1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Verification of builtin signatures 4 * 5 * Copyright 2019 Google LLC 6 */ 7 8 /* 9 * This file implements verification of fs-verity builtin signatures. Please 10 * take great care before using this feature. It is not the only way to do 11 * signatures with fs-verity, and the alternatives (such as userspace signature 12 * verification, and IMA appraisal) can be much better. For details about the 13 * limitations of this feature, see Documentation/filesystems/fsverity.rst. 14 */ 15 16 #include "fsverity_private.h" 17 18 #include <linux/cred.h> 19 #include <linux/key.h> 20 #include <linux/slab.h> 21 #include <linux/verification.h> 22 23 /* 24 * /proc/sys/fs/verity/require_signatures 25 * If 1, all verity files must have a valid builtin signature. 26 */ 27 static int fsverity_require_signatures; 28 29 /* 30 * Keyring that contains the trusted X.509 certificates. 31 * 32 * Only root (kuid=0) can modify this. Also, root may use 33 * keyctl_restrict_keyring() to prevent any more additions. 34 */ 35 static struct key *fsverity_keyring; 36 37 /** 38 * fsverity_verify_signature() - check a verity file's signature 39 * @vi: the file's fsverity_info 40 * @signature: the file's built-in signature 41 * @sig_size: size of signature in bytes, or 0 if no signature 42 * 43 * If the file includes a signature of its fs-verity file digest, verify it 44 * against the certificates in the fs-verity keyring. 45 * 46 * Return: 0 on success (signature valid or not required); -errno on failure 47 */ 48 int fsverity_verify_signature(const struct fsverity_info *vi, 49 const u8 *signature, size_t sig_size) 50 { 51 const struct inode *inode = vi->inode; 52 const struct fsverity_hash_alg *hash_alg = vi->tree_params.hash_alg; 53 struct fsverity_formatted_digest *d; 54 int err; 55 56 if (sig_size == 0) { 57 if (fsverity_require_signatures) { 58 fsverity_err(inode, 59 "require_signatures=1, rejecting unsigned file!"); 60 return -EPERM; 61 } 62 return 0; 63 } 64 65 d = kzalloc(sizeof(*d) + hash_alg->digest_size, GFP_KERNEL); 66 if (!d) 67 return -ENOMEM; 68 memcpy(d->magic, "FSVerity", 8); 69 d->digest_algorithm = cpu_to_le16(hash_alg - fsverity_hash_algs); 70 d->digest_size = cpu_to_le16(hash_alg->digest_size); 71 memcpy(d->digest, vi->file_digest, hash_alg->digest_size); 72 73 err = verify_pkcs7_signature(d, sizeof(*d) + hash_alg->digest_size, 74 signature, sig_size, fsverity_keyring, 75 VERIFYING_UNSPECIFIED_SIGNATURE, 76 NULL, NULL); 77 kfree(d); 78 79 if (err) { 80 if (err == -ENOKEY) 81 fsverity_err(inode, 82 "File's signing cert isn't in the fs-verity keyring"); 83 else if (err == -EKEYREJECTED) 84 fsverity_err(inode, "Incorrect file signature"); 85 else if (err == -EBADMSG) 86 fsverity_err(inode, "Malformed file signature"); 87 else 88 fsverity_err(inode, "Error %d verifying file signature", 89 err); 90 return err; 91 } 92 93 return 0; 94 } 95 96 #ifdef CONFIG_SYSCTL 97 static struct ctl_table_header *fsverity_sysctl_header; 98 99 static struct ctl_table fsverity_sysctl_table[] = { 100 { 101 .procname = "require_signatures", 102 .data = &fsverity_require_signatures, 103 .maxlen = sizeof(int), 104 .mode = 0644, 105 .proc_handler = proc_dointvec_minmax, 106 .extra1 = SYSCTL_ZERO, 107 .extra2 = SYSCTL_ONE, 108 }, 109 { } 110 }; 111 112 static int __init fsverity_sysctl_init(void) 113 { 114 fsverity_sysctl_header = register_sysctl("fs/verity", fsverity_sysctl_table); 115 if (!fsverity_sysctl_header) { 116 pr_err("sysctl registration failed!\n"); 117 return -ENOMEM; 118 } 119 return 0; 120 } 121 #else /* !CONFIG_SYSCTL */ 122 static inline int __init fsverity_sysctl_init(void) 123 { 124 return 0; 125 } 126 #endif /* !CONFIG_SYSCTL */ 127 128 int __init fsverity_init_signature(void) 129 { 130 struct key *ring; 131 int err; 132 133 ring = keyring_alloc(".fs-verity", KUIDT_INIT(0), KGIDT_INIT(0), 134 current_cred(), KEY_POS_SEARCH | 135 KEY_USR_VIEW | KEY_USR_READ | KEY_USR_WRITE | 136 KEY_USR_SEARCH | KEY_USR_SETATTR, 137 KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL); 138 if (IS_ERR(ring)) 139 return PTR_ERR(ring); 140 141 err = fsverity_sysctl_init(); 142 if (err) 143 goto err_put_ring; 144 145 fsverity_keyring = ring; 146 return 0; 147 148 err_put_ring: 149 key_put(ring); 150 return err; 151 } 152