diff options
Diffstat (limited to 'fs/verity/signature.c')
| -rw-r--r-- | fs/verity/signature.c | 176 |
1 files changed, 176 insertions, 0 deletions
diff --git a/fs/verity/signature.c b/fs/verity/signature.c new file mode 100644 index 000000000..ed32afc23 --- /dev/null +++ b/fs/verity/signature.c @@ -0,0 +1,176 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * fs/verity/signature.c: verification of builtin signatures + * + * Copyright 2019 Google LLC + */ + +#include "fsverity_private.h" + +#include <linux/cred.h> +#include <linux/key.h> +#include <linux/slab.h> +#include <linux/verification.h> + +/* + * /proc/sys/fs/verity/require_signatures + * If 1, all verity files must have a valid builtin signature. + */ +static int fsverity_require_signatures; + +/* + * Keyring that contains the trusted X.509 certificates. + * + * Only root (kuid=0) can modify this. Also, root may use + * keyctl_restrict_keyring() to prevent any more additions. + */ +static struct key *fsverity_keyring; + +/** + * fsverity_verify_signature() - check a verity file's signature + * @vi: the file's fsverity_info + * @desc: the file's fsverity_descriptor + * @desc_size: size of @desc + * + * If the file's fs-verity descriptor includes a signature of the file + * measurement, verify it against the certificates in the fs-verity keyring. + * + * Return: 0 on success (signature valid or not required); -errno on failure + */ +int fsverity_verify_signature(const struct fsverity_info *vi, + const struct fsverity_descriptor *desc, + size_t desc_size) +{ + const struct inode *inode = vi->inode; + const struct fsverity_hash_alg *hash_alg = vi->tree_params.hash_alg; + const u32 sig_size = le32_to_cpu(desc->sig_size); + struct fsverity_signed_digest *d; + int err; + + if (sig_size == 0) { + if (fsverity_require_signatures) { + fsverity_err(inode, + "require_signatures=1, rejecting unsigned file!"); + return -EPERM; + } + return 0; + } + + if (sig_size > desc_size - sizeof(*desc)) { + fsverity_err(inode, "Signature overflows verity descriptor"); + return -EBADMSG; + } + + if (fsverity_keyring->keys.nr_leaves_on_tree == 0) { + /* + * The ".fs-verity" keyring is empty, due to builtin signatures + * being supported by the kernel but not actually being used. + * In this case, verify_pkcs7_signature() would always return an + * error, usually ENOKEY. It could also be EBADMSG if the + * PKCS#7 is malformed, but that isn't very important to + * distinguish. So, just skip to ENOKEY to avoid the attack + * surface of the PKCS#7 parser, which would otherwise be + * reachable by any task able to execute FS_IOC_ENABLE_VERITY. + */ + fsverity_err(inode, + "fs-verity keyring is empty, rejecting signed file!"); + return -ENOKEY; + } + + d = kzalloc(sizeof(*d) + hash_alg->digest_size, GFP_KERNEL); + if (!d) + return -ENOMEM; + memcpy(d->magic, "FSVerity", 8); + d->digest_algorithm = cpu_to_le16(hash_alg - fsverity_hash_algs); + d->digest_size = cpu_to_le16(hash_alg->digest_size); + memcpy(d->digest, vi->measurement, hash_alg->digest_size); + + err = verify_pkcs7_signature(d, sizeof(*d) + hash_alg->digest_size, + desc->signature, sig_size, + fsverity_keyring, + VERIFYING_UNSPECIFIED_SIGNATURE, + NULL, NULL); + kfree(d); + + if (err) { + if (err == -ENOKEY) + fsverity_err(inode, + "File's signing cert isn't in the fs-verity keyring"); + else if (err == -EKEYREJECTED) + fsverity_err(inode, "Incorrect file signature"); + else if (err == -EBADMSG) + fsverity_err(inode, "Malformed file signature"); + else + fsverity_err(inode, "Error %d verifying file signature", + err); + return err; + } + + pr_debug("Valid signature for file measurement %s:%*phN\n", + hash_alg->name, hash_alg->digest_size, vi->measurement); + return 0; +} + +#ifdef CONFIG_SYSCTL +static struct ctl_table_header *fsverity_sysctl_header; + +static const struct ctl_path fsverity_sysctl_path[] = { + { .procname = "fs", }, + { .procname = "verity", }, + { } +}; + +static struct ctl_table fsverity_sysctl_table[] = { + { + .procname = "require_signatures", + .data = &fsverity_require_signatures, + .maxlen = sizeof(int), + .mode = 0644, + .proc_handler = proc_dointvec_minmax, + .extra1 = SYSCTL_ZERO, + .extra2 = SYSCTL_ONE, + }, + { } +}; + +static int __init fsverity_sysctl_init(void) +{ + fsverity_sysctl_header = register_sysctl_paths(fsverity_sysctl_path, + fsverity_sysctl_table); + if (!fsverity_sysctl_header) { + pr_err("sysctl registration failed!\n"); + return -ENOMEM; + } + return 0; +} +#else /* !CONFIG_SYSCTL */ +static inline int __init fsverity_sysctl_init(void) +{ + return 0; +} +#endif /* !CONFIG_SYSCTL */ + +int __init fsverity_init_signature(void) +{ + struct key *ring; + int err; + + ring = keyring_alloc(".fs-verity", KUIDT_INIT(0), KGIDT_INIT(0), + current_cred(), KEY_POS_SEARCH | + KEY_USR_VIEW | KEY_USR_READ | KEY_USR_WRITE | + KEY_USR_SEARCH | KEY_USR_SETATTR, + KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL); + if (IS_ERR(ring)) + return PTR_ERR(ring); + + err = fsverity_sysctl_init(); + if (err) + goto err_put_ring; + + fsverity_keyring = ring; + return 0; + +err_put_ring: + key_put(ring); + return err; +} |