fs/verity/signature.c

   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         pr_debug("Valid signature for file digest %s:%*phN\n",
  86                  hash_alg->name, hash_alg->digest_size, vi->file_digest);
  87         return 0;
  88 }
  89
  90 #ifdef CONFIG_SYSCTL
  91 static struct ctl_table_header *fsverity_sysctl_header;
  92
  93 static const struct ctl_path fsverity_sysctl_path[] = {
  94         { .procname = "fs", },
  95         { .procname = "verity", },
  96         { }
  97 };
  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_paths(fsverity_sysctl_path,
 115                                                        fsverity_sysctl_table);
 116         if (!fsverity_sysctl_header) {
 117                 pr_err("sysctl registration failed!\n");
 118                 return -ENOMEM;
 119         }
 120         return 0;
 121 }
 122 #else /* !CONFIG_SYSCTL */
 123 static inline int __init fsverity_sysctl_init(void)
 124 {
 125         return 0;
 126 }
 127 #endif /* !CONFIG_SYSCTL */
 128
 129 int __init fsverity_init_signature(void)
 130 {
 131         struct key *ring;
 132         int err;
 133
 134         ring = keyring_alloc(".fs-verity", KUIDT_INIT(0), KGIDT_INIT(0),
 135                              current_cred(), KEY_POS_SEARCH |
 136                                 KEY_USR_VIEW | KEY_USR_READ | KEY_USR_WRITE |
 137                                 KEY_USR_SEARCH | KEY_USR_SETATTR,
 138                              KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
 139         if (IS_ERR(ring))
 140                 return PTR_ERR(ring);
 141
 142         err = fsverity_sysctl_init();
 143         if (err)
 144                 goto err_put_ring;
 145
 146         fsverity_keyring = ring;
 147         return 0;
 148
 149 err_put_ring:
 150         key_put(ring);
 151         return err;
 152 }