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Commit 1a932ef4 authored by Liu Bo's avatar Liu Bo Committed by David Sterba
Browse files

Btrfs: fix use-after-free on root->orphan_block_rsv 



I got these from running generic/475,

WARNING: CPU: 0 PID: 26384 at fs/btrfs/inode.c:3326 btrfs_orphan_commit_root+0x1ac/0x2b0 [btrfs]
BUG: unable to handle kernel NULL pointer dereference at 0000000000000010
IP: btrfs_block_rsv_release+0x1c/0x70 [btrfs]
Call Trace:
  btrfs_orphan_release_metadata+0x9f/0x200 [btrfs]
  btrfs_orphan_del+0x10d/0x170 [btrfs]
  btrfs_setattr+0x500/0x640 [btrfs]
  notify_change+0x7ae/0x870
  do_truncate+0xca/0x130
  vfs_truncate+0x2ee/0x3d0
  do_sys_truncate+0xaf/0xf0
  SyS_truncate+0xe/0x10
  entry_SYSCALL_64_fastpath+0x1f/0x96

The race is between btrfs_orphan_commit_root and btrfs_orphan_del,
        t1                                        t2
btrfs_orphan_commit_root                     btrfs_orphan_del
   spin_lock
   check (&root->orphan_inodes)
   root->orphan_block_rsv = NULL;
   spin_unlock
                                             atomic_dec(&root->orphan_inodes);
                                             access root->orphan_block_rsv

Accessing root->orphan_block_rsv must be done before decreasing
root->orphan_inodes.

cc: <stable@vger.kernel.org> v3.12+
Fixes: 703c88e0 ("Btrfs: fix tracking of orphan inode count")
Signed-off-by: default avatarLiu Bo <bo.li.liu@oracle.com>
Reviewed-by: default avatarJosef Bacik <jbacik@fb.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent e8f1bc14

fs/btrfs/inode.c

+21 −13
Original line number Diff line number Diff line
@@ -3387,6 +3387,11 @@ int btrfs_orphan_add(struct btrfs_trans_handle *trans, 
		ret = btrfs_orphan_reserve_metadata(trans, inode);

		ASSERT(!ret);

		if (ret) {

			/*

			 * dec doesn't need spin_lock as ->orphan_block_rsv

			 * would be released only if ->orphan_inodes is

			 * zero.

			 */

			atomic_dec(&root->orphan_inodes);

			clear_bit(BTRFS_INODE_ORPHAN_META_RESERVED,

				  &inode->runtime_flags);
@@ -3401,12 +3406,17 @@ int btrfs_orphan_add(struct btrfs_trans_handle *trans, 
	if (insert >= 1) {

		ret = btrfs_insert_orphan_item(trans, root, btrfs_ino(inode));

		if (ret) {

			atomic_dec(&root->orphan_inodes);

			if (reserve) {

				clear_bit(BTRFS_INODE_ORPHAN_META_RESERVED,

					  &inode->runtime_flags);

				btrfs_orphan_release_metadata(inode);

			}

			/*

			 * btrfs_orphan_commit_root may race with us and set

			 * ->orphan_block_rsv to zero, in order to avoid that,

			 * decrease ->orphan_inodes after everything is done.

			 */

			atomic_dec(&root->orphan_inodes);

			if (ret != -EEXIST) {

				clear_bit(BTRFS_INODE_HAS_ORPHAN_ITEM,

					  &inode->runtime_flags);
@@ -3438,28 +3448,26 @@ static int btrfs_orphan_del(struct btrfs_trans_handle *trans, 
{

	struct btrfs_root *root = inode->root;

	int delete_item = 0;

	int release_rsv = 0;

	int ret = 0;



	spin_lock(&root->orphan_lock);

	if (test_and_clear_bit(BTRFS_INODE_HAS_ORPHAN_ITEM,

			       &inode->runtime_flags))

		delete_item = 1;



	if (delete_item && trans)

		ret = btrfs_del_orphan_item(trans, root, btrfs_ino(inode));



	if (test_and_clear_bit(BTRFS_INODE_ORPHAN_META_RESERVED,

			       &inode->runtime_flags))

		release_rsv = 1;

	spin_unlock(&root->orphan_lock);

		btrfs_orphan_release_metadata(inode);



	if (delete_item) {

	/*

	 * btrfs_orphan_commit_root may race with us and set ->orphan_block_rsv

	 * to zero, in order to avoid that, decrease ->orphan_inodes after

	 * everything is done.

	 */

	if (delete_item)

		atomic_dec(&root->orphan_inodes);

		if (trans)

			ret = btrfs_del_orphan_item(trans, root,

						    btrfs_ino(inode));

	}



	if (release_rsv)

		btrfs_orphan_release_metadata(inode);



	return ret;

}