On 06/20, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@xxxxxxxxxx>
>
> 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: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
> ---
> fs/verity/Makefile | 3 +-
> fs/verity/enable.c | 341 +++++++++++++++++++++++++++++++++++++++
> include/linux/fsverity.h | 64 ++++++++
> 3 files changed, 407 insertions(+), 1 deletion(-)
> create mode 100644 fs/verity/enable.c
>
> diff --git a/fs/verity/Makefile b/fs/verity/Makefile
> index 7fa628cd5eba24..04b37475fd280a 100644
> --- a/fs/verity/Makefile
> +++ b/fs/verity/Makefile
> @@ -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
> diff --git a/fs/verity/enable.c b/fs/verity/enable.c
> new file mode 100644
> index 00000000000000..144721bbe4aab9
> --- /dev/null
> +++ b/fs/verity/enable.c
> @@ -0,0 +1,341 @@
> +// 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);
> + 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);
> +
> + pr_debug("Building Merkle tree...\n");
> +
> + /* Prepare the Merkle tree parameters */
> + err = fsverity_init_merkle_tree_params(¶ms, inode,
> + arg->hash_algorithm,
> + desc->log_blocksize,
> + desc->salt, desc->salt_size);
> + if (err)
> + goto out;
> +
> + /* Tell the filesystem that verity is being enabled on the file */
> + err = vops->begin_enable_verity(filp);
> + if (err)
> + goto out;
> +
> + /* Build the Merkle tree */
> + BUILD_BUG_ON(sizeof(desc->root_hash) < FS_VERITY_MAX_DIGEST_SIZE);
> + err = build_merkle_tree(inode, ¶ms, 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 */
> + err = vops->end_enable_verity(filp, desc, desc_size, params.tree_size);
> + 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:
> + (void)vops->end_enable_verity(filp, NULL, 0, params.tree_size);
> + 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;
> +
> + inode_lock(inode);
> +
> + if (IS_VERITY(inode)) {
> + err = -EEXIST;
> + goto out_unlock;
> + }
> +
> + err = enable_verity(filp, &arg);
> + if (err)
> + goto out_unlock;
> +
> + /*
> + * 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);
> + truncate_inode_pages(inode->i_mapping, 0);
> +
> + /*
> + * allow_write_access() is needed to pair with deny_write_access().
> + * Regardless, the filesystem won't allow writing to verity files.
> + */
> +out_unlock:
> + inode_unlock(inode);
> + allow_write_access(filp);
> +out_drop_write:
> + mnt_drop_write_file(filp);
> + return err;
> +}
> +EXPORT_SYMBOL_GPL(fsverity_ioctl_enable);
> diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h
> index ecd47e748c7f64..7ef2ef82653409 100644
> --- a/include/linux/fsverity.h
> +++ b/include/linux/fsverity.h
> @@ -17,6 +17,42 @@
> /* 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.
> + *
> + * 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.
> + *
> + * 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 +86,22 @@ 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(). i_rwsem is held for write.
> + *
> + * 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 +112,10 @@ 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 +135,14 @@ 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)
> --
> 2.22.0.410.gd8fdbe21b5-goog
