diff options
Diffstat (limited to 'security/yama')
| -rw-r--r-- | security/yama/Kconfig | 14 | ||||
| -rw-r--r-- | security/yama/Makefile | 4 | ||||
| -rw-r--r-- | security/yama/yama_lsm.c | 488 |
3 files changed, 506 insertions, 0 deletions
diff --git a/security/yama/Kconfig b/security/yama/Kconfig new file mode 100644 index 000000000..a81030412 --- /dev/null +++ b/security/yama/Kconfig @@ -0,0 +1,14 @@ +# SPDX-License-Identifier: GPL-2.0-only +config SECURITY_YAMA + bool "Yama support" + depends on SECURITY + default n + help + This selects Yama, which extends DAC support with additional + system-wide security settings beyond regular Linux discretionary + access controls. Currently available is ptrace scope restriction. + Like capabilities, this security module stacks with other LSMs. + Further information can be found in + Documentation/admin-guide/LSM/Yama.rst. + + If you are unsure how to answer this question, answer N. diff --git a/security/yama/Makefile b/security/yama/Makefile new file mode 100644 index 000000000..0fa5d0fe2 --- /dev/null +++ b/security/yama/Makefile @@ -0,0 +1,4 @@ +# SPDX-License-Identifier: GPL-2.0-only +obj-$(CONFIG_SECURITY_YAMA) := yama.o + +yama-y := yama_lsm.o diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c new file mode 100644 index 000000000..06e226166 --- /dev/null +++ b/security/yama/yama_lsm.c @@ -0,0 +1,488 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Yama Linux Security Module + * + * Author: Kees Cook <keescook@chromium.org> + * + * Copyright (C) 2010 Canonical, Ltd. + * Copyright (C) 2011 The Chromium OS Authors. + */ + +#include <linux/lsm_hooks.h> +#include <linux/sysctl.h> +#include <linux/ptrace.h> +#include <linux/prctl.h> +#include <linux/ratelimit.h> +#include <linux/workqueue.h> +#include <linux/string_helpers.h> +#include <linux/task_work.h> +#include <linux/sched.h> +#include <linux/spinlock.h> + +#define YAMA_SCOPE_DISABLED 0 +#define YAMA_SCOPE_RELATIONAL 1 +#define YAMA_SCOPE_CAPABILITY 2 +#define YAMA_SCOPE_NO_ATTACH 3 + +static int ptrace_scope = YAMA_SCOPE_RELATIONAL; + +/* describe a ptrace relationship for potential exception */ +struct ptrace_relation { + struct task_struct *tracer; + struct task_struct *tracee; + bool invalid; + struct list_head node; + struct rcu_head rcu; +}; + +static LIST_HEAD(ptracer_relations); +static DEFINE_SPINLOCK(ptracer_relations_lock); + +static void yama_relation_cleanup(struct work_struct *work); +static DECLARE_WORK(yama_relation_work, yama_relation_cleanup); + +struct access_report_info { + struct callback_head work; + const char *access; + struct task_struct *target; + struct task_struct *agent; +}; + +static void __report_access(struct callback_head *work) +{ + struct access_report_info *info = + container_of(work, struct access_report_info, work); + char *target_cmd, *agent_cmd; + + target_cmd = kstrdup_quotable_cmdline(info->target, GFP_KERNEL); + agent_cmd = kstrdup_quotable_cmdline(info->agent, GFP_KERNEL); + + pr_notice_ratelimited( + "ptrace %s of \"%s\"[%d] was attempted by \"%s\"[%d]\n", + info->access, target_cmd, info->target->pid, agent_cmd, + info->agent->pid); + + kfree(agent_cmd); + kfree(target_cmd); + + put_task_struct(info->agent); + put_task_struct(info->target); + kfree(info); +} + +/* defers execution because cmdline access can sleep */ +static void report_access(const char *access, struct task_struct *target, + struct task_struct *agent) +{ + struct access_report_info *info; + char agent_comm[sizeof(agent->comm)]; + + assert_spin_locked(&target->alloc_lock); /* for target->comm */ + + if (current->flags & PF_KTHREAD) { + /* I don't think kthreads call task_work_run() before exiting. + * Imagine angry ranting about procfs here. + */ + pr_notice_ratelimited( + "ptrace %s of \"%s\"[%d] was attempted by \"%s\"[%d]\n", + access, target->comm, target->pid, + get_task_comm(agent_comm, agent), agent->pid); + return; + } + + info = kmalloc(sizeof(*info), GFP_ATOMIC); + if (!info) + return; + init_task_work(&info->work, __report_access); + get_task_struct(target); + get_task_struct(agent); + info->access = access; + info->target = target; + info->agent = agent; + if (task_work_add(current, &info->work, TWA_RESUME) == 0) + return; /* success */ + + WARN(1, "report_access called from exiting task"); + put_task_struct(target); + put_task_struct(agent); + kfree(info); +} + +/** + * yama_relation_cleanup - remove invalid entries from the relation list + * + */ +static void yama_relation_cleanup(struct work_struct *work) +{ + struct ptrace_relation *relation; + + spin_lock(&ptracer_relations_lock); + rcu_read_lock(); + list_for_each_entry_rcu(relation, &ptracer_relations, node) { + if (relation->invalid) { + list_del_rcu(&relation->node); + kfree_rcu(relation, rcu); + } + } + rcu_read_unlock(); + spin_unlock(&ptracer_relations_lock); +} + +/** + * yama_ptracer_add - add/replace an exception for this tracer/tracee pair + * @tracer: the task_struct of the process doing the ptrace + * @tracee: the task_struct of the process to be ptraced + * + * Each tracee can have, at most, one tracer registered. Each time this + * is called, the prior registered tracer will be replaced for the tracee. + * + * Returns 0 if relationship was added, -ve on error. + */ +static int yama_ptracer_add(struct task_struct *tracer, + struct task_struct *tracee) +{ + struct ptrace_relation *relation, *added; + + added = kmalloc(sizeof(*added), GFP_KERNEL); + if (!added) + return -ENOMEM; + + added->tracee = tracee; + added->tracer = tracer; + added->invalid = false; + + spin_lock(&ptracer_relations_lock); + rcu_read_lock(); + list_for_each_entry_rcu(relation, &ptracer_relations, node) { + if (relation->invalid) + continue; + if (relation->tracee == tracee) { + list_replace_rcu(&relation->node, &added->node); + kfree_rcu(relation, rcu); + goto out; + } + } + + list_add_rcu(&added->node, &ptracer_relations); + +out: + rcu_read_unlock(); + spin_unlock(&ptracer_relations_lock); + return 0; +} + +/** + * yama_ptracer_del - remove exceptions related to the given tasks + * @tracer: remove any relation where tracer task matches + * @tracee: remove any relation where tracee task matches + */ +static void yama_ptracer_del(struct task_struct *tracer, + struct task_struct *tracee) +{ + struct ptrace_relation *relation; + bool marked = false; + + rcu_read_lock(); + list_for_each_entry_rcu(relation, &ptracer_relations, node) { + if (relation->invalid) + continue; + if (relation->tracee == tracee || + (tracer && relation->tracer == tracer)) { + relation->invalid = true; + marked = true; + } + } + rcu_read_unlock(); + + if (marked) + schedule_work(&yama_relation_work); +} + +/** + * yama_task_free - check for task_pid to remove from exception list + * @task: task being removed + */ +static void yama_task_free(struct task_struct *task) +{ + yama_ptracer_del(task, task); +} + +/** + * yama_task_prctl - check for Yama-specific prctl operations + * @option: operation + * @arg2: argument + * @arg3: argument + * @arg4: argument + * @arg5: argument + * + * Return 0 on success, -ve on error. -ENOSYS is returned when Yama + * does not handle the given option. + */ +static int yama_task_prctl(int option, unsigned long arg2, unsigned long arg3, + unsigned long arg4, unsigned long arg5) +{ + int rc = -ENOSYS; + struct task_struct *myself = current; + + switch (option) { + case PR_SET_PTRACER: + /* Since a thread can call prctl(), find the group leader + * before calling _add() or _del() on it, since we want + * process-level granularity of control. The tracer group + * leader checking is handled later when walking the ancestry + * at the time of PTRACE_ATTACH check. + */ + rcu_read_lock(); + if (!thread_group_leader(myself)) + myself = rcu_dereference(myself->group_leader); + get_task_struct(myself); + rcu_read_unlock(); + + if (arg2 == 0) { + yama_ptracer_del(NULL, myself); + rc = 0; + } else if (arg2 == PR_SET_PTRACER_ANY || (int)arg2 == -1) { + rc = yama_ptracer_add(NULL, myself); + } else { + struct task_struct *tracer; + + tracer = find_get_task_by_vpid(arg2); + if (!tracer) { + rc = -EINVAL; + } else { + rc = yama_ptracer_add(tracer, myself); + put_task_struct(tracer); + } + } + + put_task_struct(myself); + break; + } + + return rc; +} + +/** + * task_is_descendant - walk up a process family tree looking for a match + * @parent: the process to compare against while walking up from child + * @child: the process to start from while looking upwards for parent + * + * Returns 1 if child is a descendant of parent, 0 if not. + */ +static int task_is_descendant(struct task_struct *parent, + struct task_struct *child) +{ + int rc = 0; + struct task_struct *walker = child; + + if (!parent || !child) + return 0; + + rcu_read_lock(); + if (!thread_group_leader(parent)) + parent = rcu_dereference(parent->group_leader); + while (walker->pid > 0) { + if (!thread_group_leader(walker)) + walker = rcu_dereference(walker->group_leader); + if (walker == parent) { + rc = 1; + break; + } + walker = rcu_dereference(walker->real_parent); + } + rcu_read_unlock(); + + return rc; +} + +/** + * ptracer_exception_found - tracer registered as exception for this tracee + * @tracer: the task_struct of the process attempting ptrace + * @tracee: the task_struct of the process to be ptraced + * + * Returns 1 if tracer has a ptracer exception ancestor for tracee. + */ +static int ptracer_exception_found(struct task_struct *tracer, + struct task_struct *tracee) +{ + int rc = 0; + struct ptrace_relation *relation; + struct task_struct *parent = NULL; + bool found = false; + + rcu_read_lock(); + + /* + * If there's already an active tracing relationship, then make an + * exception for the sake of other accesses, like process_vm_rw(). + */ + parent = ptrace_parent(tracee); + if (parent != NULL && same_thread_group(parent, tracer)) { + rc = 1; + goto unlock; + } + + /* Look for a PR_SET_PTRACER relationship. */ + if (!thread_group_leader(tracee)) + tracee = rcu_dereference(tracee->group_leader); + list_for_each_entry_rcu(relation, &ptracer_relations, node) { + if (relation->invalid) + continue; + if (relation->tracee == tracee) { + parent = relation->tracer; + found = true; + break; + } + } + + if (found && (parent == NULL || task_is_descendant(parent, tracer))) + rc = 1; + +unlock: + rcu_read_unlock(); + + return rc; +} + +/** + * yama_ptrace_access_check - validate PTRACE_ATTACH calls + * @child: task that current task is attempting to ptrace + * @mode: ptrace attach mode + * + * Returns 0 if following the ptrace is allowed, -ve on error. + */ +static int yama_ptrace_access_check(struct task_struct *child, + unsigned int mode) +{ + int rc = 0; + + /* require ptrace target be a child of ptracer on attach */ + if (mode & PTRACE_MODE_ATTACH) { + switch (ptrace_scope) { + case YAMA_SCOPE_DISABLED: + /* No additional restrictions. */ + break; + case YAMA_SCOPE_RELATIONAL: + rcu_read_lock(); + if (!pid_alive(child)) + rc = -EPERM; + if (!rc && !task_is_descendant(current, child) && + !ptracer_exception_found(current, child) && + !ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE)) + rc = -EPERM; + rcu_read_unlock(); + break; + case YAMA_SCOPE_CAPABILITY: + rcu_read_lock(); + if (!ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE)) + rc = -EPERM; + rcu_read_unlock(); + break; + case YAMA_SCOPE_NO_ATTACH: + default: + rc = -EPERM; + break; + } + } + + if (rc && (mode & PTRACE_MODE_NOAUDIT) == 0) + report_access("attach", child, current); + + return rc; +} + +/** + * yama_ptrace_traceme - validate PTRACE_TRACEME calls + * @parent: task that will become the ptracer of the current task + * + * Returns 0 if following the ptrace is allowed, -ve on error. + */ +static int yama_ptrace_traceme(struct task_struct *parent) +{ + int rc = 0; + + /* Only disallow PTRACE_TRACEME on more aggressive settings. */ + switch (ptrace_scope) { + case YAMA_SCOPE_CAPABILITY: + if (!has_ns_capability(parent, current_user_ns(), CAP_SYS_PTRACE)) + rc = -EPERM; + break; + case YAMA_SCOPE_NO_ATTACH: + rc = -EPERM; + break; + } + + if (rc) { + task_lock(current); + report_access("traceme", current, parent); + task_unlock(current); + } + + return rc; +} + +static struct security_hook_list yama_hooks[] __lsm_ro_after_init = { + LSM_HOOK_INIT(ptrace_access_check, yama_ptrace_access_check), + LSM_HOOK_INIT(ptrace_traceme, yama_ptrace_traceme), + LSM_HOOK_INIT(task_prctl, yama_task_prctl), + LSM_HOOK_INIT(task_free, yama_task_free), +}; + +#ifdef CONFIG_SYSCTL +static int yama_dointvec_minmax(struct ctl_table *table, int write, + void *buffer, size_t *lenp, loff_t *ppos) +{ + struct ctl_table table_copy; + + if (write && !capable(CAP_SYS_PTRACE)) + return -EPERM; + + /* Lock the max value if it ever gets set. */ + table_copy = *table; + if (*(int *)table_copy.data == *(int *)table_copy.extra2) + table_copy.extra1 = table_copy.extra2; + + return proc_dointvec_minmax(&table_copy, write, buffer, lenp, ppos); +} + +static int max_scope = YAMA_SCOPE_NO_ATTACH; + +static struct ctl_path yama_sysctl_path[] = { + { .procname = "kernel", }, + { .procname = "yama", }, + { } +}; + +static struct ctl_table yama_sysctl_table[] = { + { + .procname = "ptrace_scope", + .data = &ptrace_scope, + .maxlen = sizeof(int), + .mode = 0644, + .proc_handler = yama_dointvec_minmax, + .extra1 = SYSCTL_ZERO, + .extra2 = &max_scope, + }, + { } +}; +static void __init yama_init_sysctl(void) +{ + if (!register_sysctl_paths(yama_sysctl_path, yama_sysctl_table)) + panic("Yama: sysctl registration failed.\n"); +} +#else +static inline void yama_init_sysctl(void) { } +#endif /* CONFIG_SYSCTL */ + +static int __init yama_init(void) +{ + pr_info("Yama: becoming mindful.\n"); + security_add_hooks(yama_hooks, ARRAY_SIZE(yama_hooks), "yama"); + yama_init_sysctl(); + return 0; +} + +DEFINE_LSM(yama) = { + .name = "yama", + .init = yama_init, +}; |