Thanks! This looks good and reasonable. I'll try to get it pushed out to
-next in the next few days.
Shaggy
On 12/18/20 2:17 PM, Randy Dunlap wrote:
syzbot is feeding invalid superblock data to JFS for mount testing.
JFS does not check several of the fields -- just assumes that they
are good since the JFS_MAGIC and version fields are good.
In this case (syzbot reproducer), we have s_l2bsize == 0xda0c,
pad == 0xf045, and s_state == 0x50, all of which are invalid IMO.
Having s_l2bsize == 0xda0c causes this UBSAN warning:
UBSAN: shift-out-of-bounds in fs/jfs/jfs_mount.c:373:25
shift exponent -9716 is negative
s_l2bsize can be tested for correctness. pad can be tested for non-0
and punted. s_state can be tested for its valid values and punted.
Do those 3 tests and if any of them fails, report the superblock as
invalid/corrupt and let fsck handle it.
With this patch, chkSuper() says this when JFS_DEBUG is enabled:
jfs_mount: Mount Failure: superblock is corrupt!
Mount JFS Failure: -22
jfs_mount failed w/return code = -22
The obvious problem with this method is that next week there could
be another syzbot test that uses different fields for invalid values,
this making this like a game of whack-a-mole.
syzkaller link: https://syzkaller.appspot.com/bug?extid=36315852ece4132ec193
Reported-by: syzbot+36315852ece4132ec...@syzkaller.appspotmail.com
Reported-by: kernel test robot <l...@intel.com> # v2
Signed-off-by: Randy Dunlap <rdun...@infradead.org>
Cc: Dave Kleikamp <sha...@kernel.org>
Cc: jfs-discuss...@lists.sourceforge.net
---
v2: fix sparse __le32 warning (lkp robot)
fs/jfs/jfs_filsys.h | 1 +
fs/jfs/jfs_mount.c | 10 ++++++++++
2 files changed, 11 insertions(+)
--- lnx-510.orig/fs/jfs/jfs_mount.c
+++ lnx-510/fs/jfs/jfs_mount.c
@@ -37,6 +37,7 @@
#include <linux/fs.h>
#include <linux/buffer_head.h>
#include <linux/blkdev.h>
+#include <linux/log2.h>
#include "jfs_incore.h"
#include "jfs_filsys.h"
@@ -366,6 +367,15 @@ static int chkSuper(struct super_block *
sbi->bsize = bsize;
sbi->l2bsize = le16_to_cpu(j_sb->s_l2bsize);
+ /* check some fields for possible corruption */
+ if (sbi->l2bsize != ilog2((u32)bsize) ||
+ j_sb->pad != 0 ||
+ le32_to_cpu(j_sb->s_state) > FM_STATE_MAX) {
+ rc = -EINVAL;
+ jfs_err("jfs_mount: Mount Failure: superblock is corrupt!");
+ goto out;
+ }
+
/*
* For now, ignore s_pbsize, l2bfactor. All I/O going through buffer
* cache.
--- lnx-510.orig/fs/jfs/jfs_filsys.h
+++ lnx-510/fs/jfs/jfs_filsys.h
@@ -268,5 +268,6 @@
* fsck() must be run to repair
*/
#define FM_EXTENDFS 0x00000008 /* file system extendfs() in progress */
+#define FM_STATE_MAX 0x0000000f /* max value of s_state */
#endif /* _H_JFS_FILSYS */
