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-rw-r--r--fs/verity/enable.c405
1 files changed, 405 insertions, 0 deletions
diff --git a/fs/verity/enable.c b/fs/verity/enable.c
new file mode 100644
index 0000000000..c284f46d1b
--- /dev/null
+++ b/fs/verity/enable.c
@@ -0,0 +1,405 @@
+// 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/mount.h>
+#include <linux/sched/signal.h>
+#include <linux/uaccess.h>
+
+struct block_buffer {
+ u32 filled;
+ bool is_root_hash;
+ u8 *data;
+};
+
+/* Hash a block, writing the result to the next level's pending block buffer. */
+static int hash_one_block(struct inode *inode,
+ const struct merkle_tree_params *params,
+ struct block_buffer *cur)
+{
+ struct block_buffer *next = cur + 1;
+ int err;
+
+ /*
+ * Safety check to prevent a buffer overflow in case of a filesystem bug
+ * that allows the file size to change despite deny_write_access(), or a
+ * bug in the Merkle tree logic itself
+ */
+ if (WARN_ON_ONCE(next->is_root_hash && next->filled != 0))
+ return -EINVAL;
+
+ /* Zero-pad the block if it's shorter than the block size. */
+ memset(&cur->data[cur->filled], 0, params->block_size - cur->filled);
+
+ err = fsverity_hash_block(params, inode, cur->data,
+ &next->data[next->filled]);
+ if (err)
+ return err;
+ next->filled += params->digest_size;
+ cur->filled = 0;
+ return 0;
+}
+
+static int write_merkle_tree_block(struct inode *inode, const u8 *buf,
+ unsigned long index,
+ const struct merkle_tree_params *params)
+{
+ u64 pos = (u64)index << params->log_blocksize;
+ int err;
+
+ err = inode->i_sb->s_vop->write_merkle_tree_block(inode, buf, pos,
+ params->block_size);
+ if (err)
+ fsverity_err(inode, "Error %d writing Merkle tree block %lu",
+ err, index);
+ return err;
+}
+
+/*
+ * 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);
+ const u64 data_size = inode->i_size;
+ const int num_levels = params->num_levels;
+ struct block_buffer _buffers[1 + FS_VERITY_MAX_LEVELS + 1] = {};
+ struct block_buffer *buffers = &_buffers[1];
+ unsigned long level_offset[FS_VERITY_MAX_LEVELS];
+ int level;
+ u64 offset;
+ int err;
+
+ if (data_size == 0) {
+ /* Empty file is a special case; root hash is all 0's */
+ memset(root_hash, 0, params->digest_size);
+ return 0;
+ }
+
+ /*
+ * Allocate the block buffers. Buffer "-1" is for data blocks.
+ * Buffers 0 <= level < num_levels are for the actual tree levels.
+ * Buffer 'num_levels' is for the root hash.
+ */
+ for (level = -1; level < num_levels; level++) {
+ buffers[level].data = kzalloc(params->block_size, GFP_KERNEL);
+ if (!buffers[level].data) {
+ err = -ENOMEM;
+ goto out;
+ }
+ }
+ buffers[num_levels].data = root_hash;
+ buffers[num_levels].is_root_hash = true;
+
+ BUILD_BUG_ON(sizeof(level_offset) != sizeof(params->level_start));
+ memcpy(level_offset, params->level_start, sizeof(level_offset));
+
+ /* Hash each data block, also hashing the tree blocks as they fill up */
+ for (offset = 0; offset < data_size; offset += params->block_size) {
+ ssize_t bytes_read;
+ loff_t pos = offset;
+
+ buffers[-1].filled = min_t(u64, params->block_size,
+ data_size - offset);
+ bytes_read = __kernel_read(filp, buffers[-1].data,
+ buffers[-1].filled, &pos);
+ if (bytes_read < 0) {
+ err = bytes_read;
+ fsverity_err(inode, "Error %d reading file data", err);
+ goto out;
+ }
+ if (bytes_read != buffers[-1].filled) {
+ err = -EINVAL;
+ fsverity_err(inode, "Short read of file data");
+ goto out;
+ }
+ err = hash_one_block(inode, params, &buffers[-1]);
+ if (err)
+ goto out;
+ for (level = 0; level < num_levels; level++) {
+ if (buffers[level].filled + params->digest_size <=
+ params->block_size) {
+ /* Next block at @level isn't full yet */
+ break;
+ }
+ /* Next block at @level is full */
+
+ err = hash_one_block(inode, params, &buffers[level]);
+ if (err)
+ goto out;
+ err = write_merkle_tree_block(inode,
+ buffers[level].data,
+ level_offset[level],
+ params);
+ if (err)
+ goto out;
+ level_offset[level]++;
+ }
+ if (fatal_signal_pending(current)) {
+ err = -EINTR;
+ goto out;
+ }
+ cond_resched();
+ }
+ /* Finish all nonempty pending tree blocks. */
+ for (level = 0; level < num_levels; level++) {
+ if (buffers[level].filled != 0) {
+ err = hash_one_block(inode, params, &buffers[level]);
+ if (err)
+ goto out;
+ err = write_merkle_tree_block(inode,
+ buffers[level].data,
+ level_offset[level],
+ params);
+ if (err)
+ goto out;
+ }
+ }
+ /* The root hash was filled by the last call to hash_one_block(). */
+ if (WARN_ON_ONCE(buffers[num_levels].filled != params->digest_size)) {
+ err = -EINVAL;
+ goto out;
+ }
+ err = 0;
+out:
+ for (level = -1; level < num_levels; level++)
+ kfree(buffers[level].data);
+ 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 = struct_size(desc, signature, 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 builtin 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.
+ */
+ 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;
+ }
+
+ /*
+ * 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);
+ 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_ONCE(!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 (!is_power_of_2(arg.block_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;
+ /*
+ * __kernel_read() is used while building the Merkle tree. So, we can't
+ * allow file descriptors that were opened for ioctl access only, using
+ * the special nonstandard access mode 3. O_RDONLY only, please!
+ */
+ if (!(filp->f_mode & FMODE_READ))
+ return -EBADF;
+
+ 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);
+
+ /*
+ * We no longer drop the inode's pagecache after enabling verity. This
+ * used to be done to try to avoid a race condition where pages could be
+ * evicted after being used in the Merkle tree construction, then
+ * re-instantiated by a concurrent read. Such pages are unverified, and
+ * the backing storage could have filled them with different content, so
+ * they shouldn't be used to fulfill reads once verity is enabled.
+ *
+ * But, dropping the pagecache has a big performance impact, and it
+ * doesn't fully solve the race condition anyway. So for those reasons,
+ * and also because this race condition isn't very important relatively
+ * speaking (especially for small-ish files, where the chance of a page
+ * being used, evicted, *and* re-instantiated all while enabling verity
+ * is quite small), we no longer drop the inode's pagecache.
+ */
+
+ /*
+ * allow_write_access() is needed to pair with deny_write_access().
+ * Regardless, the filesystem won't allow writing to verity files.
+ */
+ allow_write_access(filp);
+out_drop_write:
+ mnt_drop_write_file(filp);
+ return err;
+}
+EXPORT_SYMBOL_GPL(fsverity_ioctl_enable);
generated by cgit v1.2.3 (git 2.39.1) at 2024-09-23 21:25:11 +0000