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, 9 insertions, 11 deletions

diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
index 6b8857e53add..e28d93d232de 100644
--- a/fs/xfs/libxfs/xfs_attr.c
+++ b/fs/xfs/libxfs/xfs_attr.c
@@ -67,12 +67,10 @@ int
 xfs_inode_hasattr(
 	struct xfs_inode	*ip)
 {
-	if (!XFS_IFORK_Q(ip))
+	if (!xfs_inode_has_attr_fork(ip))
 		return 0;
-	if (!ip->i_afp)
-		return 0;
-	if (ip->i_afp->if_format == XFS_DINODE_FMT_EXTENTS &&
-	    ip->i_afp->if_nextents == 0)
+	if (ip->i_af.if_format == XFS_DINODE_FMT_EXTENTS &&
+	    ip->i_af.if_nextents == 0)
 		return 0;
 	return 1;
 }
@@ -85,7 +83,7 @@ bool
 xfs_attr_is_leaf(
 	struct xfs_inode	*ip)
 {
-	struct xfs_ifork	*ifp = ip->i_afp;
+	struct xfs_ifork	*ifp = &ip->i_af;
 	struct xfs_iext_cursor	icur;
 	struct xfs_bmbt_irec	imap;
 
@@ -231,7 +229,7 @@ xfs_attr_get_ilocked(
 	if (!xfs_inode_hasattr(args->dp))
 		return -ENOATTR;
 
-	if (args->dp->i_afp->if_format == XFS_DINODE_FMT_LOCAL)
+	if (args->dp->i_af.if_format == XFS_DINODE_FMT_LOCAL)
 		return xfs_attr_shortform_getvalue(args);
 	if (xfs_attr_is_leaf(args->dp))
 		return xfs_attr_leaf_get(args);
@@ -354,7 +352,7 @@ xfs_attr_try_sf_addname(
 	/*
 	 * Build initial attribute list (if required).
 	 */
-	if (dp->i_afp->if_format == XFS_DINODE_FMT_EXTENTS)
+	if (dp->i_af.if_format == XFS_DINODE_FMT_EXTENTS)
 		xfs_attr_shortform_create(args);
 
 	error = xfs_attr_shortform_addname(args);
@@ -864,7 +862,7 @@ xfs_attr_lookup(
 	if (!xfs_inode_hasattr(dp))
 		return -ENOATTR;
 
-	if (dp->i_afp->if_format == XFS_DINODE_FMT_LOCAL)
+	if (dp->i_af.if_format == XFS_DINODE_FMT_LOCAL)
 		return xfs_attr_sf_findname(args, NULL, NULL);
 
 	if (xfs_attr_is_leaf(dp)) {
@@ -1001,7 +999,7 @@ xfs_attr_set(
 		 * If the inode doesn't have an attribute fork, add one.
 		 * (inode must not be locked when we call this routine)
 		 */
-		if (XFS_IFORK_Q(dp) == 0) {
+		if (xfs_inode_has_attr_fork(dp) == 0) {
 			int sf_size = sizeof(struct xfs_attr_sf_hdr) +
 				xfs_attr_sf_entsize_byname(args->namelen,
 						args->valuelen);
@@ -1101,7 +1099,7 @@ static inline int xfs_attr_sf_totsize(struct xfs_inode *dp)
 {
 	struct xfs_attr_shortform *sf;
 
-	sf = (struct xfs_attr_shortform *)dp->i_afp->if_u1.if_data;
+	sf = (struct xfs_attr_shortform *)dp->i_af.if_u1.if_data;
 	return be16_to_cpu(sf->hdr.totsize);
 }