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![Eric Biggers](/assets/img/avatar_default.png)
If the file size is almost S64_MAX, the calculated number of Merkle tree levels exceeds FS_VERITY_MAX_LEVELS, causing FS_IOC_ENABLE_VERITY to fail. This is unintentional, since as the comment above the definition of FS_VERITY_MAX_LEVELS states, it is enough for over U64_MAX bytes of data using SHA-256 and 4K blocks. (Specifically, 4096*128**8 >= 2**64.) The bug is actually that when the number of blocks in the first level is calculated from i_size, there is a signed integer overflow due to i_size being signed. Fix this by treating i_size as unsigned. This was found by the new test "generic: test fs-verity EFBIG scenarios" (https://lkml.kernel.org/r/b1d116cd4d0ea74b9cd86f349c672021e005a75c.1631558495.git.boris@bur.io). This didn't affect ext4 or f2fs since those have a smaller maximum file size, but it did affect btrfs which allows files up to S64_MAX bytes. Reported-by: Boris Burkov <boris@bur.io> Fixes:3fda4c617e
("fs-verity: implement FS_IOC_ENABLE_VERITY ioctl") Fixes:fd2d1acfca
("fs-verity: add the hook for file ->open()") Cc: <stable@vger.kernel.org> # v5.4+ Reviewed-by: Boris Burkov <boris@bur.io> Link: https://lore.kernel.org/r/20210916203424.113376-1-ebiggers@kernel.org Signed-off-by: Eric Biggers <ebiggers@google.com>
408 lines
11 KiB
C
408 lines
11 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Opening fs-verity files
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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/slab.h>
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static struct kmem_cache *fsverity_info_cachep;
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/**
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* fsverity_init_merkle_tree_params() - initialize Merkle tree parameters
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* @params: the parameters struct to initialize
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* @inode: the inode for which the Merkle tree is being built
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* @hash_algorithm: number of hash algorithm to use
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* @log_blocksize: log base 2 of block size to use
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* @salt: pointer to salt (optional)
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* @salt_size: size of salt, possibly 0
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*
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* Validate the hash algorithm and block size, then compute the tree topology
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* (num levels, num blocks in each level, etc.) and initialize @params.
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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_init_merkle_tree_params(struct merkle_tree_params *params,
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const struct inode *inode,
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unsigned int hash_algorithm,
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unsigned int log_blocksize,
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const u8 *salt, size_t salt_size)
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{
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struct fsverity_hash_alg *hash_alg;
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int err;
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u64 blocks;
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u64 offset;
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int level;
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memset(params, 0, sizeof(*params));
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hash_alg = fsverity_get_hash_alg(inode, hash_algorithm);
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if (IS_ERR(hash_alg))
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return PTR_ERR(hash_alg);
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params->hash_alg = hash_alg;
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params->digest_size = hash_alg->digest_size;
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params->hashstate = fsverity_prepare_hash_state(hash_alg, salt,
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salt_size);
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if (IS_ERR(params->hashstate)) {
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err = PTR_ERR(params->hashstate);
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params->hashstate = NULL;
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fsverity_err(inode, "Error %d preparing hash state", err);
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goto out_err;
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}
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if (log_blocksize != PAGE_SHIFT) {
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fsverity_warn(inode, "Unsupported log_blocksize: %u",
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log_blocksize);
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err = -EINVAL;
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goto out_err;
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}
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params->log_blocksize = log_blocksize;
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params->block_size = 1 << log_blocksize;
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if (WARN_ON(!is_power_of_2(params->digest_size))) {
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err = -EINVAL;
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goto out_err;
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}
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if (params->block_size < 2 * params->digest_size) {
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fsverity_warn(inode,
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"Merkle tree block size (%u) too small for hash algorithm \"%s\"",
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params->block_size, hash_alg->name);
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err = -EINVAL;
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goto out_err;
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}
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params->log_arity = params->log_blocksize - ilog2(params->digest_size);
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params->hashes_per_block = 1 << params->log_arity;
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pr_debug("Merkle tree uses %s with %u-byte blocks (%u hashes/block), salt=%*phN\n",
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hash_alg->name, params->block_size, params->hashes_per_block,
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(int)salt_size, salt);
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/*
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* Compute the number of levels in the Merkle tree and create a map from
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* level to the starting block of that level. Level 'num_levels - 1' is
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* the root and is stored first. Level 0 is the level directly "above"
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* the data blocks and is stored last.
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*/
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/* Compute number of levels and the number of blocks in each level */
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blocks = ((u64)inode->i_size + params->block_size - 1) >> log_blocksize;
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pr_debug("Data is %lld bytes (%llu blocks)\n", inode->i_size, blocks);
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while (blocks > 1) {
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if (params->num_levels >= FS_VERITY_MAX_LEVELS) {
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fsverity_err(inode, "Too many levels in Merkle tree");
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err = -EINVAL;
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goto out_err;
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}
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blocks = (blocks + params->hashes_per_block - 1) >>
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params->log_arity;
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/* temporarily using level_start[] to store blocks in level */
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params->level_start[params->num_levels++] = blocks;
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}
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params->level0_blocks = params->level_start[0];
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/* Compute the starting block of each level */
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offset = 0;
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for (level = (int)params->num_levels - 1; level >= 0; level--) {
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blocks = params->level_start[level];
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params->level_start[level] = offset;
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pr_debug("Level %d is %llu blocks starting at index %llu\n",
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level, blocks, offset);
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offset += blocks;
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}
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params->tree_size = offset << log_blocksize;
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return 0;
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out_err:
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kfree(params->hashstate);
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memset(params, 0, sizeof(*params));
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return err;
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}
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/*
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* Compute the file digest by hashing the fsverity_descriptor excluding the
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* signature and with the sig_size field set to 0.
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*/
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static int compute_file_digest(struct fsverity_hash_alg *hash_alg,
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struct fsverity_descriptor *desc,
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u8 *file_digest)
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{
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__le32 sig_size = desc->sig_size;
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int err;
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desc->sig_size = 0;
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err = fsverity_hash_buffer(hash_alg, desc, sizeof(*desc), file_digest);
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desc->sig_size = sig_size;
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return err;
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}
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/*
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* Create a new fsverity_info from the given fsverity_descriptor (with optional
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* appended signature), and check the signature if present. The
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* fsverity_descriptor must have already undergone basic validation.
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*/
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struct fsverity_info *fsverity_create_info(const struct inode *inode,
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struct fsverity_descriptor *desc,
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size_t desc_size)
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{
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struct fsverity_info *vi;
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int err;
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vi = kmem_cache_zalloc(fsverity_info_cachep, GFP_KERNEL);
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if (!vi)
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return ERR_PTR(-ENOMEM);
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vi->inode = inode;
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err = fsverity_init_merkle_tree_params(&vi->tree_params, inode,
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desc->hash_algorithm,
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desc->log_blocksize,
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desc->salt, desc->salt_size);
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if (err) {
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fsverity_err(inode,
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"Error %d initializing Merkle tree parameters",
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err);
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goto out;
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}
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memcpy(vi->root_hash, desc->root_hash, vi->tree_params.digest_size);
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err = compute_file_digest(vi->tree_params.hash_alg, desc,
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vi->file_digest);
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if (err) {
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fsverity_err(inode, "Error %d computing file digest", err);
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goto out;
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}
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pr_debug("Computed file digest: %s:%*phN\n",
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vi->tree_params.hash_alg->name,
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vi->tree_params.digest_size, vi->file_digest);
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err = fsverity_verify_signature(vi, desc->signature,
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le32_to_cpu(desc->sig_size));
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out:
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if (err) {
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fsverity_free_info(vi);
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vi = ERR_PTR(err);
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}
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return vi;
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}
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void fsverity_set_info(struct inode *inode, struct fsverity_info *vi)
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{
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/*
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* Multiple tasks may race to set ->i_verity_info, so use
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* cmpxchg_release(). This pairs with the smp_load_acquire() in
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* fsverity_get_info(). I.e., here we publish ->i_verity_info with a
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* RELEASE barrier so that other tasks can ACQUIRE it.
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*/
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if (cmpxchg_release(&inode->i_verity_info, NULL, vi) != NULL) {
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/* Lost the race, so free the fsverity_info we allocated. */
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fsverity_free_info(vi);
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/*
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* Afterwards, the caller may access ->i_verity_info directly,
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* so make sure to ACQUIRE the winning fsverity_info.
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*/
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(void)fsverity_get_info(inode);
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}
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}
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void fsverity_free_info(struct fsverity_info *vi)
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{
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if (!vi)
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return;
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kfree(vi->tree_params.hashstate);
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kmem_cache_free(fsverity_info_cachep, vi);
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}
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static bool validate_fsverity_descriptor(struct inode *inode,
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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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if (desc_size < sizeof(*desc)) {
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fsverity_err(inode, "Unrecognized descriptor size: %zu bytes",
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desc_size);
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return false;
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}
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if (desc->version != 1) {
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fsverity_err(inode, "Unrecognized descriptor version: %u",
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desc->version);
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return false;
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}
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if (memchr_inv(desc->__reserved, 0, sizeof(desc->__reserved))) {
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fsverity_err(inode, "Reserved bits set in descriptor");
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return false;
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}
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if (desc->salt_size > sizeof(desc->salt)) {
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fsverity_err(inode, "Invalid salt_size: %u", desc->salt_size);
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return false;
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}
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if (le64_to_cpu(desc->data_size) != inode->i_size) {
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fsverity_err(inode,
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"Wrong data_size: %llu (desc) != %lld (inode)",
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le64_to_cpu(desc->data_size), inode->i_size);
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return false;
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}
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if (le32_to_cpu(desc->sig_size) > desc_size - sizeof(*desc)) {
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fsverity_err(inode, "Signature overflows verity descriptor");
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return false;
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}
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return true;
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}
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/*
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* Read the inode's fsverity_descriptor (with optional appended signature) from
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* the filesystem, and do basic validation of it.
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*/
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int fsverity_get_descriptor(struct inode *inode,
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struct fsverity_descriptor **desc_ret,
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size_t *desc_size_ret)
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{
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int res;
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struct fsverity_descriptor *desc;
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res = inode->i_sb->s_vop->get_verity_descriptor(inode, NULL, 0);
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if (res < 0) {
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fsverity_err(inode,
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"Error %d getting verity descriptor size", res);
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return res;
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}
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if (res > FS_VERITY_MAX_DESCRIPTOR_SIZE) {
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fsverity_err(inode, "Verity descriptor is too large (%d bytes)",
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res);
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return -EMSGSIZE;
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}
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desc = kmalloc(res, GFP_KERNEL);
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if (!desc)
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return -ENOMEM;
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res = inode->i_sb->s_vop->get_verity_descriptor(inode, desc, res);
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if (res < 0) {
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fsverity_err(inode, "Error %d reading verity descriptor", res);
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kfree(desc);
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return res;
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}
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if (!validate_fsverity_descriptor(inode, desc, res)) {
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kfree(desc);
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return -EINVAL;
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}
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*desc_ret = desc;
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*desc_size_ret = res;
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return 0;
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}
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/* Ensure the inode has an ->i_verity_info */
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static int ensure_verity_info(struct inode *inode)
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{
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struct fsverity_info *vi = fsverity_get_info(inode);
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struct fsverity_descriptor *desc;
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size_t desc_size;
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int err;
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if (vi)
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return 0;
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err = fsverity_get_descriptor(inode, &desc, &desc_size);
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if (err)
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return err;
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vi = fsverity_create_info(inode, desc, desc_size);
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if (IS_ERR(vi)) {
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err = PTR_ERR(vi);
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goto out_free_desc;
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}
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fsverity_set_info(inode, vi);
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err = 0;
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out_free_desc:
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kfree(desc);
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return err;
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}
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/**
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* fsverity_file_open() - prepare to open a verity file
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* @inode: the inode being opened
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* @filp: the struct file being set up
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*
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* When opening a verity file, deny the open if it is for writing. Otherwise,
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* set up the inode's ->i_verity_info if not already done.
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*
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* When combined with fscrypt, this must be called after fscrypt_file_open().
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* Otherwise, we won't have the key set up to decrypt the verity metadata.
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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_file_open(struct inode *inode, struct file *filp)
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{
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if (!IS_VERITY(inode))
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return 0;
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if (filp->f_mode & FMODE_WRITE) {
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pr_debug("Denying opening verity file (ino %lu) for write\n",
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inode->i_ino);
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return -EPERM;
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}
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return ensure_verity_info(inode);
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}
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EXPORT_SYMBOL_GPL(fsverity_file_open);
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/**
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* fsverity_prepare_setattr() - prepare to change a verity inode's attributes
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* @dentry: dentry through which the inode is being changed
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* @attr: attributes to change
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*
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* Verity files are immutable, so deny truncates. This isn't covered by the
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* open-time check because sys_truncate() takes a path, not a file descriptor.
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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_prepare_setattr(struct dentry *dentry, struct iattr *attr)
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{
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if (IS_VERITY(d_inode(dentry)) && (attr->ia_valid & ATTR_SIZE)) {
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pr_debug("Denying truncate of verity file (ino %lu)\n",
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d_inode(dentry)->i_ino);
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return -EPERM;
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}
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return 0;
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}
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EXPORT_SYMBOL_GPL(fsverity_prepare_setattr);
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/**
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* fsverity_cleanup_inode() - free the inode's verity info, if present
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* @inode: an inode being evicted
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*
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* Filesystems must call this on inode eviction to free ->i_verity_info.
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*/
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void fsverity_cleanup_inode(struct inode *inode)
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{
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fsverity_free_info(inode->i_verity_info);
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inode->i_verity_info = NULL;
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}
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EXPORT_SYMBOL_GPL(fsverity_cleanup_inode);
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int __init fsverity_init_info_cache(void)
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{
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fsverity_info_cachep = KMEM_CACHE_USERCOPY(fsverity_info,
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SLAB_RECLAIM_ACCOUNT,
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file_digest);
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if (!fsverity_info_cachep)
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return -ENOMEM;
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return 0;
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}
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void __init fsverity_exit_info_cache(void)
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{
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kmem_cache_destroy(fsverity_info_cachep);
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fsverity_info_cachep = NULL;
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}
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