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328 lines
9.0 KiB
328 lines
9.0 KiB
// SPDX-License-Identifier: GPL-2.0 |
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/* |
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* fs-verity hash algorithms |
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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 <crypto/hash.h> |
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#include <linux/scatterlist.h> |
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/* The hash algorithms supported by fs-verity */ |
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struct fsverity_hash_alg fsverity_hash_algs[] = { |
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[FS_VERITY_HASH_ALG_SHA256] = { |
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.name = "sha256", |
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.digest_size = SHA256_DIGEST_SIZE, |
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.block_size = SHA256_BLOCK_SIZE, |
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}, |
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[FS_VERITY_HASH_ALG_SHA512] = { |
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.name = "sha512", |
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.digest_size = SHA512_DIGEST_SIZE, |
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.block_size = SHA512_BLOCK_SIZE, |
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}, |
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}; |
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static DEFINE_MUTEX(fsverity_hash_alg_init_mutex); |
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/** |
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* fsverity_get_hash_alg() - validate and prepare a hash algorithm |
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* @inode: optional inode for logging purposes |
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* @num: the hash algorithm number |
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* |
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* Get the struct fsverity_hash_alg for the given hash algorithm number, and |
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* ensure it has a hash transform ready to go. The hash transforms are |
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* allocated on-demand so that we don't waste resources unnecessarily, and |
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* because the crypto modules may be initialized later than fs/verity/. |
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* |
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* Return: pointer to the hash alg on success, else an ERR_PTR() |
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*/ |
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struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode, |
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unsigned int num) |
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{ |
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struct fsverity_hash_alg *alg; |
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struct crypto_ahash *tfm; |
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int err; |
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if (num >= ARRAY_SIZE(fsverity_hash_algs) || |
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!fsverity_hash_algs[num].name) { |
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fsverity_warn(inode, "Unknown hash algorithm number: %u", num); |
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return ERR_PTR(-EINVAL); |
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} |
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alg = &fsverity_hash_algs[num]; |
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/* pairs with smp_store_release() below */ |
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if (likely(smp_load_acquire(&alg->tfm) != NULL)) |
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return alg; |
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mutex_lock(&fsverity_hash_alg_init_mutex); |
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if (alg->tfm != NULL) |
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goto out_unlock; |
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/* |
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* Using the shash API would make things a bit simpler, but the ahash |
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* API is preferable as it allows the use of crypto accelerators. |
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*/ |
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tfm = crypto_alloc_ahash(alg->name, 0, 0); |
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if (IS_ERR(tfm)) { |
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if (PTR_ERR(tfm) == -ENOENT) { |
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fsverity_warn(inode, |
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"Missing crypto API support for hash algorithm \"%s\"", |
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alg->name); |
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alg = ERR_PTR(-ENOPKG); |
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goto out_unlock; |
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} |
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fsverity_err(inode, |
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"Error allocating hash algorithm \"%s\": %ld", |
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alg->name, PTR_ERR(tfm)); |
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alg = ERR_CAST(tfm); |
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goto out_unlock; |
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} |
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err = -EINVAL; |
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if (WARN_ON(alg->digest_size != crypto_ahash_digestsize(tfm))) |
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goto err_free_tfm; |
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if (WARN_ON(alg->block_size != crypto_ahash_blocksize(tfm))) |
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goto err_free_tfm; |
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err = mempool_init_kmalloc_pool(&alg->req_pool, 1, |
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sizeof(struct ahash_request) + |
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crypto_ahash_reqsize(tfm)); |
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if (err) |
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goto err_free_tfm; |
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pr_info("%s using implementation \"%s\"\n", |
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alg->name, crypto_ahash_driver_name(tfm)); |
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/* pairs with smp_load_acquire() above */ |
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smp_store_release(&alg->tfm, tfm); |
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goto out_unlock; |
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err_free_tfm: |
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crypto_free_ahash(tfm); |
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alg = ERR_PTR(err); |
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out_unlock: |
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mutex_unlock(&fsverity_hash_alg_init_mutex); |
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return alg; |
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} |
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/** |
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* fsverity_alloc_hash_request() - allocate a hash request object |
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* @alg: the hash algorithm for which to allocate the request |
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* @gfp_flags: memory allocation flags |
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* |
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* This is mempool-backed, so this never fails if __GFP_DIRECT_RECLAIM is set in |
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* @gfp_flags. However, in that case this might need to wait for all |
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* previously-allocated requests to be freed. So to avoid deadlocks, callers |
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* must never need multiple requests at a time to make forward progress. |
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* |
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* Return: the request object on success; NULL on failure (but see above) |
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*/ |
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struct ahash_request *fsverity_alloc_hash_request(struct fsverity_hash_alg *alg, |
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gfp_t gfp_flags) |
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{ |
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struct ahash_request *req = mempool_alloc(&alg->req_pool, gfp_flags); |
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if (req) |
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ahash_request_set_tfm(req, alg->tfm); |
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return req; |
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} |
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/** |
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* fsverity_free_hash_request() - free a hash request object |
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* @alg: the hash algorithm |
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* @req: the hash request object to free |
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*/ |
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void fsverity_free_hash_request(struct fsverity_hash_alg *alg, |
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struct ahash_request *req) |
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{ |
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if (req) { |
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ahash_request_zero(req); |
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mempool_free(req, &alg->req_pool); |
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} |
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} |
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/** |
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* fsverity_prepare_hash_state() - precompute the initial hash state |
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* @alg: hash algorithm |
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* @salt: a salt which is to be prepended to all data to be hashed |
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* @salt_size: salt size in bytes, possibly 0 |
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* |
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* Return: NULL if the salt is empty, otherwise the kmalloc()'ed precomputed |
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* initial hash state on success or an ERR_PTR() on failure. |
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*/ |
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const u8 *fsverity_prepare_hash_state(struct fsverity_hash_alg *alg, |
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const u8 *salt, size_t salt_size) |
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{ |
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u8 *hashstate = NULL; |
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struct ahash_request *req = NULL; |
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u8 *padded_salt = NULL; |
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size_t padded_salt_size; |
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struct scatterlist sg; |
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DECLARE_CRYPTO_WAIT(wait); |
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int err; |
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if (salt_size == 0) |
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return NULL; |
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hashstate = kmalloc(crypto_ahash_statesize(alg->tfm), GFP_KERNEL); |
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if (!hashstate) |
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return ERR_PTR(-ENOMEM); |
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/* This allocation never fails, since it's mempool-backed. */ |
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req = fsverity_alloc_hash_request(alg, GFP_KERNEL); |
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/* |
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* Zero-pad the salt to the next multiple of the input size of the hash |
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* algorithm's compression function, e.g. 64 bytes for SHA-256 or 128 |
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* bytes for SHA-512. This ensures that the hash algorithm won't have |
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* any bytes buffered internally after processing the salt, thus making |
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* salted hashing just as fast as unsalted hashing. |
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*/ |
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padded_salt_size = round_up(salt_size, alg->block_size); |
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padded_salt = kzalloc(padded_salt_size, GFP_KERNEL); |
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if (!padded_salt) { |
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err = -ENOMEM; |
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goto err_free; |
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} |
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memcpy(padded_salt, salt, salt_size); |
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sg_init_one(&sg, padded_salt, padded_salt_size); |
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ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP | |
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CRYPTO_TFM_REQ_MAY_BACKLOG, |
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crypto_req_done, &wait); |
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ahash_request_set_crypt(req, &sg, NULL, padded_salt_size); |
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err = crypto_wait_req(crypto_ahash_init(req), &wait); |
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if (err) |
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goto err_free; |
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err = crypto_wait_req(crypto_ahash_update(req), &wait); |
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if (err) |
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goto err_free; |
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err = crypto_ahash_export(req, hashstate); |
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if (err) |
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goto err_free; |
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out: |
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fsverity_free_hash_request(alg, req); |
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kfree(padded_salt); |
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return hashstate; |
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err_free: |
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kfree(hashstate); |
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hashstate = ERR_PTR(err); |
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goto out; |
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} |
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/** |
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* fsverity_hash_page() - hash a single data or hash page |
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* @params: the Merkle tree's parameters |
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* @inode: inode for which the hashing is being done |
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* @req: preallocated hash request |
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* @page: the page to hash |
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* @out: output digest, size 'params->digest_size' bytes |
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* |
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* Hash a single data or hash block, assuming block_size == PAGE_SIZE. |
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* The hash is salted if a salt is specified in the Merkle tree parameters. |
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* |
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* Return: 0 on success, -errno on failure |
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*/ |
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int fsverity_hash_page(const struct merkle_tree_params *params, |
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const struct inode *inode, |
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struct ahash_request *req, struct page *page, u8 *out) |
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{ |
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struct scatterlist sg; |
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DECLARE_CRYPTO_WAIT(wait); |
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int err; |
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if (WARN_ON(params->block_size != PAGE_SIZE)) |
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return -EINVAL; |
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sg_init_table(&sg, 1); |
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sg_set_page(&sg, page, PAGE_SIZE, 0); |
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ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP | |
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CRYPTO_TFM_REQ_MAY_BACKLOG, |
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crypto_req_done, &wait); |
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ahash_request_set_crypt(req, &sg, out, PAGE_SIZE); |
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if (params->hashstate) { |
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err = crypto_ahash_import(req, params->hashstate); |
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if (err) { |
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fsverity_err(inode, |
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"Error %d importing hash state", err); |
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return err; |
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} |
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err = crypto_ahash_finup(req); |
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} else { |
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err = crypto_ahash_digest(req); |
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} |
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err = crypto_wait_req(err, &wait); |
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if (err) |
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fsverity_err(inode, "Error %d computing page hash", err); |
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return err; |
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} |
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/** |
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* fsverity_hash_buffer() - hash some data |
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* @alg: the hash algorithm to use |
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* @data: the data to hash |
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* @size: size of data to hash, in bytes |
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* @out: output digest, size 'alg->digest_size' bytes |
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* |
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* Hash some data which is located in physically contiguous memory (i.e. memory |
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* allocated by kmalloc(), not by vmalloc()). No salt is used. |
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* |
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* Return: 0 on success, -errno on failure |
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*/ |
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int fsverity_hash_buffer(struct fsverity_hash_alg *alg, |
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const void *data, size_t size, u8 *out) |
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{ |
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struct ahash_request *req; |
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struct scatterlist sg; |
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DECLARE_CRYPTO_WAIT(wait); |
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int err; |
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/* This allocation never fails, since it's mempool-backed. */ |
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req = fsverity_alloc_hash_request(alg, GFP_KERNEL); |
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sg_init_one(&sg, data, size); |
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ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP | |
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CRYPTO_TFM_REQ_MAY_BACKLOG, |
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crypto_req_done, &wait); |
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ahash_request_set_crypt(req, &sg, out, size); |
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err = crypto_wait_req(crypto_ahash_digest(req), &wait); |
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fsverity_free_hash_request(alg, req); |
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return err; |
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} |
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void __init fsverity_check_hash_algs(void) |
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{ |
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size_t i; |
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/* |
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* Sanity check the hash algorithms (could be a build-time check, but |
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* they're in an array) |
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*/ |
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for (i = 0; i < ARRAY_SIZE(fsverity_hash_algs); i++) { |
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const struct fsverity_hash_alg *alg = &fsverity_hash_algs[i]; |
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if (!alg->name) |
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continue; |
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BUG_ON(alg->digest_size > FS_VERITY_MAX_DIGEST_SIZE); |
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/* |
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* For efficiency, the implementation currently assumes the |
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* digest and block sizes are powers of 2. This limitation can |
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* be lifted if the code is updated to handle other values. |
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*/ |
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BUG_ON(!is_power_of_2(alg->digest_size)); |
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BUG_ON(!is_power_of_2(alg->block_size)); |
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} |
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}
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