xfs: fully initialize xfs_da_args in xchk_directory_blocks

While running the online fsck test suite, I noticed the following
assertion in the kernel log (edited for brevity):

XFS: Assertion failed: 0, file: fs/xfs/xfs_health.c, line: 571
------------[ cut here ]------------
WARNING: CPU: 3 PID: 11667 at fs/xfs/xfs_message.c:104 assfail+0x46/0x4a [xfs]
CPU: 3 PID: 11667 Comm: xfs_scrub Tainted: G        W         5.19.0-rc7-xfsx #rc7 6e6475eb29fd9dda3181f81b7ca7ff961d277a40
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1 04/01/2014
RIP: 0010:assfail+0x46/0x4a [xfs]
Call Trace:
 <TASK>
 xfs_dir2_isblock+0xcc/0xe0
 xchk_directory_blocks+0xc7/0x420
 xchk_directory+0x53/0xb0
 xfs_scrub_metadata+0x2b6/0x6b0
 xfs_scrubv_metadata+0x35e/0x4d0
 xfs_ioc_scrubv_metadata+0x111/0x160
 xfs_file_ioctl+0x4ec/0xef0
 __x64_sys_ioctl+0x82/0xa0
 do_syscall_64+0x2b/0x80
 entry_SYSCALL_64_after_hwframe+0x46/0xb0

This assertion triggers in xfs_dirattr_mark_sick when the caller passes
in a whichfork value that is neither of XFS_{DATA,ATTR}_FORK.  The cause
of this is that xchk_directory_blocks only partially initializes the
xfs_da_args structure that is passed to xfs_dir2_isblock.  If the data
fork is not correct, the XFS_IS_CORRUPT clause will trigger.  My
development branch reports this failure to the health monitoring
subsystem, which accesses the uninitialized args->whichfork field,
leading the the assertion tripping.  We really shouldn't be passing
random stack contents around, so the solution here is to force the
compiler to zero-initialize the struct.

Found by fuzzing u3.bmx[0].blockcount = middlebit on xfs/1554.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

1 files changed, 6 insertions, 4 deletions

diff --git a/fs/xfs/scrub/dir.c b/fs/xfs/scrub/dir.c
index 5c87800ab223..d1b0f23c2c59 100644
--- a/fs/xfs/scrub/dir.c
+++ b/fs/xfs/scrub/dir.c
@@ -666,7 +666,12 @@ xchk_directory_blocks(
 	struct xfs_scrub	*sc)
 {
 	struct xfs_bmbt_irec	got;
-	struct xfs_da_args	args;
+	struct xfs_da_args	args = {
+		.dp		= sc ->ip,
+		.whichfork	= XFS_DATA_FORK,
+		.geo		= sc->mp->m_dir_geo,
+		.trans		= sc->tp,
+	};
 	struct xfs_ifork	*ifp = xfs_ifork_ptr(sc->ip, XFS_DATA_FORK);
 	struct xfs_mount	*mp = sc->mp;
 	xfs_fileoff_t		leaf_lblk;
@@ -689,9 +694,6 @@ xchk_directory_blocks(
 	free_lblk = XFS_B_TO_FSB(mp, XFS_DIR2_FREE_OFFSET);
 
 	/* Is this a block dir? */
-	args.dp = sc->ip;
-	args.geo = mp->m_dir_geo;
-	args.trans = sc->tp;
 	error = xfs_dir2_isblock(&args, &is_block);
 	if (!xchk_fblock_process_error(sc, XFS_DATA_FORK, lblk, &error))
 		goto out;