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, 14 insertions, 15 deletions

diff --git a/fs/xfs/libxfs/xfs_attr_leaf.c b/fs/xfs/libxfs/xfs_attr_leaf.c
index 8f47396f8dd2..5bd554b88d99 100644
--- a/fs/xfs/libxfs/xfs_attr_leaf.c
+++ b/fs/xfs/libxfs/xfs_attr_leaf.c
@@ -590,7 +590,7 @@ xfs_attr_shortform_bytesfit(
 	 * to real extents, or the delalloc conversion will take care of the
 	 * literal area rebalancing.
 	 */
-	if (bytes <= XFS_IFORK_ASIZE(dp))
+	if (bytes <= xfs_inode_attr_fork_size(dp))
 		return dp->i_forkoff;
 
 	/*
@@ -682,7 +682,7 @@ xfs_attr_shortform_create(
 	struct xfs_da_args	*args)
 {
 	struct xfs_inode	*dp = args->dp;
-	struct xfs_ifork	*ifp = dp->i_afp;
+	struct xfs_ifork	*ifp = &dp->i_af;
 	struct xfs_attr_sf_hdr	*hdr;
 
 	trace_xfs_attr_sf_create(args);
@@ -719,7 +719,7 @@ xfs_attr_sf_findname(
 	int			end;
 	int			i;
 
-	sf = (struct xfs_attr_shortform *)args->dp->i_afp->if_u1.if_data;
+	sf = (struct xfs_attr_shortform *)args->dp->i_af.if_u1.if_data;
 	sfe = &sf->list[0];
 	end = sf->hdr.count;
 	for (i = 0; i < end; sfe = xfs_attr_sf_nextentry(sfe),
@@ -764,7 +764,7 @@ xfs_attr_shortform_add(
 	mp = dp->i_mount;
 	dp->i_forkoff = forkoff;
 
-	ifp = dp->i_afp;
+	ifp = &dp->i_af;
 	ASSERT(ifp->if_format == XFS_DINODE_FMT_LOCAL);
 	sf = (struct xfs_attr_shortform *)ifp->if_u1.if_data;
 	if (xfs_attr_sf_findname(args, &sfe, NULL) == -EEXIST)
@@ -797,11 +797,10 @@ xfs_attr_fork_remove(
 	struct xfs_inode	*ip,
 	struct xfs_trans	*tp)
 {
-	ASSERT(ip->i_afp->if_nextents == 0);
+	ASSERT(ip->i_af.if_nextents == 0);
 
-	xfs_idestroy_fork(ip->i_afp);
-	kmem_cache_free(xfs_ifork_cache, ip->i_afp);
-	ip->i_afp = NULL;
+	xfs_idestroy_fork(&ip->i_af);
+	xfs_ifork_zap_attr(ip);
 	ip->i_forkoff = 0;
 	xfs_trans_log_inode(tp, ip, XFS_ILOG_CORE);
 }
@@ -825,7 +824,7 @@ xfs_attr_sf_removename(
 
 	dp = args->dp;
 	mp = dp->i_mount;
-	sf = (struct xfs_attr_shortform *)dp->i_afp->if_u1.if_data;
+	sf = (struct xfs_attr_shortform *)dp->i_af.if_u1.if_data;
 
 	error = xfs_attr_sf_findname(args, &sfe, &base);
 
@@ -889,7 +888,7 @@ xfs_attr_shortform_lookup(xfs_da_args_t *args)
 
 	trace_xfs_attr_sf_lookup(args);
 
-	ifp = args->dp->i_afp;
+	ifp = &args->dp->i_af;
 	ASSERT(ifp->if_format == XFS_DINODE_FMT_LOCAL);
 	sf = (struct xfs_attr_shortform *)ifp->if_u1.if_data;
 	sfe = &sf->list[0];
@@ -917,8 +916,8 @@ xfs_attr_shortform_getvalue(
 	struct xfs_attr_sf_entry *sfe;
 	int			i;
 
-	ASSERT(args->dp->i_afp->if_format == XFS_DINODE_FMT_LOCAL);
-	sf = (struct xfs_attr_shortform *)args->dp->i_afp->if_u1.if_data;
+	ASSERT(args->dp->i_af.if_format == XFS_DINODE_FMT_LOCAL);
+	sf = (struct xfs_attr_shortform *)args->dp->i_af.if_u1.if_data;
 	sfe = &sf->list[0];
 	for (i = 0; i < sf->hdr.count;
 				sfe = xfs_attr_sf_nextentry(sfe), i++) {
@@ -948,7 +947,7 @@ xfs_attr_shortform_to_leaf(
 	trace_xfs_attr_sf_to_leaf(args);
 
 	dp = args->dp;
-	ifp = dp->i_afp;
+	ifp = &dp->i_af;
 	sf = (struct xfs_attr_shortform *)ifp->if_u1.if_data;
 	size = be16_to_cpu(sf->hdr.totsize);
 	tmpbuffer = kmem_alloc(size, 0);
@@ -1055,8 +1054,8 @@ xfs_attr_shortform_verify(
 	int				i;
 	int64_t				size;
 
-	ASSERT(ip->i_afp->if_format == XFS_DINODE_FMT_LOCAL);
-	ifp = XFS_IFORK_PTR(ip, XFS_ATTR_FORK);
+	ASSERT(ip->i_af.if_format == XFS_DINODE_FMT_LOCAL);
+	ifp = xfs_ifork_ptr(ip, XFS_ATTR_FORK);
 	sfp = (struct xfs_attr_shortform *)ifp->if_u1.if_data;
 	size = ifp->if_bytes;