Merge tag 'make-attr-fork-permanent-5.20_2022-07-14' of git://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux into xfs-5.20-mergeB

xfs: make attr forks permanent

This series fixes a use-after-free bug that syzbot uncovered.  The UAF
itself is a result of a race condition between getxattr and removexattr
because callers to getxattr do not necessarily take any sort of locks
before calling into the filesystem.

Although the race condition itself can be fixed through clever use of a
memory barrier, further consideration of the use cases of extended
attributes shows that most files always have at least one attribute, so
we might as well make them permanent.

v2: Minor tweaks suggested by Dave, and convert some more macros to
helper functions.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>

* tag 'make-attr-fork-permanent-5.20_2022-07-14' of git://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux:
  xfs: replace inode fork size macros with functions
  xfs: replace XFS_IFORK_Q with a proper predicate function
  xfs: use XFS_IFORK_Q to determine the presence of an xattr fork
  xfs: make inode attribute forks a permanent part of struct xfs_inode
  xfs: convert XFS_IFORK_PTR to a static inline helper

1 files changed, 6 insertions, 10 deletions

diff --git a/fs/xfs/xfs_attr_inactive.c b/fs/xfs/xfs_attr_inactive.c
index 27265771f247..0e83cab9cdde 100644
--- a/fs/xfs/xfs_attr_inactive.c
+++ b/fs/xfs/xfs_attr_inactive.c
@@ -338,7 +338,7 @@ xfs_attr_inactive(
 	ASSERT(! XFS_NOT_DQATTACHED(mp, dp));
 
 	xfs_ilock(dp, lock_mode);
-	if (!XFS_IFORK_Q(dp))
+	if (!xfs_inode_has_attr_fork(dp))
 		goto out_destroy_fork;
 	xfs_iunlock(dp, lock_mode);
 
@@ -351,7 +351,7 @@ xfs_attr_inactive(
 	lock_mode = XFS_ILOCK_EXCL;
 	xfs_ilock(dp, lock_mode);
 
-	if (!XFS_IFORK_Q(dp))
+	if (!xfs_inode_has_attr_fork(dp))
 		goto out_cancel;
 
 	/*
@@ -362,12 +362,11 @@ xfs_attr_inactive(
 
 	/*
 	 * Invalidate and truncate the attribute fork extents. Make sure the
-	 * fork actually has attributes as otherwise the invalidation has no
+	 * fork actually has xattr blocks as otherwise the invalidation has no
 	 * blocks to read and returns an error. In this case, just do the fork
 	 * removal below.
 	 */
-	if (xfs_inode_hasattr(dp) &&
-	    dp->i_afp->if_format != XFS_DINODE_FMT_LOCAL) {
+	if (dp->i_af.if_nextents > 0) {
 		error = xfs_attr3_root_inactive(&trans, dp);
 		if (error)
 			goto out_cancel;
@@ -388,11 +387,8 @@ out_cancel:
 	xfs_trans_cancel(trans);
 out_destroy_fork:
 	/* kill the in-core attr fork before we drop the inode lock */
-	if (dp->i_afp) {
-		xfs_idestroy_fork(dp->i_afp);
-		kmem_cache_free(xfs_ifork_cache, dp->i_afp);
-		dp->i_afp = NULL;
-	}
+	xfs_idestroy_fork(&dp->i_af);
+	xfs_ifork_zap_attr(dp);
 	if (lock_mode)
 		xfs_iunlock(dp, lock_mode);
 	return error;