// SPDX-License-Identifier: GPL-2.0
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/*
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* Verification of builtin signatures
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*
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* Copyright 2019 Google LLC
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*/
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#include "fsverity_private.h"
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#include <linux/cred.h>
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#include <linux/key.h>
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#include <linux/slab.h>
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#include <linux/verification.h>
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/*
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* /proc/sys/fs/verity/require_signatures
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* If 1, all verity files must have a valid builtin signature.
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*/
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static int fsverity_require_signatures;
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/*
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* Keyring that contains the trusted X.509 certificates.
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*
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* Only root (kuid=0) can modify this. Also, root may use
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* keyctl_restrict_keyring() to prevent any more additions.
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*/
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static struct key *fsverity_keyring;
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/**
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* __fsverity_verify_signature() - check a verity file's signature
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* @inode: the file's inode
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* @signature: the file's signature
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* @sig_size: size of @signature. Can be 0 if there is no signature
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* @file_digest: the file's digest
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* @digest_algorithm: the digest algorithm used
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*
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* Takes the file's digest and optional signature and verifies the signature
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* against the digest and the fs-verity keyring if appropriate
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*
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* Return: 0 on success (signature valid or not required); -errno on failure
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*/
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int __fsverity_verify_signature(const struct inode *inode, const u8 *signature,
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u32 sig_size, const u8 *file_digest,
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unsigned int digest_algorithm)
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{
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struct fsverity_formatted_digest *d;
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struct fsverity_hash_alg *hash_alg = fsverity_get_hash_alg(inode,
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digest_algorithm);
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int err;
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if (IS_ERR(hash_alg))
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return PTR_ERR(hash_alg);
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if (sig_size == 0) {
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if (fsverity_require_signatures) {
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fsverity_err(inode,
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"require_signatures=1, rejecting unsigned file!");
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return -EPERM;
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}
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return 0;
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}
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d = kzalloc(sizeof(*d) + hash_alg->digest_size, GFP_KERNEL);
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if (!d)
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return -ENOMEM;
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memcpy(d->magic, "FSVerity", 8);
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d->digest_algorithm = cpu_to_le16(hash_alg - fsverity_hash_algs);
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d->digest_size = cpu_to_le16(hash_alg->digest_size);
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memcpy(d->digest, file_digest, hash_alg->digest_size);
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err = verify_pkcs7_signature(d, sizeof(*d) + hash_alg->digest_size,
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signature, sig_size,
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fsverity_keyring,
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VERIFYING_UNSPECIFIED_SIGNATURE,
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NULL, NULL);
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kfree(d);
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if (err) {
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if (err == -ENOKEY)
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fsverity_err(inode,
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"File's signing cert isn't in the fs-verity keyring");
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else if (err == -EKEYREJECTED)
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fsverity_err(inode, "Incorrect file signature");
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else if (err == -EBADMSG)
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fsverity_err(inode, "Malformed file signature");
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else
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fsverity_err(inode, "Error %d verifying file signature",
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err);
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return err;
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}
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pr_debug("Valid signature for file digest %s:%*phN\n",
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hash_alg->name, hash_alg->digest_size, file_digest);
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return 0;
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}
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EXPORT_SYMBOL_GPL(__fsverity_verify_signature);
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/**
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* fsverity_verify_signature() - check a verity file's signature
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* @vi: the file's fsverity_info
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* @desc: the file's fsverity_descriptor
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* @desc_size: size of @desc
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*
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* If the file's fs-verity descriptor includes a signature of the file digest,
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* verify it against the certificates in the fs-verity keyring.
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*
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* Return: 0 on success (signature valid or not required); -errno on failure
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*/
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int fsverity_verify_signature(const struct fsverity_info *vi,
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const struct fsverity_descriptor *desc,
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size_t desc_size)
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{
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const struct inode *inode = vi->inode;
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const struct fsverity_hash_alg *hash_alg = vi->tree_params.hash_alg;
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const u32 sig_size = le32_to_cpu(desc->sig_size);
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if (sig_size > desc_size - sizeof(*desc)) {
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fsverity_err(inode, "Signature overflows verity descriptor");
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return -EBADMSG;
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}
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return __fsverity_verify_signature(inode, desc->signature, sig_size,
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vi->file_digest, hash_alg - fsverity_hash_algs);
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}
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#ifdef CONFIG_SYSCTL
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static struct ctl_table_header *fsverity_sysctl_header;
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static const struct ctl_path fsverity_sysctl_path[] = {
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{ .procname = "fs", },
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{ .procname = "verity", },
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{ }
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};
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/* shared constants to be used in various sysctls */
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static int sysctl_vals[] = { 0, 1, INT_MAX };
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#define SYSCTL_ZERO ((void *)&sysctl_vals[0])
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#define SYSCTL_ONE ((void *)&sysctl_vals[1])
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#define SYSCTL_INT_MAX ((void *)&sysctl_vals[2])
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static struct ctl_table fsverity_sysctl_table[] = {
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{
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.procname = "require_signatures",
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.data = &fsverity_require_signatures,
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.maxlen = sizeof(int),
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.mode = 0644,
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.proc_handler = proc_dointvec_minmax,
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.extra1 = SYSCTL_ZERO,
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.extra2 = SYSCTL_ONE,
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},
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{ }
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};
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static int __init fsverity_sysctl_init(void)
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{
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fsverity_sysctl_header = register_sysctl_paths(fsverity_sysctl_path,
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fsverity_sysctl_table);
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if (!fsverity_sysctl_header) {
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pr_err("sysctl registration failed!\n");
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return -ENOMEM;
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}
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return 0;
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}
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#else /* !CONFIG_SYSCTL */
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static inline int __init fsverity_sysctl_init(void)
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{
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return 0;
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}
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#endif /* !CONFIG_SYSCTL */
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int __init fsverity_init_signature(void)
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{
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struct key *ring;
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int err;
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ring = keyring_alloc(".fs-verity", KUIDT_INIT(0), KGIDT_INIT(0),
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current_cred(), KEY_POS_SEARCH |
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KEY_USR_VIEW | KEY_USR_READ | KEY_USR_WRITE |
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KEY_USR_SEARCH | KEY_USR_SETATTR,
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KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL);
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if (IS_ERR(ring))
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return PTR_ERR(ring);
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err = fsverity_sysctl_init();
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if (err)
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goto err_put_ring;
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fsverity_keyring = ring;
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return 0;
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err_put_ring:
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key_put(ring);
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return err;
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}
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