CVE-2012-5375 (C, published 2013-02-18T11:56Z)
Description: value: The CRC32C feature in the Btrfs implementation in the Linux kernel before 3.8-rc1 allows local users to cause a denial of service (prevention of file creation) by leveraging the ability to write to a directory important to the victim, and creating a file with a crafted name that is associated with a specific CRC32C hash value.
Severity: MEDIUM (CVSS v3 base score: )
Weakness: CWE-310 \u2014 Cryptographic Issues
Weaknesses in this category are related to the design and implementation of data confidentiality and integrity. Frequently these deal with the use of encoding techniques, encryption libraries, and hashing algorithms. The weaknesses in this category could lead to a degradation of the quality data if they are not addressed.
Repository: https://github.com/torvalds/linux
Files changed:
fs/btrfs/ctree.h
fs/btrfs/dir-item.c
fs/btrfs/inode.c
fs/btrfs/ioctl.c
fs/btrfs/transaction.c
Commit message: Btrfs: fix hash overflow handling

The handling for directory crc hash overflows was fairly obscure,
split_leaf returns EOVERFLOW when we try to extend the item and that is
supposed to bubble up to userland.  For a while it did so, but along the
way we added better handling of errors and forced the FS readonly if we
hit IO errors during the directory insertion.

Along the way, we started testing only for EEXIST and the EOVERFLOW case
was dropped.  The end result is that we may force the FS readonly if we
catch a directory hash bucket overflow.

This fixes a few problem spots.  First I add tests for EOVERFLOW in the
places where we can safely just return the error up the chain.

btrfs_rename is harder though, because it tries to insert the new
directory item only after it has already unlinked anything the rename
was going to overwrite.  Rather than adding very complex logic, I added
a helper to test for the hash overflow case early while it is still safe
to bail out.

Snapshot and subvolume creation had a similar problem, so they are using
the new helper now too.

Signed-off-by: Chris Mason <chris.mason@fusionio.com>
Reported-by: Pascal Junod <pascal@junod.info>


Vulnerable code:
	if (ret == -EEXIST)
	BUG_ON(ret == -EEXIST);

Fixed code:
int btrfs_check_dir_item_collision(struct btrfs_root *root, u64 dir,
			  const char *name, int name_len);
int btrfs_check_dir_item_collision(struct btrfs_root *root, u64 dir,
				   const char *name, int name_len)
{
	int ret;
	struct btrfs_key key;
	struct btrfs_dir_item *di;
	int data_size;
	struct extent_buffer *leaf;
	int slot;
	struct btrfs_path *path;


	path = btrfs_alloc_path();
	if (!path)
		return -ENOMEM;

	key.objectid = dir;
	btrfs_set_key_type(&key, BTRFS_DIR_ITEM_KEY);
	key.offset = btrfs_name_hash(name, name_len);

	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);

	/* return back any errors */
	if (ret < 0)
		goto out;

	/* nothing found, we're safe */
	if (ret > 0) {
		ret = 0;
		goto out;
	}

	/* we found an item, look for our name in the item */
	di = btrfs_match_dir_item_name(root, path, name, name_len);
	if (di) {
		/* our exact name was found */
		ret = -EEXIST;
		goto out;
	}

	/*
	 * see if there is room in the item to insert this
	 * name
	 */
	data_size = sizeof(*di) + name_len + sizeof(struct btrfs_item);
	leaf = path->nodes[0];
	slot = path->slots[0];
	if (data_size + btrfs_item_size_nr(leaf, slot) +
	    sizeof(struct btrfs_item) > BTRFS_LEAF_DATA_SIZE(root)) {
		ret = -EOVERFLOW;
	} else {
		/* plenty of insertion room */
		ret = 0;
	}
out:
	btrfs_free_path(path);
	return ret;
}

	if (ret == -EEXIST || ret == -EOVERFLOW)


	/* check for collisions, even if the  name isn't there */
	ret = btrfs_check_dir_item_collision(root, new_dir->i_ino,
			     new_dentry->d_name.name,
			     new_dentry->d_name.len);

	if (ret) {
		if (ret == -EEXIST) {
			/* we shouldn't get
			 * eexist without a new_inode */
			if (!new_inode) {
				WARN_ON(1);
				return ret;
			}
		} else {
			/* maybe -EOVERFLOW */
			return ret;
		}
	}
	ret = 0;

	/*
	 * even if this name doesn't exist, we may get hash collisions.
	 * check for them now when we can safely fail
	 */
	error = btrfs_check_dir_item_collision(BTRFS_I(dir)->root,
					       dir->i_ino, name,
					       namelen);
	if (error)
		goto out_dput;

	BUG_ON(ret == -EEXIST || ret == -EOVERFLOW);