fs-verity: implement FS_IOC_ENABLE_VERITY ioctl

Add a function for filesystems to call to implement the
FS_IOC_ENABLE_VERITY ioctl.  This ioctl enables fs-verity on a file.

See the "FS_IOC_ENABLE_VERITY" section of
Documentation/filesystems/fsverity.rst for the documentation.

Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
This commit is contained in:
Eric Biggers 2019-07-22 09:26:22 -07:00
parent 8a1d0f9cac
commit 3fda4c617e
3 changed files with 431 additions and 1 deletions

View File

@ -1,6 +1,7 @@
# SPDX-License-Identifier: GPL-2.0
obj-$(CONFIG_FS_VERITY) += hash_algs.o \
obj-$(CONFIG_FS_VERITY) += enable.o \
hash_algs.o \
init.o \
open.o \
verify.o

363
fs/verity/enable.c Normal file
View File

@ -0,0 +1,363 @@
// SPDX-License-Identifier: GPL-2.0
/*
* fs/verity/enable.c: ioctl to enable verity on a file
*
* Copyright 2019 Google LLC
*/
#include "fsverity_private.h"
#include <crypto/hash.h>
#include <linux/mount.h>
#include <linux/pagemap.h>
#include <linux/sched/signal.h>
#include <linux/uaccess.h>
static int build_merkle_tree_level(struct inode *inode, unsigned int level,
u64 num_blocks_to_hash,
const struct merkle_tree_params *params,
u8 *pending_hashes,
struct ahash_request *req)
{
const struct fsverity_operations *vops = inode->i_sb->s_vop;
unsigned int pending_size = 0;
u64 dst_block_num;
u64 i;
int err;
if (WARN_ON(params->block_size != PAGE_SIZE)) /* checked earlier too */
return -EINVAL;
if (level < params->num_levels) {
dst_block_num = params->level_start[level];
} else {
if (WARN_ON(num_blocks_to_hash != 1))
return -EINVAL;
dst_block_num = 0; /* unused */
}
for (i = 0; i < num_blocks_to_hash; i++) {
struct page *src_page;
if ((pgoff_t)i % 10000 == 0 || i + 1 == num_blocks_to_hash)
pr_debug("Hashing block %llu of %llu for level %u\n",
i + 1, num_blocks_to_hash, level);
if (level == 0) {
/* Leaf: hashing a data block */
src_page = read_mapping_page(inode->i_mapping, i, NULL);
if (IS_ERR(src_page)) {
err = PTR_ERR(src_page);
fsverity_err(inode,
"Error %d reading data page %llu",
err, i);
return err;
}
} else {
/* Non-leaf: hashing hash block from level below */
src_page = vops->read_merkle_tree_page(inode,
params->level_start[level - 1] + i);
if (IS_ERR(src_page)) {
err = PTR_ERR(src_page);
fsverity_err(inode,
"Error %d reading Merkle tree page %llu",
err, params->level_start[level - 1] + i);
return err;
}
}
err = fsverity_hash_page(params, inode, req, src_page,
&pending_hashes[pending_size]);
put_page(src_page);
if (err)
return err;
pending_size += params->digest_size;
if (level == params->num_levels) /* Root hash? */
return 0;
if (pending_size + params->digest_size > params->block_size ||
i + 1 == num_blocks_to_hash) {
/* Flush the pending hash block */
memset(&pending_hashes[pending_size], 0,
params->block_size - pending_size);
err = vops->write_merkle_tree_block(inode,
pending_hashes,
dst_block_num,
params->log_blocksize);
if (err) {
fsverity_err(inode,
"Error %d writing Merkle tree block %llu",
err, dst_block_num);
return err;
}
dst_block_num++;
pending_size = 0;
}
if (fatal_signal_pending(current))
return -EINTR;
cond_resched();
}
return 0;
}
/*
* Build the Merkle tree for the given inode using the given parameters, and
* return the root hash in @root_hash.
*
* The tree is written to a filesystem-specific location as determined by the
* ->write_merkle_tree_block() method. However, the blocks that comprise the
* tree are the same for all filesystems.
*/
static int build_merkle_tree(struct inode *inode,
const struct merkle_tree_params *params,
u8 *root_hash)
{
u8 *pending_hashes;
struct ahash_request *req;
u64 blocks;
unsigned int level;
int err = -ENOMEM;
if (inode->i_size == 0) {
/* Empty file is a special case; root hash is all 0's */
memset(root_hash, 0, params->digest_size);
return 0;
}
pending_hashes = kmalloc(params->block_size, GFP_KERNEL);
req = ahash_request_alloc(params->hash_alg->tfm, GFP_KERNEL);
if (!pending_hashes || !req)
goto out;
/*
* Build each level of the Merkle tree, starting at the leaf level
* (level 0) and ascending to the root node (level 'num_levels - 1').
* Then at the end (level 'num_levels'), calculate the root hash.
*/
blocks = (inode->i_size + params->block_size - 1) >>
params->log_blocksize;
for (level = 0; level <= params->num_levels; level++) {
err = build_merkle_tree_level(inode, level, blocks, params,
pending_hashes, req);
if (err)
goto out;
blocks = (blocks + params->hashes_per_block - 1) >>
params->log_arity;
}
memcpy(root_hash, pending_hashes, params->digest_size);
err = 0;
out:
kfree(pending_hashes);
ahash_request_free(req);
return err;
}
static int enable_verity(struct file *filp,
const struct fsverity_enable_arg *arg)
{
struct inode *inode = file_inode(filp);
const struct fsverity_operations *vops = inode->i_sb->s_vop;
struct merkle_tree_params params = { };
struct fsverity_descriptor *desc;
size_t desc_size = sizeof(*desc);
struct fsverity_info *vi;
int err;
/* Start initializing the fsverity_descriptor */
desc = kzalloc(desc_size, GFP_KERNEL);
if (!desc)
return -ENOMEM;
desc->version = 1;
desc->hash_algorithm = arg->hash_algorithm;
desc->log_blocksize = ilog2(arg->block_size);
/* Get the salt if the user provided one */
if (arg->salt_size &&
copy_from_user(desc->salt,
(const u8 __user *)(uintptr_t)arg->salt_ptr,
arg->salt_size)) {
err = -EFAULT;
goto out;
}
desc->salt_size = arg->salt_size;
desc->data_size = cpu_to_le64(inode->i_size);
/* Prepare the Merkle tree parameters */
err = fsverity_init_merkle_tree_params(&params, inode,
arg->hash_algorithm,
desc->log_blocksize,
desc->salt, desc->salt_size);
if (err)
goto out;
/*
* Start enabling verity on this file, serialized by the inode lock.
* Fail if verity is already enabled or is already being enabled.
*/
inode_lock(inode);
if (IS_VERITY(inode))
err = -EEXIST;
else
err = vops->begin_enable_verity(filp);
inode_unlock(inode);
if (err)
goto out;
/*
* Build the Merkle tree. Don't hold the inode lock during this, since
* on huge files this may take a very long time and we don't want to
* force unrelated syscalls like chown() to block forever. We don't
* need the inode lock here because deny_write_access() already prevents
* the file from being written to or truncated, and we still serialize
* ->begin_enable_verity() and ->end_enable_verity() using the inode
* lock and only allow one process to be here at a time on a given file.
*/
pr_debug("Building Merkle tree...\n");
BUILD_BUG_ON(sizeof(desc->root_hash) < FS_VERITY_MAX_DIGEST_SIZE);
err = build_merkle_tree(inode, &params, desc->root_hash);
if (err) {
fsverity_err(inode, "Error %d building Merkle tree", err);
goto rollback;
}
pr_debug("Done building Merkle tree. Root hash is %s:%*phN\n",
params.hash_alg->name, params.digest_size, desc->root_hash);
/*
* Create the fsverity_info. Don't bother trying to save work by
* reusing the merkle_tree_params from above. Instead, just create the
* fsverity_info from the fsverity_descriptor as if it were just loaded
* from disk. This is simpler, and it serves as an extra check that the
* metadata we're writing is valid before actually enabling verity.
*/
vi = fsverity_create_info(inode, desc, desc_size);
if (IS_ERR(vi)) {
err = PTR_ERR(vi);
goto rollback;
}
/*
* Tell the filesystem to finish enabling verity on the file.
* Serialized with ->begin_enable_verity() by the inode lock.
*/
inode_lock(inode);
err = vops->end_enable_verity(filp, desc, desc_size, params.tree_size);
inode_unlock(inode);
if (err) {
fsverity_err(inode, "%ps() failed with err %d",
vops->end_enable_verity, err);
fsverity_free_info(vi);
} else if (WARN_ON(!IS_VERITY(inode))) {
err = -EINVAL;
fsverity_free_info(vi);
} else {
/* Successfully enabled verity */
/*
* Readers can start using ->i_verity_info immediately, so it
* can't be rolled back once set. So don't set it until just
* after the filesystem has successfully enabled verity.
*/
fsverity_set_info(inode, vi);
}
out:
kfree(params.hashstate);
kfree(desc);
return err;
rollback:
inode_lock(inode);
(void)vops->end_enable_verity(filp, NULL, 0, params.tree_size);
inode_unlock(inode);
goto out;
}
/**
* fsverity_ioctl_enable() - enable verity on a file
*
* Enable fs-verity on a file. See the "FS_IOC_ENABLE_VERITY" section of
* Documentation/filesystems/fsverity.rst for the documentation.
*
* Return: 0 on success, -errno on failure
*/
int fsverity_ioctl_enable(struct file *filp, const void __user *uarg)
{
struct inode *inode = file_inode(filp);
struct fsverity_enable_arg arg;
int err;
if (copy_from_user(&arg, uarg, sizeof(arg)))
return -EFAULT;
if (arg.version != 1)
return -EINVAL;
if (arg.__reserved1 ||
memchr_inv(arg.__reserved2, 0, sizeof(arg.__reserved2)))
return -EINVAL;
if (arg.block_size != PAGE_SIZE)
return -EINVAL;
if (arg.salt_size > FIELD_SIZEOF(struct fsverity_descriptor, salt))
return -EMSGSIZE;
if (arg.sig_size)
return -EINVAL;
/*
* Require a regular file with write access. But the actual fd must
* still be readonly so that we can lock out all writers. This is
* needed to guarantee that no writable fds exist to the file once it
* has verity enabled, and to stabilize the data being hashed.
*/
err = inode_permission(inode, MAY_WRITE);
if (err)
return err;
if (IS_APPEND(inode))
return -EPERM;
if (S_ISDIR(inode->i_mode))
return -EISDIR;
if (!S_ISREG(inode->i_mode))
return -EINVAL;
err = mnt_want_write_file(filp);
if (err) /* -EROFS */
return err;
err = deny_write_access(filp);
if (err) /* -ETXTBSY */
goto out_drop_write;
err = enable_verity(filp, &arg);
if (err)
goto out_allow_write_access;
/*
* Some pages of the file may have been evicted from pagecache after
* being used in the Merkle tree construction, then read into pagecache
* again by another process reading from the file concurrently. Since
* these pages didn't undergo verification against the file measurement
* which fs-verity now claims to be enforcing, we have to wipe the
* pagecache to ensure that all future reads are verified.
*/
filemap_write_and_wait(inode->i_mapping);
invalidate_inode_pages2(inode->i_mapping);
/*
* allow_write_access() is needed to pair with deny_write_access().
* Regardless, the filesystem won't allow writing to verity files.
*/
out_allow_write_access:
allow_write_access(filp);
out_drop_write:
mnt_drop_write_file(filp);
return err;
}
EXPORT_SYMBOL_GPL(fsverity_ioctl_enable);

View File

@ -17,6 +17,44 @@
/* Verity operations for filesystems */
struct fsverity_operations {
/**
* Begin enabling verity on the given file.
*
* @filp: a readonly file descriptor for the file
*
* The filesystem must do any needed filesystem-specific preparations
* for enabling verity, e.g. evicting inline data. It also must return
* -EBUSY if verity is already being enabled on the given file.
*
* i_rwsem is held for write.
*
* Return: 0 on success, -errno on failure
*/
int (*begin_enable_verity)(struct file *filp);
/**
* End enabling verity on the given file.
*
* @filp: a readonly file descriptor for the file
* @desc: the verity descriptor to write, or NULL on failure
* @desc_size: size of verity descriptor, or 0 on failure
* @merkle_tree_size: total bytes the Merkle tree took up
*
* If desc == NULL, then enabling verity failed and the filesystem only
* must do any necessary cleanups. Else, it must also store the given
* verity descriptor to a fs-specific location associated with the inode
* and do any fs-specific actions needed to mark the inode as a verity
* inode, e.g. setting a bit in the on-disk inode. The filesystem is
* also responsible for setting the S_VERITY flag in the VFS inode.
*
* i_rwsem is held for write, but it may have been dropped between
* ->begin_enable_verity() and ->end_enable_verity().
*
* Return: 0 on success, -errno on failure
*/
int (*end_enable_verity)(struct file *filp, const void *desc,
size_t desc_size, u64 merkle_tree_size);
/**
* Get the verity descriptor of the given inode.
*
@ -50,6 +88,22 @@ struct fsverity_operations {
*/
struct page *(*read_merkle_tree_page)(struct inode *inode,
pgoff_t index);
/**
* Write a Merkle tree block to the given inode.
*
* @inode: the inode for which the Merkle tree is being built
* @buf: block to write
* @index: 0-based index of the block within the Merkle tree
* @log_blocksize: log base 2 of the Merkle tree block size
*
* This is only called between ->begin_enable_verity() and
* ->end_enable_verity().
*
* Return: 0 on success, -errno on failure
*/
int (*write_merkle_tree_block)(struct inode *inode, const void *buf,
u64 index, int log_blocksize);
};
#ifdef CONFIG_FS_VERITY
@ -60,6 +114,10 @@ static inline struct fsverity_info *fsverity_get_info(const struct inode *inode)
return READ_ONCE(inode->i_verity_info);
}
/* enable.c */
extern int fsverity_ioctl_enable(struct file *filp, const void __user *arg);
/* open.c */
extern int fsverity_file_open(struct inode *inode, struct file *filp);
@ -79,6 +137,14 @@ static inline struct fsverity_info *fsverity_get_info(const struct inode *inode)
return NULL;
}
/* enable.c */
static inline int fsverity_ioctl_enable(struct file *filp,
const void __user *arg)
{
return -EOPNOTSUPP;
}
/* open.c */
static inline int fsverity_file_open(struct inode *inode, struct file *filp)