// SPDX-License-Identifier: GPL-2.0 /* * 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 * @signature: the file's built-in signature * @sig_size: size of signature in bytes, or 0 if no signature * * If the file includes a signature of its fs-verity file digest, 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 u8 *signature, size_t sig_size) { const struct inode *inode = vi->inode; const struct fsverity_hash_alg *hash_alg = vi->tree_params.hash_alg; struct fsverity_formatted_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; } 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->file_digest, hash_alg->digest_size); err = verify_pkcs7_signature(d, sizeof(*d) + hash_alg->digest_size, 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 digest %s:%*phN\n", hash_alg->name, hash_alg->digest_size, vi->file_digest); 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; }