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.
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
---
fs/verity/Makefile | 3 +-
fs/verity/enable.c | 339 +++++++++++++++++++++++++++++++++++++++
include/linux/fsverity.h | 64 ++++++++
3 files changed, 405 insertions(+), 1 deletion(-)
create mode 100644 fs/verity/enable.c
diff --git a/fs/verity/Makefile b/fs/verity/Makefile
index 7fa628cd5eba..04b37475fd28 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 000000000000..7e7ef9d3c376
--- /dev/null
+++ b/fs/verity/enable.c
@@ -0,0 +1,339 @@
+// 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;
+
+ 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 = (params->data_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 {
+ /* Successfully enabled verity */
+
+ WARN_ON(!IS_VERITY(inode));
+
+ /*
+ * 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;
+ }
+
+ if (inode->i_size <= 0) {
+ err = -EINVAL;
+ 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 ecd47e748c7f..7ef2ef826534 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)
--
2.21.0
