[PATCH AUTOSEL for 4.15 095/124] xfs: harden directory integrity checks some more

Sasha Levin
2018-03-19T22:17:24Z

From: "Darrick J. Wong" <darrick.wong@oracle.com>

[ Upstream commit 46c59736d8090e602f960aeaf1c6b8292151bf38 ]

If a malicious filesystem image contains a block+ format directory
wherein the directory inode's core.mode is set such that
S_ISDIR(core.mode) == 0, and if there are subdirectories of the
corrupted directory, an attempt to traverse up the directory tree will
crash the kernel in __xfs_dir3_data_check. Running the online scrub's
parent checks will tend to do this.

The crash occurs because the directory inode's d_ops get set to
xfs_dir[23]_nondir_ops (it's not a directory) but the parent pointer
scrubber's indiscriminate call to xfs_readdir proceeds past the ASSERT
if we have non fatal asserts configured.

Fix the null pointer dereference crash in __xfs_dir3_data_check by
looking for S_ISDIR or wrong d_ops; and teach the parent scrubber
to bail out if it is fed a non-directory "parent".

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
fs/xfs/libxfs/xfs_dir2_data.c | 8 ++++++++
fs/xfs/scrub/parent.c | 2 +-
2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/libxfs/xfs_dir2_data.c b/fs/xfs/libxfs/xfs_dir2_data.c
index 8727a43115ef..700acc43289b 100644
--- a/fs/xfs/libxfs/xfs_dir2_data.c
+++ b/fs/xfs/libxfs/xfs_dir2_data.c
@@ -73,6 +73,14 @@ __xfs_dir3_data_check(
*/
ops = xfs_dir_get_ops(mp, dp);

+ /*
+ * If this isn't a directory, or we don't get handed the dir ops,
+ * something is seriously wrong. Bail out.
+ */
+ if ((dp && !S_ISDIR(VFS_I(dp)->i_mode)) ||
+ ops != xfs_dir_get_ops(mp, NULL))
+ return __this_address;
+
hdr = bp->b_addr;
p = (char *)ops->data_entry_p(hdr);

diff --git a/fs/xfs/scrub/parent.c b/fs/xfs/scrub/parent.c
index 63a25334fc83..b4d2f8406d22 100644
--- a/fs/xfs/scrub/parent.c
+++ b/fs/xfs/scrub/parent.c
@@ -171,7 +171,7 @@ xfs_scrub_parent_validate(
error = xfs_iget(mp, sc->tp, dnum, 0, 0, &dp);
if (!xfs_scrub_fblock_process_error(sc, XFS_DATA_FORK, 0, &error))
goto out;
- if (dp == sc->ip) {
+ if (dp == sc->ip || !S_ISDIR(VFS_I(dp)->i_mode)) {
xfs_scrub_fblock_set_corrupt(sc, XFS_DATA_FORK, 0);
goto out_rele;
}
--
2.14.1