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#include <linux/hck/lite_hck_code_sign.h> 23 24/* 25 * /proc/sys/fs/verity/require_signatures 26 * If 1, all verity files must have a valid builtin signature. 27 */ 28int fsverity_require_signatures; 29 30/* 31 * Keyring that contains the trusted X.509 certificates. 32 * 33 * Only root (kuid=0) can modify this. Also, root may use 34 * keyctl_restrict_keyring() to prevent any more additions. 35 */ 36static struct key *fsverity_keyring; 37 38#ifdef CONFIG_SECURITY_CODE_SIGN 39 40void fsverity_set_cert_type(struct fsverity_info *vi, 41 int cert_type) 42{ 43 vi->cert_type = cert_type; 44} 45 46int fsverity_get_cert_type(const struct inode *inode) 47{ 48 return fsverity_get_info(inode)->cert_type; 49} 50 51#else /* !CONFIG_SECURITY_CODE_SIGN */ 52 53static void inline fsverity_set_cert_type(struct fsverity_info *verity_info, 54 int cert_type) 55{ 56} 57 58#endif 59 60static inline int fsverity_verify_certchain(struct fsverity_info *vi, 61 const void *raw_pkcs7, size_t pkcs7_len) 62{ 63 int ret = 0; 64 65 CALL_HCK_LITE_HOOK(code_sign_verify_certchain_lhck, 66 raw_pkcs7, pkcs7_len, &vi->fcs_info, &ret); 67 if (ret > 0) { 68 fsverity_set_cert_type(vi, ret); 69 ret = 0; 70 } 71 72 return ret; 73} 74 75/** 76 * fsverity_verify_signature() - check a verity file's signature 77 * @vi: the file's fsverity_info 78 * @signature: the file's built-in signature 79 * @sig_size: size of signature in bytes, or 0 if no signature 80 * 81 * If the file includes a signature of its fs-verity file digest, verify it 82 * against the certificates in the fs-verity keyring. 83 * 84 * Return: 0 on success (signature valid or not required); -errno on failure 85 */ 86int fsverity_verify_signature(struct fsverity_info *vi, 87 const u8 *signature, size_t sig_size) 88{ 89 const struct inode *inode = vi->inode; 90 const struct fsverity_hash_alg *hash_alg = vi->tree_params.hash_alg; 91 struct fsverity_formatted_digest *d; 92 int err; 93 94 if (sig_size == 0) { 95 if (fsverity_require_signatures) { 96 fsverity_err(inode, 97 "require_signatures=1, rejecting unsigned file!"); 98 return -EPERM; 99 } 100 return 0; 101 } 102 103 if (fsverity_keyring->keys.nr_leaves_on_tree == 0) { 104 /* 105 * The ".fs-verity" keyring is empty, due to builtin signatures 106 * being supported by the kernel but not actually being used. 107 * In this case, verify_pkcs7_signature() would always return an 108 * error, usually ENOKEY. It could also be EBADMSG if the 109 * PKCS#7 is malformed, but that isn't very important to 110 * distinguish. So, just skip to ENOKEY to avoid the attack 111 * surface of the PKCS#7 parser, which would otherwise be 112 * reachable by any task able to execute FS_IOC_ENABLE_VERITY. 113 */ 114 fsverity_err(inode, 115 "fs-verity keyring is empty, rejecting signed file!"); 116 return -ENOKEY; 117 } 118 119 d = kzalloc(sizeof(*d) + hash_alg->digest_size, GFP_KERNEL); 120 if (!d) 121 return -ENOMEM; 122 memcpy(d->magic, "FSVerity", 8); 123 d->digest_algorithm = cpu_to_le16(hash_alg - fsverity_hash_algs); 124 d->digest_size = cpu_to_le16(hash_alg->digest_size); 125 memcpy(d->digest, vi->file_digest, hash_alg->digest_size); 126 127 err = fsverity_verify_certchain(vi, signature, sig_size); 128 if (err) { 129 fsverity_err(inode, "verify cert chain failed, err = %d", err); 130 return err; 131 } 132 pr_debug("verify cert chain success\n"); 133 134 err = verify_pkcs7_signature(d, sizeof(*d) + hash_alg->digest_size, 135 signature, sig_size, fsverity_keyring, 136 VERIFYING_UNSPECIFIED_SIGNATURE, 137 NULL, NULL); 138 kfree(d); 139 140 if (err) { 141 if (err == -ENOKEY) 142 fsverity_err(inode, 143 "File's signing cert isn't in the fs-verity keyring"); 144 else if (err == -EKEYREJECTED) 145 fsverity_err(inode, "Incorrect file signature"); 146 else if (err == -EBADMSG) 147 fsverity_err(inode, "Malformed file signature"); 148 else 149 fsverity_err(inode, "Error %d verifying file signature", 150 err); 151 return err; 152 } 153 154 return 0; 155} 156 157void __init fsverity_init_signature(void) 158{ 159 fsverity_keyring = 160 keyring_alloc(".fs-verity", KUIDT_INIT(0), KGIDT_INIT(0), 161 current_cred(), KEY_POS_SEARCH | 162 KEY_USR_VIEW | KEY_USR_READ | KEY_USR_WRITE | 163 KEY_USR_SEARCH | KEY_USR_SETATTR, 164 KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL); 165 if (IS_ERR(fsverity_keyring)) 166 panic("failed to allocate \".fs-verity\" keyring"); 167} 168