fs/verity/enable.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Ioctl to enable verity on a file
  *
  * Copyright 2019 Google LLC
  */

 #include "fsverity_private.h"

 #include <crypto/hash.h>
 #include <linux/backing-dev.h>
 #include <linux/mount.h>
 #include <linux/pagemap.h>
 #include <linux/sched/signal.h>
 #include <linux/uaccess.h>

 /*
  * Read a file data page for Merkle tree construction.  Do aggressive readahead,
  * since we're sequentially reading the entire file.
  */
 static struct page *read_file_data_page(struct file *filp, pgoff_t index,
 					struct file_ra_state *ra,
 					unsigned long remaining_pages)
 {
 	struct page *page;

 	page = find_get_page_flags(filp->f_mapping, index, FGP_ACCESSED);
 	if (!page || !PageUptodate(page)) {
 		if (page)
 			put_page(page);
 		else
 			page_cache_sync_readahead(filp->f_mapping, ra, filp,
 						  index, remaining_pages);
 		page = read_mapping_page(filp->f_mapping, index, NULL);
 		if (IS_ERR(page))
 			return page;
 	}
 	if (PageReadahead(page))
 		page_cache_async_readahead(filp->f_mapping, ra, filp, page,
 					   index, remaining_pages);
 	return page;
 }

 static int build_merkle_tree_level(struct file *filp, unsigned int level,
 				   u64 num_blocks_to_hash,
 				   const struct merkle_tree_params *params,
 				   u8 *pending_hashes,
 				   struct ahash_request *req)
 {
 	struct inode *inode = file_inode(filp);
 	const struct fsverity_operations *vops = inode->i_sb->s_vop;
 	struct file_ra_state ra = { 0 };
 	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 */
 	}

 	file_ra_state_init(&ra, filp->f_mapping);

 	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_file_data_page(filp, i, &ra,
 						       num_blocks_to_hash - i);
 			if (IS_ERR(src_page)) {
 				err = PTR_ERR(src_page);
 				fsverity_err(inode,
 					     "Error %d reading data page %llu",
 					     err, i);
 				return err;
 			}
 		} else {
 			unsigned long num_ra_pages =
 				min_t(unsigned long, num_blocks_to_hash - i,
 				      inode->i_sb->s_bdi->io_pages);

 			/* Non-leaf: hashing hash block from level below */
 			src_page = vops->read_merkle_tree_page(inode,
 					params->level_start[level - 1] + i,
 					num_ra_pages);
 			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 file 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 file *filp,
 			     const struct merkle_tree_params *params,
 			     u8 *root_hash)
 {
 	struct inode *inode = file_inode(filp);
 	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;
 	}

 	/* This allocation never fails, since it's mempool-backed. */
 	req = fsverity_alloc_hash_request(params->hash_alg, GFP_KERNEL);

 	pending_hashes = kmalloc(params->block_size, GFP_KERNEL);
 	if (!pending_hashes)
 		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(filp, 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);
 	fsverity_free_hash_request(params->hash_alg, 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) + arg->sig_size;
 	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, u64_to_user_ptr(arg->salt_ptr),
 			   arg->salt_size)) {
 		err = -EFAULT;
 		goto out;
 	}
 	desc->salt_size = arg->salt_size;

 	/* Get the signature if the user provided one */
 	if (arg->sig_size &&
 	    copy_from_user(desc->signature, u64_to_user_ptr(arg->sig_ptr),
 			   arg->sig_size)) {
 		err = -EFAULT;
 		goto out;
 	}
 	desc->sig_size = cpu_to_le32(arg->sig_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(filp, &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;
 	}

 	if (arg->sig_size)
 		pr_debug("Storing a %u-byte PKCS#7 signature alongside the file\n",
 			 arg->sig_size);

 	/*
 	 * 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
  * @filp: file to enable verity on
  * @uarg: user pointer to fsverity_enable_arg
  *
  * 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 > sizeof_field(struct fsverity_descriptor, salt))
 		return -EMSGSIZE;

 	if (arg.sig_size > FS_VERITY_MAX_SIGNATURE_SIZE)
 		return -EMSGSIZE;

 	/*
 	 * 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 = file_permission(filp, 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 digest 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);
	// SPDX-License-Identifier: GPL-2.0
	/*
	* Ioctl to enable verity on a file
	*
	* Copyright 2019 Google LLC
	*/

	#include "fsverity_private.h"

	#include <crypto/hash.h>
	#include <linux/backing-dev.h>
	#include <linux/mount.h>
	#include <linux/pagemap.h>
	#include <linux/sched/signal.h>
	#include <linux/uaccess.h>

	/*
	* Read a file data page for Merkle tree construction. Do aggressive readahead,
	* since we're sequentially reading the entire file.
	*/
	static struct page read_file_data_page(struct file filp, pgoff_t index,
	struct file_ra_state *ra,
	unsigned long remaining_pages)
	{
	struct page *page;

	page = find_get_page_flags(filp->f_mapping, index, FGP_ACCESSED);
	if (!page \|\| !PageUptodate(page)) {
	if (page)
	put_page(page);
	else
	page_cache_sync_readahead(filp->f_mapping, ra, filp,
	index, remaining_pages);
	page = read_mapping_page(filp->f_mapping, index, NULL);
	if (IS_ERR(page))
	return page;
	}
	if (PageReadahead(page))
	page_cache_async_readahead(filp->f_mapping, ra, filp, page,
	index, remaining_pages);
	return page;
	}

	static int build_merkle_tree_level(struct file *filp, unsigned int level,
	u64 num_blocks_to_hash,
	const struct merkle_tree_params *params,
	u8 *pending_hashes,
	struct ahash_request *req)
	{
	struct inode *inode = file_inode(filp);
	const struct fsverity_operations *vops = inode->i_sb->s_vop;
	struct file_ra_state ra = { 0 };
	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 */
	}

	file_ra_state_init(&ra, filp->f_mapping);

	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_file_data_page(filp, i, &ra,
	num_blocks_to_hash - i);
	if (IS_ERR(src_page)) {
	err = PTR_ERR(src_page);
	fsverity_err(inode,
	"Error %d reading data page %llu",
	err, i);
	return err;
	}
	} else {
	unsigned long num_ra_pages =
	min_t(unsigned long, num_blocks_to_hash - i,
	inode->i_sb->s_bdi->io_pages);

	/* Non-leaf: hashing hash block from level below */
	src_page = vops->read_merkle_tree_page(inode,
	params->level_start[level - 1] + i,
	num_ra_pages);
	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 file 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 file *filp,
	const struct merkle_tree_params *params,
	u8 *root_hash)
	{
	struct inode *inode = file_inode(filp);
	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;
	}

	/* This allocation never fails, since it's mempool-backed. */
	req = fsverity_alloc_hash_request(params->hash_alg, GFP_KERNEL);

	pending_hashes = kmalloc(params->block_size, GFP_KERNEL);
	if (!pending_hashes)
	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(filp, 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);
	fsverity_free_hash_request(params->hash_alg, 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) + arg->sig_size;
	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, u64_to_user_ptr(arg->salt_ptr),
	arg->salt_size)) {
	err = -EFAULT;
	goto out;
	}
	desc->salt_size = arg->salt_size;

	/* Get the signature if the user provided one */
	if (arg->sig_size &&
	copy_from_user(desc->signature, u64_to_user_ptr(arg->sig_ptr),
	arg->sig_size)) {
	err = -EFAULT;
	goto out;
	}
	desc->sig_size = cpu_to_le32(arg->sig_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(filp, &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;
	}

	if (arg->sig_size)
	pr_debug("Storing a %u-byte PKCS#7 signature alongside the file\n",
	arg->sig_size);

	/*
	* 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
	* @filp: file to enable verity on
	* @uarg: user pointer to fsverity_enable_arg
	*
	* 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 > sizeof_field(struct fsverity_descriptor, salt))
	return -EMSGSIZE;

	if (arg.sig_size > FS_VERITY_MAX_SIGNATURE_SIZE)
	return -EMSGSIZE;

	/*
	* 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 = file_permission(filp, 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 digest 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);