Date:   Sat, 22 Jun 2019 15:43:19 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     linux-fscrypt@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org,
        linux-integrity@...r.kernel.org,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Victor Hsieh <victorhsieh@...gle.com>,
        Chandan Rajendra <chandan@...ux.vnet.ibm.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v5 10/16] fs-verity: implement FS_IOC_ENABLE_VERITY ioctl

On 06/20, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@...gle.com>
> 
> 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@...nel.org>

> Signed-off-by: Eric Biggers <ebiggers@...gle.com>
> ---
>  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(&params, 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, &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 */
> +	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

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