395 строки
11 KiB
C
395 строки
11 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Ioctl to enable verity on a file
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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/mount.h>
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#include <linux/pagemap.h>
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#include <linux/sched/signal.h>
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#include <linux/uaccess.h>
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struct block_buffer {
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u32 filled;
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u8 *data;
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};
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/* Hash a block, writing the result to the next level's pending block buffer. */
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static int hash_one_block(struct inode *inode,
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const struct merkle_tree_params *params,
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struct ahash_request *req, struct block_buffer *cur)
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{
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struct block_buffer *next = cur + 1;
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int err;
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/* Zero-pad the block if it's shorter than the block size. */
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memset(&cur->data[cur->filled], 0, params->block_size - cur->filled);
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err = fsverity_hash_block(params, inode, req, virt_to_page(cur->data),
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offset_in_page(cur->data),
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&next->data[next->filled]);
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if (err)
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return err;
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next->filled += params->digest_size;
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cur->filled = 0;
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return 0;
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}
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static int write_merkle_tree_block(struct inode *inode, const u8 *buf,
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unsigned long index,
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const struct merkle_tree_params *params)
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{
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u64 pos = (u64)index << params->log_blocksize;
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int err;
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err = inode->i_sb->s_vop->write_merkle_tree_block(inode, buf, pos,
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params->block_size);
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if (err)
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fsverity_err(inode, "Error %d writing Merkle tree block %lu",
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err, index);
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return err;
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}
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/*
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* Build the Merkle tree for the given file using the given parameters, and
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* return the root hash in @root_hash.
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*
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* The tree is written to a filesystem-specific location as determined by the
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* ->write_merkle_tree_block() method. However, the blocks that comprise the
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* tree are the same for all filesystems.
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*/
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static int build_merkle_tree(struct file *filp,
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const struct merkle_tree_params *params,
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u8 *root_hash)
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{
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struct inode *inode = file_inode(filp);
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const u64 data_size = inode->i_size;
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const int num_levels = params->num_levels;
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struct ahash_request *req;
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struct block_buffer _buffers[1 + FS_VERITY_MAX_LEVELS + 1] = {};
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struct block_buffer *buffers = &_buffers[1];
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unsigned long level_offset[FS_VERITY_MAX_LEVELS];
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int level;
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u64 offset;
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int err;
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if (data_size == 0) {
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/* Empty file is a special case; root hash is all 0's */
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memset(root_hash, 0, params->digest_size);
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return 0;
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}
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/* This allocation never fails, since it's mempool-backed. */
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req = fsverity_alloc_hash_request(params->hash_alg, GFP_KERNEL);
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/*
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* Allocate the block buffers. Buffer "-1" is for data blocks.
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* Buffers 0 <= level < num_levels are for the actual tree levels.
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* Buffer 'num_levels' is for the root hash.
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*/
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for (level = -1; level < num_levels; level++) {
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buffers[level].data = kzalloc(params->block_size, GFP_KERNEL);
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if (!buffers[level].data) {
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err = -ENOMEM;
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goto out;
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}
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}
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buffers[num_levels].data = root_hash;
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BUILD_BUG_ON(sizeof(level_offset) != sizeof(params->level_start));
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memcpy(level_offset, params->level_start, sizeof(level_offset));
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/* Hash each data block, also hashing the tree blocks as they fill up */
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for (offset = 0; offset < data_size; offset += params->block_size) {
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ssize_t bytes_read;
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loff_t pos = offset;
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buffers[-1].filled = min_t(u64, params->block_size,
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data_size - offset);
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bytes_read = __kernel_read(filp, buffers[-1].data,
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buffers[-1].filled, &pos);
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if (bytes_read < 0) {
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err = bytes_read;
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fsverity_err(inode, "Error %d reading file data", err);
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goto out;
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}
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if (bytes_read != buffers[-1].filled) {
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err = -EINVAL;
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fsverity_err(inode, "Short read of file data");
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goto out;
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}
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err = hash_one_block(inode, params, req, &buffers[-1]);
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if (err)
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goto out;
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for (level = 0; level < num_levels; level++) {
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if (buffers[level].filled + params->digest_size <=
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params->block_size) {
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/* Next block at @level isn't full yet */
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break;
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}
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/* Next block at @level is full */
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err = hash_one_block(inode, params, req,
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&buffers[level]);
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if (err)
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goto out;
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err = write_merkle_tree_block(inode,
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buffers[level].data,
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level_offset[level],
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params);
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if (err)
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goto out;
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level_offset[level]++;
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}
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if (fatal_signal_pending(current)) {
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err = -EINTR;
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goto out;
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}
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cond_resched();
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}
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/* Finish all nonempty pending tree blocks. */
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for (level = 0; level < num_levels; level++) {
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if (buffers[level].filled != 0) {
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err = hash_one_block(inode, params, req,
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&buffers[level]);
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if (err)
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goto out;
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err = write_merkle_tree_block(inode,
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buffers[level].data,
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level_offset[level],
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params);
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if (err)
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goto out;
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}
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}
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/* The root hash was filled by the last call to hash_one_block(). */
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if (WARN_ON(buffers[num_levels].filled != params->digest_size)) {
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err = -EINVAL;
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goto out;
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}
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err = 0;
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out:
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for (level = -1; level < num_levels; level++)
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kfree(buffers[level].data);
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fsverity_free_hash_request(params->hash_alg, req);
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return err;
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}
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static int enable_verity(struct file *filp,
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const struct fsverity_enable_arg *arg)
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{
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struct inode *inode = file_inode(filp);
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const struct fsverity_operations *vops = inode->i_sb->s_vop;
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struct merkle_tree_params params = { };
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struct fsverity_descriptor *desc;
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size_t desc_size = struct_size(desc, signature, arg->sig_size);
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struct fsverity_info *vi;
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int err;
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/* Start initializing the fsverity_descriptor */
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desc = kzalloc(desc_size, GFP_KERNEL);
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if (!desc)
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return -ENOMEM;
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desc->version = 1;
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desc->hash_algorithm = arg->hash_algorithm;
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desc->log_blocksize = ilog2(arg->block_size);
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/* Get the salt if the user provided one */
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if (arg->salt_size &&
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copy_from_user(desc->salt, u64_to_user_ptr(arg->salt_ptr),
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arg->salt_size)) {
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err = -EFAULT;
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goto out;
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}
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desc->salt_size = arg->salt_size;
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/* Get the signature if the user provided one */
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if (arg->sig_size &&
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copy_from_user(desc->signature, u64_to_user_ptr(arg->sig_ptr),
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arg->sig_size)) {
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err = -EFAULT;
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goto out;
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}
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desc->sig_size = cpu_to_le32(arg->sig_size);
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desc->data_size = cpu_to_le64(inode->i_size);
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/* Prepare the Merkle tree parameters */
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err = fsverity_init_merkle_tree_params(¶ms, inode,
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arg->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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goto out;
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/*
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* Start enabling verity on this file, serialized by the inode lock.
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* Fail if verity is already enabled or is already being enabled.
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*/
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inode_lock(inode);
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if (IS_VERITY(inode))
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err = -EEXIST;
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else
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err = vops->begin_enable_verity(filp);
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inode_unlock(inode);
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if (err)
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goto out;
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/*
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* Build the Merkle tree. Don't hold the inode lock during this, since
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* on huge files this may take a very long time and we don't want to
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* force unrelated syscalls like chown() to block forever. We don't
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* need the inode lock here because deny_write_access() already prevents
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* the file from being written to or truncated, and we still serialize
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* ->begin_enable_verity() and ->end_enable_verity() using the inode
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* lock and only allow one process to be here at a time on a given file.
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*/
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BUILD_BUG_ON(sizeof(desc->root_hash) < FS_VERITY_MAX_DIGEST_SIZE);
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err = build_merkle_tree(filp, ¶ms, desc->root_hash);
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if (err) {
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fsverity_err(inode, "Error %d building Merkle tree", err);
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goto rollback;
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}
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/*
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* Create the fsverity_info. Don't bother trying to save work by
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* reusing the merkle_tree_params from above. Instead, just create the
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* fsverity_info from the fsverity_descriptor as if it were just loaded
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* from disk. This is simpler, and it serves as an extra check that the
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* metadata we're writing is valid before actually enabling verity.
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*/
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vi = fsverity_create_info(inode, desc);
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if (IS_ERR(vi)) {
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err = PTR_ERR(vi);
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goto rollback;
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}
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/*
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* Tell the filesystem to finish enabling verity on the file.
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* Serialized with ->begin_enable_verity() by the inode lock.
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*/
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inode_lock(inode);
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err = vops->end_enable_verity(filp, desc, desc_size, params.tree_size);
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inode_unlock(inode);
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if (err) {
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fsverity_err(inode, "%ps() failed with err %d",
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vops->end_enable_verity, err);
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fsverity_free_info(vi);
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} else if (WARN_ON(!IS_VERITY(inode))) {
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err = -EINVAL;
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fsverity_free_info(vi);
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} else {
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/* Successfully enabled verity */
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/*
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* Readers can start using ->i_verity_info immediately, so it
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* can't be rolled back once set. So don't set it until just
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* after the filesystem has successfully enabled verity.
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*/
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fsverity_set_info(inode, vi);
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}
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out:
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kfree(params.hashstate);
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kfree(desc);
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return err;
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rollback:
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inode_lock(inode);
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(void)vops->end_enable_verity(filp, NULL, 0, params.tree_size);
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inode_unlock(inode);
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goto out;
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}
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/**
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* fsverity_ioctl_enable() - enable verity on a file
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* @filp: file to enable verity on
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* @uarg: user pointer to fsverity_enable_arg
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*
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* Enable fs-verity on a file. See the "FS_IOC_ENABLE_VERITY" section of
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* Documentation/filesystems/fsverity.rst for the documentation.
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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_ioctl_enable(struct file *filp, const void __user *uarg)
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{
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struct inode *inode = file_inode(filp);
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struct fsverity_enable_arg arg;
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int err;
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if (copy_from_user(&arg, uarg, sizeof(arg)))
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return -EFAULT;
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if (arg.version != 1)
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return -EINVAL;
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if (arg.__reserved1 ||
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memchr_inv(arg.__reserved2, 0, sizeof(arg.__reserved2)))
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return -EINVAL;
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if (!is_power_of_2(arg.block_size))
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return -EINVAL;
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if (arg.salt_size > sizeof_field(struct fsverity_descriptor, salt))
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return -EMSGSIZE;
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if (arg.sig_size > FS_VERITY_MAX_SIGNATURE_SIZE)
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return -EMSGSIZE;
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/*
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* Require a regular file with write access. But the actual fd must
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* still be readonly so that we can lock out all writers. This is
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* needed to guarantee that no writable fds exist to the file once it
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* has verity enabled, and to stabilize the data being hashed.
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*/
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err = file_permission(filp, MAY_WRITE);
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if (err)
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return err;
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if (IS_APPEND(inode))
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return -EPERM;
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if (S_ISDIR(inode->i_mode))
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return -EISDIR;
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if (!S_ISREG(inode->i_mode))
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return -EINVAL;
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err = mnt_want_write_file(filp);
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if (err) /* -EROFS */
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return err;
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err = deny_write_access(filp);
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if (err) /* -ETXTBSY */
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goto out_drop_write;
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err = enable_verity(filp, &arg);
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if (err)
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goto out_allow_write_access;
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/*
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* Some pages of the file may have been evicted from pagecache after
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* being used in the Merkle tree construction, then read into pagecache
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* again by another process reading from the file concurrently. Since
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* these pages didn't undergo verification against the file digest which
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* fs-verity now claims to be enforcing, we have to wipe the pagecache
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* to ensure that all future reads are verified.
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*/
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filemap_write_and_wait(inode->i_mapping);
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invalidate_inode_pages2(inode->i_mapping);
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/*
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* allow_write_access() is needed to pair with deny_write_access().
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* Regardless, the filesystem won't allow writing to verity files.
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*/
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out_allow_write_access:
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allow_write_access(filp);
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out_drop_write:
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mnt_drop_write_file(filp);
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return err;
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}
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EXPORT_SYMBOL_GPL(fsverity_ioctl_enable);
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