_pivotroot(const struct path *const old_path, + const struct path *const new_path) +{ + if (!landlock_get_current_domain()) + return 0; + return -EPERM; +} + +/* Path hooks */ + +static int hook_path_link(struct dentry *const old_dentry, + const struct path *const new_dir, + struct dentry *const new_dentry) +{ + return current_check_refer_path(old_dentry, new_dir, new_dentry, false, + false); +} + +static int hook_path_rename(const struct path *const old_dir, + struct dentry *const old_dentry, + const struct path *const new_dir, + struct dentry *const new_dentry, + const unsigned int flags) +{ + /* old_dir refers to old_dentry->d_parent and new_dir->mnt */ + return current_check_refer_path(old_dentry, new_dir, new_dentry, true, + !!(flags & RENAME_EXCHANGE)); +} + +static int hook_path_mkdir(const struct path *const dir, + struct dentry *const dentry, const umode_t mode) +{ + return current_check_access_path(dir, LANDLOCK_ACCESS_FS_MAKE_DIR); +} + +static int hook_path_mknod(const struct path *const dir, + struct dentry *const dentry, const umode_t mode, + const unsigned int dev) +{ + const struct landlock_ruleset *const dom = + landlock_get_current_domain(); + + if (!dom) + return 0; + return check_access_path(dom, dir, get_mode_access(mode)); +} + +static int hook_path_symlink(const struct path *const dir, + struct dentry *const dentry, + const char *const old_name) +{ + return current_check_access_path(dir, LANDLOCK_ACCESS_FS_MAKE_SYM); +} + +static int hook_path_unlink(const struct path *const dir, + struct dentry *const dentry) +{ + return current_check_access_path(dir, LANDLOCK_ACCESS_FS_REMOVE_FILE); +} + +static int hook_path_rmdir(const struct path *const dir, + struct dentry *const dentry) +{ + return current_check_access_path(dir, LANDLOCK_ACCESS_FS_REMOVE_DIR); +} + +/* File hooks */ + +static inline access_mask_t get_file_access(const struct file *const file) +{ + access_mask_t access = 0; + + if (file->f_mode & FMODE_READ) { + /* A directory can only be opened in read mode. */ + if (S_ISDIR(file_inode(file)->i_mode)) + return LANDLOCK_ACCESS_FS_READ_DIR; + access = LANDLOCK_ACCESS_FS_READ_FILE; + } + if (file->f_mode & FMODE_WRITE) + access |= LANDLOCK_ACCESS_FS_WRITE_FILE; + /* __FMODE_EXEC is indeed part of f_flags, not f_mode. */ + if (file->f_flags & __FMODE_EXEC) + access |= LANDLOCK_ACCESS_FS_EXECUTE; + return access; +} + +static int hook_file_open(struct file *const file) +{ + const struct landlock_ruleset *const dom = + landlock_get_current_domain(); + + if (!dom) + return 0; + /* + * Because a file may be opened with O_PATH, get_file_access() may + * return 0. This case will be handled with a future Landlock + * evolution. + */ + return check_access_path(dom, &file->f_path, get_file_access(file)); +} + +static struct security_hook_list landlock_hooks[] __lsm_ro_after_init = { + LSM_HOOK_INIT(inode_free_security, hook_inode_free_security), + + LSM_HOOK_INIT(sb_delete, hook_sb_delete), + LSM_HOOK_INIT(sb_mount, hook_sb_mount), + LSM_HOOK_INIT(move_mount, hook_move_mount), + LSM_HOOK_INIT(sb_umount, hook_sb_umount), + LSM_HOOK_INIT(sb_remount, hook_sb_remount), + LSM_HOOK_INIT(sb_pivotroot, hook_sb_pivotroot), + + LSM_HOOK_INIT(path_link, hook_path_link), + LSM_HOOK_INIT(path_rename, hook_path_rename), + LSM_HOOK_INIT(path_mkdir, hook_path_mkdir), + LSM_HOOK_INIT(path_mknod, hook_path_mknod), + LSM_HOOK_INIT(path_symlink, hook_path_symlink), + LSM_HOOK_INIT(path_unlink, hook_path_unlink), + LSM_HOOK_INIT(path_rmdir, hook_path_rmdir), + + LSM_HOOK_INIT(file_open, hook_file_open), +}; + +__init void landlock_add_fs_hooks(void) +{ + security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks), + LANDLOCK_NAME); +} diff --git a/security/landlock/fs.h b/security/landlock/fs.h new file mode 100644 index 000000000..8db7acf91 --- /dev/null +++ b/security/landlock/fs.h @@ -0,0 +1,71 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Landlock LSM - Filesystem management and hooks + * + * Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net> + * Copyright © 2018-2020 ANSSI + */ + +#ifndef _SECURITY_LANDLOCK_FS_H +#define _SECURITY_LANDLOCK_FS_H + +#include <linux/fs.h> +#include <linux/init.h> +#include <linux/rcupdate.h> + +#include "ruleset.h" +#include "setup.h" + +/** + * struct landlock_inode_security - Inode security blob + * + * Enable to reference a &struct landlock_object tied to an inode (i.e. + * underlying object). + */ +struct landlock_inode_security { + /** + * @object: Weak pointer to an allocated object. All assignments of a + * new object are protected by the underlying inode->i_lock. However, + * atomically disassociating @object from the inode is only protected + * by @object->lock, from the time @object's usage refcount drops to + * zero to the time this pointer is nulled out (cf. release_inode() and + * hook_sb_delete()). Indeed, such disassociation doesn't require + * inode->i_lock thanks to the careful rcu_access_pointer() check + * performed by get_inode_object(). + */ + struct landlock_object __rcu *object; +}; + +/** + * struct landlock_superblock_security - Superblock security blob + * + * Enable hook_sb_delete() to wait for concurrent calls to release_inode(). + */ +struct landlock_superblock_security { + /** + * @inode_refs: Number of pending inodes (from this superblock) that + * are being released by release_inode(). + * Cf. struct super_block->s_fsnotify_inode_refs . + */ + atomic_long_t inode_refs; +}; + +static inline struct landlock_inode_security * +landlock_inode(const struct inode *const inode) +{ + return inode->i_security + landlock_blob_sizes.lbs_inode; +} + +static inline struct landlock_superblock_security * +landlock_superblock(const struct super_block *const superblock) +{ + return superblock->s_security + landlock_blob_sizes.lbs_superblock; +} + +__init void landlock_add_fs_hooks(void); + +int landlock_append_fs_rule(struct landlock_ruleset *const ruleset, + const struct path *const path, + access_mask_t access_hierarchy); + +#endif /* _SECURITY_LANDLOCK_FS_H */ diff --git a/security/landlock/limits.h b/security/landlock/limits.h new file mode 100644 index 000000000..b54184ab9 --- /dev/null +++ b/security/landlock/limits.h @@ -0,0 +1,27 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Landlock LSM - Limits for different components + * + * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net> + * Copyright © 2018-2020 ANSSI + */ + +#ifndef _SECURITY_LANDLOCK_LIMITS_H +#define _SECURITY_LANDLOCK_LIMITS_H + +#include <linux/bitops.h> +#include <linux/limits.h> +#include <uapi/linux/landlock.h> + +/* clang-format off */ + +#define LANDLOCK_MAX_NUM_LAYERS 16 +#define LANDLOCK_MAX_NUM_RULES U32_MAX + +#define LANDLOCK_LAST_ACCESS_FS LANDLOCK_ACCESS_FS_REFER +#define LANDLOCK_MASK_ACCESS_FS ((LANDLOCK_LAST_ACCESS_FS << 1) - 1) +#define LANDLOCK_NUM_ACCESS_FS __const_hweight64(LANDLOCK_MASK_ACCESS_FS) + +/* clang-format on */ + +#endif /* _SECURITY_LANDLOCK_LIMITS_H */ diff --git a/security/landlock/object.c b/security/landlock/object.c new file mode 100644 index 000000000..1f50612f0 --- /dev/null +++ b/security/landlock/object.c @@ -0,0 +1,67 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Landlock LSM - Object management + * + * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net> + * Copyright © 2018-2020 ANSSI + */ + +#include <linux/bug.h> +#include <linux/compiler_types.h> +#include <linux/err.h> +#include <linux/kernel.h> +#include <linux/rcupdate.h> +#include <linux/refcount.h> +#include <linux/slab.h> +#include <linux/spinlock.h> + +#include "object.h" + +struct landlock_object * +landlock_create_object(const struct landlock_object_underops *const underops, + void *const underobj) +{ + struct landlock_object *new_object; + + if (WARN_ON_ONCE(!underops || !underobj)) + return ERR_PTR(-ENOENT); + new_object = kzalloc(sizeof(*new_object), GFP_KERNEL_ACCOUNT); + if (!new_object) + return ERR_PTR(-ENOMEM); + refcount_set(&new_object->usage, 1); + spin_lock_init(&new_object->lock); + new_object->underops = underops; + new_object->underobj = underobj; + return new_object; +} + +/* + * The caller must own the object (i.e. thanks to object->usage) to safely put + * it. + */ +void landlock_put_object(struct landlock_object *const object) +{ + /* + * The call to @object->underops->release(object) might sleep, e.g. + * because of iput(). + */ + might_sleep(); + if (!object) + return; + + /* + * If the @object's refcount cannot drop to zero, we can just decrement + * the refcount without holding a lock. Otherwise, the decrement must + * happen under @object->lock for synchronization with things like + * get_inode_object(). + */ + if (refcount_dec_and_lock(&object->usage, &object->lock)) { + __acquire(&object->lock); + /* + * With @object->lock initially held, remove the reference from + * @object->underobj to @object (if it still exists). + */ + object->underops->release(object); + kfree_rcu(object, rcu_free); + } +} diff --git a/security/landlock/object.h b/security/landlock/object.h new file mode 100644 index 000000000..5f28c35e8 --- /dev/null +++ b/security/landlock/object.h @@ -0,0 +1,91 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Landlock LSM - Object management + * + * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net> + * Copyright © 2018-2020 ANSSI + */ + +#ifndef _SECURITY_LANDLOCK_OBJECT_H +#define _SECURITY_LANDLOCK_OBJECT_H + +#include <linux/compiler_types.h> +#include <linux/refcount.h> +#include <linux/spinlock.h> + +struct landlock_object; + +/** + * struct landlock_object_underops - Operations on an underlying object + */ +struct landlock_object_underops { + /** + * @release: Releases the underlying object (e.g. iput() for an inode). + */ + void (*release)(struct landlock_object *const object) + __releases(object->lock); +}; + +/** + * struct landlock_object - Security blob tied to a kernel object + * + * The goal of this structure is to enable to tie a set of ephemeral access + * rights (pertaining to different domains) to a kernel object (e.g an inode) + * in a safe way. This implies to handle concurrent use and modification. + * + * The lifetime of a &struct landlock_object depends on the rules referring to + * it. + */ +struct landlock_object { + /** + * @usage: This counter is used to tie an object to the rules matching + * it or to keep it alive while adding a new rule. If this counter + * reaches zero, this struct must not be modified, but this counter can + * still be read from within an RCU read-side critical section. When + * adding a new rule to an object with a usage counter of zero, we must + * wait until the pointer to this object is set to NULL (or recycled). + */ + refcount_t usage; + /** + * @lock: Protects against concurrent modifications. This lock must be + * held from the time @usage drops to zero until any weak references + * from @underobj to this object have been cleaned up. + * + * Lock ordering: inode->i_lock nests inside this. + */ + spinlock_t lock; + /** + * @underobj: Used when cleaning up an object and to mark an object as + * tied to its underlying kernel structure. This pointer is protected + * by @lock. Cf. landlock_release_inodes() and release_inode(). + */ + void *underobj; + union { + /** + * @rcu_free: Enables lockless use of @usage, @lock and + * @underobj from within an RCU read-side critical section. + * @rcu_free and @underops are only used by + * landlock_put_object(). + */ + struct rcu_head rcu_free; + /** + * @underops: Enables landlock_put_object() to release the + * underlying object (e.g. inode). + */ + const struct landlock_object_underops *underops; + }; +}; + +struct landlock_object * +landlock_create_object(const struct landlock_object_underops *const underops, + void *const underobj); + +void landlock_put_object(struct landlock_object *const object); + +static inline void landlock_get_object(struct landlock_object *const object) +{ + if (object) + refcount_inc(&object->usage); +} + +#endif /* _SECURITY_LANDLOCK_OBJECT_H */ diff --git a/security/landlock/ptrace.c b/security/landlock/ptrace.c new file mode 100644 index 000000000..4c5b9cd71 --- /dev/null +++ b/security/landlock/ptrace.c @@ -0,0 +1,120 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Landlock LSM - Ptrace hooks + * + * Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net> + * Copyright © 2019-2020 ANSSI + */ + +#include <asm/current.h> +#include <linux/cred.h> +#include <linux/errno.h> +#include <linux/kernel.h> +#include <linux/lsm_hooks.h> +#include <linux/rcupdate.h> +#include <linux/sched.h> + +#include "common.h" +#include "cred.h" +#include "ptrace.h" +#include "ruleset.h" +#include "setup.h" + +/** + * domain_scope_le - Checks domain ordering for scoped ptrace + * + * @parent: Parent domain. + * @child: Potential child of @parent. + * + * Checks if the @parent domain is less or equal to (i.e. an ancestor, which + * means a subset of) the @child domain. + */ +static bool domain_scope_le(const struct landlock_ruleset *const parent, + const struct landlock_ruleset *const child) +{ + const struct landlock_hierarchy *walker; + + if (!parent) + return true; + if (!child) + return false; + for (walker = child->hierarchy; walker; walker = walker->parent) { + if (walker == parent->hierarchy) + /* @parent is in the scoped hierarchy of @child. */ + return true; + } + /* There is no relationship between @parent and @child. */ + return false; +} + +static bool task_is_scoped(const struct task_struct *const parent, + const struct task_struct *const child) +{ + bool is_scoped; + const struct landlock_ruleset *dom_parent, *dom_child; + + rcu_read_lock(); + dom_parent = landlock_get_task_domain(parent); + dom_child = landlock_get_task_domain(child); + is_scoped = domain_scope_le(dom_parent, dom_child); + rcu_read_unlock(); + return is_scoped; +} + +static int task_ptrace(const struct task_struct *const parent, + const struct task_struct *const child) +{ + /* Quick return for non-landlocked tasks. */ + if (!landlocked(parent)) + return 0; + if (task_is_scoped(parent, child)) + return 0; + return -EPERM; +} + +/** + * hook_ptrace_access_check - Determines whether the current process may access + * another + * + * @child: Process to be accessed. + * @mode: Mode of attachment. + * + * If the current task has Landlock rules, then the child must have at least + * the same rules. Else denied. + * + * Determines whether a process may access another, returning 0 if permission + * granted, -errno if denied. + */ +static int hook_ptrace_access_check(struct task_struct *const child, + const unsigned int mode) +{ + return task_ptrace(current, child); +} + +/** + * hook_ptrace_traceme - Determines whether another process may trace the + * current one + * + * @parent: Task proposed to be the tracer. + * + * If the parent has Landlock rules, then the current task must have the same + * or more rules. Else denied. + * + * Determines whether the nominated task is permitted to trace the current + * process, returning 0 if permission is granted, -errno if denied. + */ +static int hook_ptrace_traceme(struct task_struct *const parent) +{ + return task_ptrace(parent, current); +} + +static struct security_hook_list landlock_hooks[] __lsm_ro_after_init = { + LSM_HOOK_INIT(ptrace_access_check, hook_ptrace_access_check), + LSM_HOOK_INIT(ptrace_traceme, hook_ptrace_traceme), +}; + +__init void landlock_add_ptrace_hooks(void) +{ + security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks), + LANDLOCK_NAME); +} diff --git a/security/landlock/ptrace.h b/security/landlock/ptrace.h new file mode 100644 index 000000000..265b220ae --- /dev/null +++ b/security/landlock/ptrace.h @@ -0,0 +1,14 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Landlock LSM - Ptrace hooks + * + * Copyright © 2017-2019 Mickaël Salaün <mic@digikod.net> + * Copyright © 2019 ANSSI + */ + +#ifndef _SECURITY_LANDLOCK_PTRACE_H +#define _SECURITY_LANDLOCK_PTRACE_H + +__init void landlock_add_ptrace_hooks(void); + +#endif /* _SECURITY_LANDLOCK_PTRACE_H */ diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c new file mode 100644 index 000000000..996484f98 --- /dev/null +++ b/security/landlock/ruleset.c @@ -0,0 +1,475 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Landlock LSM - Ruleset management + * + * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net> + * Copyright © 2018-2020 ANSSI + */ + +#include <linux/bits.h> +#include <linux/bug.h> +#include <linux/compiler_types.h> +#include <linux/err.h> +#include <linux/errno.h> +#include <linux/kernel.h> +#include <linux/lockdep.h> +#include <linux/overflow.h> +#include <linux/rbtree.h> +#include <linux/refcount.h> +#include <linux/slab.h> +#include <linux/spinlock.h> +#include <linux/workqueue.h> + +#include "limits.h" +#include "object.h" +#include "ruleset.h" + +static struct landlock_ruleset *create_ruleset(const u32 num_layers) +{ + struct landlock_ruleset *new_ruleset; + + new_ruleset = + kzalloc(struct_size(new_ruleset, fs_access_masks, num_layers), + GFP_KERNEL_ACCOUNT); + if (!new_ruleset) + return ERR_PTR(-ENOMEM); + refcount_set(&new_ruleset->usage, 1); + mutex_init(&new_ruleset->lock); + new_ruleset->root = RB_ROOT; + new_ruleset->num_layers = num_layers; + /* + * hierarchy = NULL + * num_rules = 0 + * fs_access_masks[] = 0 + */ + return new_ruleset; +} + +struct landlock_ruleset * +landlock_create_ruleset(const access_mask_t fs_access_mask) +{ + struct landlock_ruleset *new_ruleset; + + /* Informs about useless ruleset. */ + if (!fs_access_mask) + return ERR_PTR(-ENOMSG); + new_ruleset = create_ruleset(1); + if (!IS_ERR(new_ruleset)) + new_ruleset->fs_access_masks[0] = fs_access_mask; + return new_ruleset; +} + +static void build_check_rule(void) +{ + const struct landlock_rule rule = { + .num_layers = ~0, + }; + + BUILD_BUG_ON(rule.num_layers < LANDLOCK_MAX_NUM_LAYERS); +} + +static struct landlock_rule * +create_rule(struct landlock_object *const object, + const struct landlock_layer (*const layers)[], const u32 num_layers, + const struct landlock_layer *const new_layer) +{ + struct landlock_rule *new_rule; + u32 new_num_layers; + + build_check_rule(); + if (new_layer) { + /* Should already be checked by landlock_merge_ruleset(). */ + if (WARN_ON_ONCE(num_layers >= LANDLOCK_MAX_NUM_LAYERS)) + return ERR_PTR(-E2BIG); + new_num_layers = num_layers + 1; + } else { + new_num_layers = num_layers; + } + new_rule = kzalloc(struct_size(new_rule, layers, new_num_layers), + GFP_KERNEL_ACCOUNT); + if (!new_rule) + return ERR_PTR(-ENOMEM); + RB_CLEAR_NODE(&new_rule->node); + landlock_get_object(object); + new_rule->object = object; + new_rule->num_layers = new_num_layers; + /* Copies the original layer stack. */ + memcpy(new_rule->layers, layers, + flex_array_size(new_rule, layers, num_layers)); + if (new_layer) + /* Adds a copy of @new_layer on the layer stack. */ + new_rule->layers[new_rule->num_layers - 1] = *new_layer; + return new_rule; +} + +static void free_rule(struct landlock_rule *const rule) +{ + might_sleep(); + if (!rule) + return; + landlock_put_object(rule->object); + kfree(rule); +} + +static void build_check_ruleset(void) +{ + const struct landlock_ruleset ruleset = { + .num_rules = ~0, + .num_layers = ~0, + }; + typeof(ruleset.fs_access_masks[0]) fs_access_mask = ~0; + + BUILD_BUG_ON(ruleset.num_rules < LANDLOCK_MAX_NUM_RULES); + BUILD_BUG_ON(ruleset.num_layers < LANDLOCK_MAX_NUM_LAYERS); + BUILD_BUG_ON(fs_access_mask < LANDLOCK_MASK_ACCESS_FS); +} + +/** + * insert_rule - Create and insert a rule in a ruleset + * + * @ruleset: The ruleset to be updated. + * @object: The object to build the new rule with. The underlying kernel + * object must be held by the caller. + * @layers: One or multiple layers to be copied into the new rule. + * @num_layers: The number of @layers entries. + * + * When user space requests to add a new rule to a ruleset, @layers only + * contains one entry and this entry is not assigned to any level. In this + * case, the new rule will extend @ruleset, similarly to a boolean OR between + * access rights. + * + * When merging a ruleset in a domain, or copying a domain, @layers will be + * added to @ruleset as new constraints, similarly to a boolean AND between + * access rights. + */ +static int insert_rule(struct landlock_ruleset *const ruleset, + struct landlock_object *const object, + const struct landlock_layer (*const layers)[], + size_t num_layers) +{ + struct rb_node **walker_node; + struct rb_node *parent_node = NULL; + struct landlock_rule *new_rule; + + might_sleep(); + lockdep_assert_held(&ruleset->lock); + if (WARN_ON_ONCE(!object || !layers)) + return -ENOENT; + walker_node = &(ruleset->root.rb_node); + while (*walker_node) { + struct landlock_rule *const this = + rb_entry(*walker_node, struct landlock_rule, node); + + if (this->object != object) { + parent_node = *walker_node; + if (this->object < object) + walker_node = &((*walker_node)->rb_right); + else + walker_node = &((*walker_node)->rb_left); + continue; + } + + /* Only a single-level layer should match an existing rule. */ + if (WARN_ON_ONCE(num_layers != 1)) + return -EINVAL; + + /* If there is a matching rule, updates it. */ + if ((*layers)[0].level == 0) { + /* + * Extends access rights when the request comes from + * landlock_add_rule(2), i.e. @ruleset is not a domain. + */ + if (WARN_ON_ONCE(this->num_layers != 1)) + return -EINVAL; + if (WARN_ON_ONCE(this->layers[0].level != 0)) + return -EINVAL; + this->layers[0].access |= (*layers)[0].access; + return 0; + } + + if (WARN_ON_ONCE(this->layers[0].level == 0)) + return -EINVAL; + + /* + * Intersects access rights when it is a merge between a + * ruleset and a domain. + */ + new_rule = create_rule(object, &this->layers, this->num_layers, + &(*layers)[0]); + if (IS_ERR(new_rule)) + return PTR_ERR(new_rule); + rb_replace_node(&this->node, &new_rule->node, &ruleset->root); + free_rule(this); + return 0; + } + + /* There is no match for @object. */ + build_check_ruleset(); + if (ruleset->num_rules >= LANDLOCK_MAX_NUM_RULES) + return -E2BIG; + new_rule = create_rule(object, layers, num_layers, NULL); + if (IS_ERR(new_rule)) + return PTR_ERR(new_rule); + rb_link_node(&new_rule->node, parent_node, walker_node); + rb_insert_color(&new_rule->node, &ruleset->root); + ruleset->num_rules++; + return 0; +} + +static void build_check_layer(void) +{ + const struct landlock_layer layer = { + .level = ~0, + .access = ~0, + }; + + BUILD_BUG_ON(layer.level < LANDLOCK_MAX_NUM_LAYERS); + BUILD_BUG_ON(layer.access < LANDLOCK_MASK_ACCESS_FS); +} + +/* @ruleset must be locked by the caller. */ +int landlock_insert_rule(struct landlock_ruleset *const ruleset, + struct landlock_object *const object, + const access_mask_t access) +{ + struct landlock_layer layers[] = { { + .access = access, + /* When @level is zero, insert_rule() extends @ruleset. */ + .level = 0, + } }; + + build_check_layer(); + return insert_rule(ruleset, object, &layers, ARRAY_SIZE(layers)); +} + +static inline void get_hierarchy(struct landlock_hierarchy *const hierarchy) +{ + if (hierarchy) + refcount_inc(&hierarchy->usage); +} + +static void put_hierarchy(struct landlock_hierarchy *hierarchy) +{ + while (hierarchy && refcount_dec_and_test(&hierarchy->usage)) { + const struct landlock_hierarchy *const freeme = hierarchy; + + hierarchy = hierarchy->parent; + kfree(freeme); + } +} + +static int merge_ruleset(struct landlock_ruleset *const dst, + struct landlock_ruleset *const src) +{ + struct landlock_rule *walker_rule, *next_rule; + int err = 0; + + might_sleep(); + /* Should already be checked by landlock_merge_ruleset() */ + if (WARN_ON_ONCE(!src)) + return 0; + /* Only merge into a domain. */ + if (WARN_ON_ONCE(!dst || !dst->hierarchy)) + return -EINVAL; + + /* Locks @dst first because we are its only owner. */ + mutex_lock(&dst->lock); + mutex_lock_nested(&src->lock, SINGLE_DEPTH_NESTING); + + /* Stacks the new layer. */ + if (WARN_ON_ONCE(src->num_layers != 1 || dst->num_layers < 1)) { + err = -EINVAL; + goto out_unlock; + } + dst->fs_access_masks[dst->num_layers - 1] = src->fs_access_masks[0]; + + /* Merges the @src tree. */ + rbtree_postorder_for_each_entry_safe(walker_rule, next_rule, &src->root, + node) { + struct landlock_layer layers[] = { { + .level = dst->num_layers, + } }; + + if (WARN_ON_ONCE(walker_rule->num_layers != 1)) { + err = -EINVAL; + goto out_unlock; + } + if (WARN_ON_ONCE(walker_rule->layers[0].level != 0)) { + err = -EINVAL; + goto out_unlock; + } + layers[0].access = walker_rule->layers[0].access; + err = insert_rule(dst, walker_rule->object, &layers, + ARRAY_SIZE(layers)); + if (err) + goto out_unlock; + } + +out_unlock: + mutex_unlock(&src->lock); + mutex_unlock(&dst->lock); + return err; +} + +static int inherit_ruleset(struct landlock_ruleset *const parent, + struct landlock_ruleset *const child) +{ + struct landlock_rule *walker_rule, *next_rule; + int err = 0; + + might_sleep(); + if (!parent) + return 0; + + /* Locks @child first because we are its only owner. */ + mutex_lock(&child->lock); + mutex_lock_nested(&parent->lock, SINGLE_DEPTH_NESTING); + + /* Copies the @parent tree. */ + rbtree_postorder_for_each_entry_safe(walker_rule, next_rule, + &parent->root, node) { + err = insert_rule(child, walker_rule->object, + &walker_rule->layers, + walker_rule->num_layers); + if (err) + goto out_unlock; + } + + if (WARN_ON_ONCE(child->num_layers <= parent->num_layers)) { + err = -EINVAL; + goto out_unlock; + } + /* Copies the parent layer stack and leaves a space for the new layer. */ + memcpy(child->fs_access_masks, parent->fs_access_masks, + flex_array_size(parent, fs_access_masks, parent->num_layers)); + + if (WARN_ON_ONCE(!parent->hierarchy)) { + err = -EINVAL; + goto out_unlock; + } + get_hierarchy(parent->hierarchy); + child->hierarchy->parent = parent->hierarchy; + +out_unlock: + mutex_unlock(&parent->lock); + mutex_unlock(&child->lock); + return err; +} + +static void free_ruleset(struct landlock_ruleset *const ruleset) +{ + struct landlock_rule *freeme, *next; + + might_sleep(); + rbtree_postorder_for_each_entry_safe(freeme, next, &ruleset->root, node) + free_rule(freeme); + put_hierarchy(ruleset->hierarchy); + kfree(ruleset); +} + +void landlock_put_ruleset(struct landlock_ruleset *const ruleset) +{ + might_sleep(); + if (ruleset && refcount_dec_and_test(&ruleset->usage)) + free_ruleset(ruleset); +} + +static void free_ruleset_work(struct work_struct *const work) +{ + struct landlock_ruleset *ruleset; + + ruleset = container_of(work, struct landlock_ruleset, work_free); + free_ruleset(ruleset); +} + +void landlock_put_ruleset_deferred(struct landlock_ruleset *const ruleset) +{ + if (ruleset && refcount_dec_and_test(&ruleset->usage)) { + INIT_WORK(&ruleset->work_free, free_ruleset_work); + schedule_work(&ruleset->work_free); + } +} + +/** + * landlock_merge_ruleset - Merge a ruleset with a domain + * + * @parent: Parent domain. + * @ruleset: New ruleset to be merged. + * + * Returns the intersection of @parent and @ruleset, or returns @parent if + * @ruleset is empty, or returns a duplicate of @ruleset if @parent is empty. + */ +struct landlock_ruleset * +landlock_merge_ruleset(struct landlock_ruleset *const parent, + struct landlock_ruleset *const ruleset) +{ + struct landlock_ruleset *new_dom; + u32 num_layers; + int err; + + might_sleep(); + if (WARN_ON_ONCE(!ruleset || parent == ruleset)) + return ERR_PTR(-EINVAL); + + if (parent) { + if (parent->num_layers >= LANDLOCK_MAX_NUM_LAYERS) + return ERR_PTR(-E2BIG); + num_layers = parent->num_layers + 1; + } else { + num_layers = 1; + } + + /* Creates a new domain... */ + new_dom = create_ruleset(num_layers); + if (IS_ERR(new_dom)) + return new_dom; + new_dom->hierarchy = + kzalloc(sizeof(*new_dom->hierarchy), GFP_KERNEL_ACCOUNT); + if (!new_dom->hierarchy) { + err = -ENOMEM; + goto out_put_dom; + } + refcount_set(&new_dom->hierarchy->usage, 1); + + /* ...as a child of @parent... */ + err = inherit_ruleset(parent, new_dom); + if (err) + goto out_put_dom; + + /* ...and including @ruleset. */ + err = merge_ruleset(new_dom, ruleset); + if (err) + goto out_put_dom; + + return new_dom; + +out_put_dom: + landlock_put_ruleset(new_dom); + return ERR_PTR(err); +} + +/* + * The returned access has the same lifetime as @ruleset. + */ +const struct landlock_rule * +landlock_find_rule(const struct landlock_ruleset *const ruleset, + const struct landlock_object *const object) +{ + const struct rb_node *node; + + if (!object) + return NULL; + node = ruleset->root.rb_node; + while (node) { + struct landlock_rule *this = + rb_entry(node, struct landlock_rule, node); + + if (this->object == object) + return this; + if (this->object < object) + node = node->rb_right; + else + node = node->rb_left; + } + return NULL; +} diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h new file mode 100644 index 000000000..d43231b78 --- /dev/null +++ b/security/landlock/ruleset.h @@ -0,0 +1,180 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Landlock LSM - Ruleset management + * + * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net> + * Copyright © 2018-2020 ANSSI + */ + +#ifndef _SECURITY_LANDLOCK_RULESET_H +#define _SECURITY_LANDLOCK_RULESET_H + +#include <linux/bitops.h> +#include <linux/build_bug.h> +#include <linux/mutex.h> +#include <linux/rbtree.h> +#include <linux/refcount.h> +#include <linux/workqueue.h> + +#include "limits.h" +#include "object.h" + +typedef u16 access_mask_t; +/* Makes sure all filesystem access rights can be stored. */ +static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_ACCESS_FS); +/* Makes sure for_each_set_bit() and for_each_clear_bit() calls are OK. */ +static_assert(sizeof(unsigned long) >= sizeof(access_mask_t)); + +typedef u16 layer_mask_t; +/* Makes sure all layers can be checked. */ +static_assert(BITS_PER_TYPE(layer_mask_t) >= LANDLOCK_MAX_NUM_LAYERS); + +/** + * struct landlock_layer - Access rights for a given layer + */ +struct landlock_layer { + /** + * @level: Position of this layer in the layer stack. + */ + u16 level; + /** + * @access: Bitfield of allowed actions on the kernel object. They are + * relative to the object type (e.g. %LANDLOCK_ACTION_FS_READ). + */ + access_mask_t access; +}; + +/** + * struct landlock_rule - Access rights tied to an object + */ +struct landlock_rule { + /** + * @node: Node in the ruleset's red-black tree. + */ + struct rb_node node; + /** + * @object: Pointer to identify a kernel object (e.g. an inode). This + * is used as a key for this ruleset element. This pointer is set once + * and never modified. It always points to an allocated object because + * each rule increments the refcount of its object. + */ + struct landlock_object *object; + /** + * @num_layers: Number of entries in @layers. + */ + u32 num_layers; + /** + * @layers: Stack of layers, from the latest to the newest, implemented + * as a flexible array member (FAM). + */ + struct landlock_layer layers[]; +}; + +/** + * struct landlock_hierarchy - Node in a ruleset hierarchy + */ +struct landlock_hierarchy { + /** + * @parent: Pointer to the parent node, or NULL if it is a root + * Landlock domain. + */ + struct landlock_hierarchy *parent; + /** + * @usage: Number of potential children domains plus their parent + * domain. + */ + refcount_t usage; +}; + +/** + * struct landlock_ruleset - Landlock ruleset + * + * This data structure must contain unique entries, be updatable, and quick to + * match an object. + */ +struct landlock_ruleset { + /** + * @root: Root of a red-black tree containing &struct landlock_rule + * nodes. Once a ruleset is tied to a process (i.e. as a domain), this + * tree is immutable until @usage reaches zero. + */ + struct rb_root root; + /** + * @hierarchy: Enables hierarchy identification even when a parent + * domain vanishes. This is needed for the ptrace protection. + */ + struct landlock_hierarchy *hierarchy; + union { + /** + * @work_free: Enables to free a ruleset within a lockless + * section. This is only used by + * landlock_put_ruleset_deferred() when @usage reaches zero. + * The fields @lock, @usage, @num_rules, @num_layers and + * @fs_access_masks are then unused. + */ + struct work_struct work_free; + struct { + /** + * @lock: Protects against concurrent modifications of + * @root, if @usage is greater than zero. + */ + struct mutex lock; + /** + * @usage: Number of processes (i.e. domains) or file + * descriptors referencing this ruleset. + */ + refcount_t usage; + /** + * @num_rules: Number of non-overlapping (i.e. not for + * the same object) rules in this ruleset. + */ + u32 num_rules; + /** + * @num_layers: Number of layers that are used in this + * ruleset. This enables to check that all the layers + * allow an access request. A value of 0 identifies a + * non-merged ruleset (i.e. not a domain). + */ + u32 num_layers; + /** + * @fs_access_masks: Contains the subset of filesystem + * actions that are restricted by a ruleset. A domain + * saves all layers of merged rulesets in a stack + * (FAM), starting from the first layer to the last + * one. These layers are used when merging rulesets, + * for user space backward compatibility (i.e. + * future-proof), and to properly handle merged + * rulesets without overlapping access rights. These + * layers are set once and never changed for the + * lifetime of the ruleset. + */ + access_mask_t fs_access_masks[]; + }; + }; +}; + +struct landlock_ruleset * +landlock_create_ruleset(const access_mask_t fs_access_mask); + +void landlock_put_ruleset(struct landlock_ruleset *const ruleset); +void landlock_put_ruleset_deferred(struct landlock_ruleset *const ruleset); + +int landlock_insert_rule(struct landlock_ruleset *const ruleset, + struct landlock_object *const object, + const access_mask_t access); + +struct landlock_ruleset * +landlock_merge_ruleset(struct landlock_ruleset *const parent, + struct landlock_ruleset *const ruleset); + +const struct landlock_rule * +landlock_find_rule(const struct landlock_ruleset *const ruleset, + const struct landlock_object *const object); + +static inline void landlock_get_ruleset(struct landlock_ruleset *const ruleset) +{ + if (ruleset) + refcount_inc(&ruleset->usage); +} + +#endif /* _SECURITY_LANDLOCK_RULESET_H */ diff --git a/security/landlock/setup.c b/security/landlock/setup.c new file mode 100644 index 000000000..f8e8e9804 --- /dev/null +++ b/security/landlock/setup.c @@ -0,0 +1,40 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Landlock LSM - Security framework setup + * + * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net> + * Copyright © 2018-2020 ANSSI + */ + +#include <linux/init.h> +#include <linux/lsm_hooks.h> + +#include "common.h" +#include "cred.h" +#include "fs.h" +#include "ptrace.h" +#include "setup.h" + +bool landlock_initialized __lsm_ro_after_init = false; + +struct lsm_blob_sizes landlock_blob_sizes __lsm_ro_after_init = { + .lbs_cred = sizeof(struct landlock_cred_security), + .lbs_inode = sizeof(struct landlock_inode_security), + .lbs_superblock = sizeof(struct landlock_superblock_security), +}; + +static int __init landlock_init(void) +{ + landlock_add_cred_hooks(); + landlock_add_ptrace_hooks(); + landlock_add_fs_hooks(); + landlock_initialized = true; + pr_info("Up and running.\n"); + return 0; +} + +DEFINE_LSM(LANDLOCK_NAME) = { + .name = LANDLOCK_NAME, + .init = landlock_init, + .blobs = &landlock_blob_sizes, +}; diff --git a/security/landlock/setup.h b/security/landlock/setup.h new file mode 100644 index 000000000..1daffab1a --- /dev/null +++ b/security/landlock/setup.h @@ -0,0 +1,18 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Landlock LSM - Security framework setup + * + * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net> + * Copyright © 2018-2020 ANSSI + */ + +#ifndef _SECURITY_LANDLOCK_SETUP_H +#define _SECURITY_LANDLOCK_SETUP_H + +#include <linux/lsm_hooks.h> + +extern bool landlock_initialized; + +extern struct lsm_blob_sizes landlock_blob_sizes; + +#endif /* _SECURITY_LANDLOCK_SETUP_H */ diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c new file mode 100644 index 000000000..2ca0ccbd9 --- /dev/null +++ b/security/landlock/syscalls.c @@ -0,0 +1,456 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Landlock LSM - System call implementations and user space interfaces + * + * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net> + * Copyright © 2018-2020 ANSSI + */ + +#include <asm/current.h> +#include <linux/anon_inodes.h> +#include <linux/build_bug.h> +#include <linux/capability.h> +#include <linux/compiler_types.h> +#include <linux/dcache.h> +#include <linux/err.h> +#include <linux/errno.h> +#include <linux/fs.h> +#include <linux/limits.h> +#include <linux/mount.h> +#include <linux/path.h> +#include <linux/sched.h> +#include <linux/security.h> +#include <linux/stddef.h> +#include <linux/syscalls.h> +#include <linux/types.h> +#include <linux/uaccess.h> +#include <uapi/linux/landlock.h> + +#include "cred.h" +#include "fs.h" +#include "limits.h" +#include "ruleset.h" +#include "setup.h" + +/** + * copy_min_struct_from_user - Safe future-proof argument copying + * + * Extend copy_struct_from_user() to check for consistent user buffer. + * + * @dst: Kernel space pointer or NULL. + * @ksize: Actual size of the data pointed to by @dst. + * @ksize_min: Minimal required size to be copied. + * @src: User space pointer or NULL. + * @usize: (Alleged) size of the data pointed to by @src. + */ +static __always_inline int +copy_min_struct_from_user(void *const dst, const size_t ksize, + const size_t ksize_min, const void __user *const src, + const size_t usize) +{ + /* Checks buffer inconsistencies. */ + BUILD_BUG_ON(!dst); + if (!src) + return -EFAULT; + + /* Checks size ranges. */ + BUILD_BUG_ON(ksize <= 0); + BUILD_BUG_ON(ksize < ksize_min); + if (usize < ksize_min) + return -EINVAL; + if (usize > PAGE_SIZE) + return -E2BIG; + + /* Copies user buffer and fills with zeros. */ + return copy_struct_from_user(dst, ksize, src, usize); +} + +/* + * This function only contains arithmetic operations with constants, leading to + * BUILD_BUG_ON(). The related code is evaluated and checked at build time, + * but it is then ignored thanks to compiler optimizations. + */ +static void build_check_abi(void) +{ + struct landlock_ruleset_attr ruleset_attr; + struct landlock_path_beneath_attr path_beneath_attr; + size_t ruleset_size, path_beneath_size; + + /* + * For each user space ABI structures, first checks that there is no + * hole in them, then checks that all architectures have the same + * struct size. + */ + ruleset_size = sizeof(ruleset_attr.handled_access_fs); + BUILD_BUG_ON(sizeof(ruleset_attr) != ruleset_size); + BUILD_BUG_ON(sizeof(ruleset_attr) != 8); + + path_beneath_size = sizeof(path_beneath_attr.allowed_access); + path_beneath_size += sizeof(path_beneath_attr.parent_fd); + BUILD_BUG_ON(sizeof(path_beneath_attr) != path_beneath_size); + BUILD_BUG_ON(sizeof(path_beneath_attr) != 12); +} + +/* Ruleset handling */ + +static int fop_ruleset_release(struct inode *const inode, + struct file *const filp) +{ + struct landlock_ruleset *ruleset = filp->private_data; + + landlock_put_ruleset(ruleset); + return 0; +} + +static ssize_t fop_dummy_read(struct file *const filp, char __user *const buf, + const size_t size, loff_t *const ppos) +{ + /* Dummy handler to enable FMODE_CAN_READ. */ + return -EINVAL; +} + +static ssize_t fop_dummy_write(struct file *const filp, + const char __user *const buf, const size_t size, + loff_t *const ppos) +{ + /* Dummy handler to enable FMODE_CAN_WRITE. */ + return -EINVAL; +} + +/* + * A ruleset file descriptor enables to build a ruleset by adding (i.e. + * writing) rule after rule, without relying on the task's context. This + * reentrant design is also used in a read way to enforce the ruleset on the + * current task. + */ +static const struct file_operations ruleset_fops = { + .release = fop_ruleset_release, + .read = fop_dummy_read, + .write = fop_dummy_write, +}; + +#define LANDLOCK_ABI_VERSION 2 + +/** + * sys_landlock_create_ruleset - Create a new ruleset + * + * @attr: Pointer to a &struct landlock_ruleset_attr identifying the scope of + * the new ruleset. + * @size: Size of the pointed &struct landlock_ruleset_attr (needed for + * backward and forward compatibility). + * @flags: Supported value: %LANDLOCK_CREATE_RULESET_VERSION. + * + * This system call enables to create a new Landlock ruleset, and returns the + * related file descriptor on success. + * + * If @flags is %LANDLOCK_CREATE_RULESET_VERSION and @attr is NULL and @size is + * 0, then the returned value is the highest supported Landlock ABI version + * (starting at 1). + * + * Possible returned errors are: + * + * - %EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time; + * - %EINVAL: unknown @flags, or unknown access, or too small @size; + * - %E2BIG or %EFAULT: @attr or @size inconsistencies; + * - %ENOMSG: empty &landlock_ruleset_attr.handled_access_fs. + */ +SYSCALL_DEFINE3(landlock_create_ruleset, + const struct landlock_ruleset_attr __user *const, attr, + const size_t, size, const __u32, flags) +{ + struct landlock_ruleset_attr ruleset_attr; + struct landlock_ruleset *ruleset; + int err, ruleset_fd; + + /* Build-time checks. */ + build_check_abi(); + + if (!landlock_initialized) + return -EOPNOTSUPP; + + if (flags) { + if ((flags == LANDLOCK_CREATE_RULESET_VERSION) && !attr && + !size) + return LANDLOCK_ABI_VERSION; + return -EINVAL; + } + + /* Copies raw user space buffer. */ + err = copy_min_struct_from_user(&ruleset_attr, sizeof(ruleset_attr), + offsetofend(typeof(ruleset_attr), + handled_access_fs), + attr, size); + if (err) + return err; + + /* Checks content (and 32-bits cast). */ + if ((ruleset_attr.handled_access_fs | LANDLOCK_MASK_ACCESS_FS) != + LANDLOCK_MASK_ACCESS_FS) + return -EINVAL; + + /* Checks arguments and transforms to kernel struct. */ + ruleset = landlock_create_ruleset(ruleset_attr.handled_access_fs); + if (IS_ERR(ruleset)) + return PTR_ERR(ruleset); + + /* Creates anonymous FD referring to the ruleset. */ + ruleset_fd = anon_inode_getfd("[landlock-ruleset]", &ruleset_fops, + ruleset, O_RDWR | O_CLOEXEC); + if (ruleset_fd < 0) + landlock_put_ruleset(ruleset); + return ruleset_fd; +} + +/* + * Returns an owned ruleset from a FD. It is thus needed to call + * landlock_put_ruleset() on the return value. + */ +static struct landlock_ruleset *get_ruleset_from_fd(const int fd, + const fmode_t mode) +{ + struct fd ruleset_f; + struct landlock_ruleset *ruleset; + + ruleset_f = fdget(fd); + if (!ruleset_f.file) + return ERR_PTR(-EBADF); + + /* Checks FD type and access right. */ + if (ruleset_f.file->f_op != &ruleset_fops) { + ruleset = ERR_PTR(-EBADFD); + goto out_fdput; + } + if (!(ruleset_f.file->f_mode & mode)) { + ruleset = ERR_PTR(-EPERM); + goto out_fdput; + } + ruleset = ruleset_f.file->private_data; + if (WARN_ON_ONCE(ruleset->num_layers != 1)) { + ruleset = ERR_PTR(-EINVAL); + goto out_fdput; + } + landlock_get_ruleset(ruleset); + +out_fdput: + fdput(ruleset_f); + return ruleset; +} + +/* Path handling */ + +/* + * @path: Must call put_path(@path) after the call if it succeeded. + */ +static int get_path_from_fd(const s32 fd, struct path *const path) +{ + struct fd f; + int err = 0; + + BUILD_BUG_ON(!__same_type( + fd, ((struct landlock_path_beneath_attr *)NULL)->parent_fd)); + + /* Handles O_PATH. */ + f = fdget_raw(fd); + if (!f.file) + return -EBADF; + /* + * Forbids ruleset FDs, internal filesystems (e.g. nsfs), including + * pseudo filesystems that will never be mountable (e.g. sockfs, + * pipefs). + */ + if ((f.file->f_op == &ruleset_fops) || + (f.file->f_path.mnt->mnt_flags & MNT_INTERNAL) || + (f.file->f_path.dentry->d_sb->s_flags & SB_NOUSER) || + d_is_negative(f.file->f_path.dentry) || + IS_PRIVATE(d_backing_inode(f.file->f_path.dentry))) { + err = -EBADFD; + goto out_fdput; + } + *path = f.file->f_path; + path_get(path); + +out_fdput: + fdput(f); + return err; +} + +/** + * sys_landlock_add_rule - Add a new rule to a ruleset + * + * @ruleset_fd: File descriptor tied to the ruleset that should be extended + * with the new rule. + * @rule_type: Identify the structure type pointed to by @rule_attr (only + * %LANDLOCK_RULE_PATH_BENEATH for now). + * @rule_attr: Pointer to a rule (only of type &struct + * landlock_path_beneath_attr for now). + * @flags: Must be 0. + * + * This system call enables to define a new rule and add it to an existing + * ruleset. + * + * Possible returned errors are: + * + * - %EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time; + * - %EINVAL: @flags is not 0, or inconsistent access in the rule (i.e. + * &landlock_path_beneath_attr.allowed_access is not a subset of the + * ruleset handled accesses); + * - %ENOMSG: Empty accesses (e.g. &landlock_path_beneath_attr.allowed_access); + * - %EBADF: @ruleset_fd is not a file descriptor for the current thread, or a + * member of @rule_attr is not a file descriptor as expected; + * - %EBADFD: @ruleset_fd is not a ruleset file descriptor, or a member of + * @rule_attr is not the expected file descriptor type; + * - %EPERM: @ruleset_fd has no write access to the underlying ruleset; + * - %EFAULT: @rule_attr inconsistency. + */ +SYSCALL_DEFINE4(landlock_add_rule, const int, ruleset_fd, + const enum landlock_rule_type, rule_type, + const void __user *const, rule_attr, const __u32, flags) +{ + struct landlock_path_beneath_attr path_beneath_attr; + struct path path; + struct landlock_ruleset *ruleset; + int res, err; + + if (!landlock_initialized) + return -EOPNOTSUPP; + + /* No flag for now. */ + if (flags) + return -EINVAL; + + /* Gets and checks the ruleset. */ + ruleset = get_ruleset_from_fd(ruleset_fd, FMODE_CAN_WRITE); + if (IS_ERR(ruleset)) + return PTR_ERR(ruleset); + + if (rule_type != LANDLOCK_RULE_PATH_BENEATH) { + err = -EINVAL; + goto out_put_ruleset; + } + + /* Copies raw user space buffer, only one type for now. */ + res = copy_from_user(&path_beneath_attr, rule_attr, + sizeof(path_beneath_attr)); + if (res) { + err = -EFAULT; + goto out_put_ruleset; + } + + /* + * Informs about useless rule: empty allowed_access (i.e. deny rules) + * are ignored in path walks. + */ + if (!path_beneath_attr.allowed_access) { + err = -ENOMSG; + goto out_put_ruleset; + } + /* + * Checks that allowed_access matches the @ruleset constraints + * (ruleset->fs_access_masks[0] is automatically upgraded to 64-bits). + */ + if ((path_beneath_attr.allowed_access | ruleset->fs_access_masks[0]) != + ruleset->fs_access_masks[0]) { + err = -EINVAL; + goto out_put_ruleset; + } + + /* Gets and checks the new rule. */ + err = get_path_from_fd(path_beneath_attr.parent_fd, &path); + if (err) + goto out_put_ruleset; + + /* Imports the new rule. */ + err = landlock_append_fs_rule(ruleset, &path, + path_beneath_attr.allowed_access); + path_put(&path); + +out_put_ruleset: + landlock_put_ruleset(ruleset); + return err; +} + +/* Enforcement */ + +/** + * sys_landlock_restrict_self - Enforce a ruleset on the calling thread + * + * @ruleset_fd: File descriptor tied to the ruleset to merge with the target. + * @flags: Must be 0. + * + * This system call enables to enforce a Landlock ruleset on the current + * thread. Enforcing a ruleset requires that the task has %CAP_SYS_ADMIN in its + * namespace or is running with no_new_privs. This avoids scenarios where + * unprivileged tasks can affect the behavior of privileged children. + * + * Possible returned errors are: + * + * - %EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time; + * - %EINVAL: @flags is not 0. + * - %EBADF: @ruleset_fd is not a file descriptor for the current thread; + * - %EBADFD: @ruleset_fd is not a ruleset file descriptor; + * - %EPERM: @ruleset_fd has no read access to the underlying ruleset, or the + * current thread is not running with no_new_privs, or it doesn't have + * %CAP_SYS_ADMIN in its namespace. + * - %E2BIG: The maximum number of stacked rulesets is reached for the current + * thread. + */ +SYSCALL_DEFINE2(landlock_restrict_self, const int, ruleset_fd, const __u32, + flags) +{ + struct landlock_ruleset *new_dom, *ruleset; + struct cred *new_cred; + struct landlock_cred_security *new_llcred; + int err; + + if (!landlock_initialized) + return -EOPNOTSUPP; + + /* + * Similar checks as for seccomp(2), except that an -EPERM may be + * returned. + */ + if (!task_no_new_privs(current) && + !ns_capable_noaudit(current_user_ns(), CAP_SYS_ADMIN)) + return -EPERM; + + /* No flag for now. */ + if (flags) + return -EINVAL; + + /* Gets and checks the ruleset. */ + ruleset = get_ruleset_from_fd(ruleset_fd, FMODE_CAN_READ); + if (IS_ERR(ruleset)) + return PTR_ERR(ruleset); + + /* Prepares new credentials. */ + new_cred = prepare_creds(); + if (!new_cred) { + err = -ENOMEM; + goto out_put_ruleset; + } + new_llcred = landlock_cred(new_cred); + + /* + * There is no possible race condition while copying and manipulating + * the current credentials because they are dedicated per thread. + */ + new_dom = landlock_merge_ruleset(new_llcred->domain, ruleset); + if (IS_ERR(new_dom)) { + err = PTR_ERR(new_dom); + goto out_put_creds; + } + + /* Replaces the old (prepared) domain. */ + landlock_put_ruleset(new_llcred->domain); + new_llcred->domain = new_dom; + + landlock_put_ruleset(ruleset); + return commit_creds(new_cred); + +out_put_creds: + abort_creds(new_cred); + +out_put_ruleset: + landlock_put_ruleset(ruleset); + return err; +} |