1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Verification of builtin signatures 4 * 5 * Copyright 2019 Google LLC 6 */ 7 8 #include "fsverity_private.h" 9 10 #include <linux/cred.h> 11 #include <linux/key.h> 12 #include <linux/slab.h> 13 #include <linux/verification.h> 14 15 /* 16 * /proc/sys/fs/verity/require_signatures 17 * If 1, all verity files must have a valid builtin signature. 18 */ 19 static int fsverity_require_signatures; 20 21 /* 22 * Keyring that contains the trusted X.509 certificates. 23 * 24 * Only root (kuid=0) can modify this. Also, root may use 25 * keyctl_restrict_keyring() to prevent any more additions. 26 */ 27 static struct key *fsverity_keyring; 28 29 /** 30 * fsverity_verify_signature() - check a verity file's signature 31 * @vi: the file's fsverity_info 32 * @signature: the file's built-in signature 33 * @sig_size: size of signature in bytes, or 0 if no signature 34 * 35 * If the file includes a signature of its fs-verity file digest, verify it 36 * against the certificates in the fs-verity keyring. 37 * 38 * Return: 0 on success (signature valid or not required); -errno on failure 39 */ 40 int fsverity_verify_signature(const struct fsverity_info *vi, 41 const u8 *signature, size_t sig_size) 42 { 43 const struct inode *inode = vi->inode; 44 const struct fsverity_hash_alg *hash_alg = vi->tree_params.hash_alg; 45 struct fsverity_formatted_digest *d; 46 int err; 47 48 if (sig_size == 0) { 49 if (fsverity_require_signatures) { 50 fsverity_err(inode, 51 "require_signatures=1, rejecting unsigned file!"); 52 return -EPERM; 53 } 54 return 0; 55 } 56 57 d = kzalloc(sizeof(*d) + hash_alg->digest_size, GFP_KERNEL); 58 if (!d) 59 return -ENOMEM; 60 memcpy(d->magic, "FSVerity", 8); 61 d->digest_algorithm = cpu_to_le16(hash_alg - fsverity_hash_algs); 62 d->digest_size = cpu_to_le16(hash_alg->digest_size); 63 memcpy(d->digest, vi->file_digest, hash_alg->digest_size); 64 65 err = verify_pkcs7_signature(d, sizeof(*d) + hash_alg->digest_size, 66 signature, sig_size, fsverity_keyring, 67 VERIFYING_UNSPECIFIED_SIGNATURE, 68 NULL, NULL); 69 kfree(d); 70 71 if (err) { 72 if (err == -ENOKEY) 73 fsverity_err(inode, 74 "File's signing cert isn't in the fs-verity keyring"); 75 else if (err == -EKEYREJECTED) 76 fsverity_err(inode, "Incorrect file signature"); 77 else if (err == -EBADMSG) 78 fsverity_err(inode, "Malformed file signature"); 79 else 80 fsverity_err(inode, "Error %d verifying file signature", 81 err); 82 return err; 83 } 84 85 return 0; 86 } 87 88 #ifdef CONFIG_SYSCTL 89 static struct ctl_table_header *fsverity_sysctl_header; 90 91 static const struct ctl_path fsverity_sysctl_path[] = { 92 { .procname = "fs", }, 93 { .procname = "verity", }, 94 { } 95 }; 96 97 static struct ctl_table fsverity_sysctl_table[] = { 98 { 99 .procname = "require_signatures", 100 .data = &fsverity_require_signatures, 101 .maxlen = sizeof(int), 102 .mode = 0644, 103 .proc_handler = proc_dointvec_minmax, 104 .extra1 = SYSCTL_ZERO, 105 .extra2 = SYSCTL_ONE, 106 }, 107 { } 108 }; 109 110 static int __init fsverity_sysctl_init(void) 111 { 112 fsverity_sysctl_header = register_sysctl_paths(fsverity_sysctl_path, 113 fsverity_sysctl_table); 114 if (!fsverity_sysctl_header) { 115 pr_err("sysctl registration failed!\n"); 116 return -ENOMEM; 117 } 118 return 0; 119 } 120 #else /* !CONFIG_SYSCTL */ 121 static inline int __init fsverity_sysctl_init(void) 122 { 123 return 0; 124 } 125 #endif /* !CONFIG_SYSCTL */ 126 127 int __init fsverity_init_signature(void) 128 { 129 struct key *ring; 130 int err; 131 132 ring = keyring_alloc(".fs-verity", KUIDT_INIT(0), KGIDT_INIT(0), 133 current_cred(), KEY_POS_SEARCH | 134 KEY_USR_VIEW | KEY_USR_READ | KEY_USR_WRITE | 135 KEY_USR_SEARCH | KEY_USR_SETATTR, 136 KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL); 137 if (IS_ERR(ring)) 138 return PTR_ERR(ring); 139 140 err = fsverity_sysctl_init(); 141 if (err) 142 goto err_put_ring; 143 144 fsverity_keyring = ring; 145 return 0; 146 147 err_put_ring: 148 key_put(ring); 149 return err; 150 } 151