JFS: more checks for invalid superblock

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.

link: https://syzkaller.appspot.com/bug?extid=36315852ece4132ec193
Reported-by: syzbot+36315852ece4132ec193@syzkaller.appspotmail.com
Reported-by: kernel test robot <lkp@intel.com> # v2
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Cc: jfs-discussion@lists.sourceforge.net

diff --git a/fs/jfs/jfs_filsys.h b/fs/jfs/jfs_filsys.h
index 1e899298f7f00988d3400cff3fc9657f98c488ab..b5d702df7111a919a79f903ffe5462845deb4bd3 100644 (file)
--- a/fs/jfs/jfs_filsys.h
+++ b/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 */

diff --git a/fs/jfs/jfs_mount.c b/fs/jfs/jfs_mount.c
index 2935d4c776ec75e87980d6603b17181a2ab6f6e4..5d7d7170c03c0241b86c240a6f507d2a2b14b1e9 100644 (file)
--- a/fs/jfs/jfs_mount.c
+++ b/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 *sb)
        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.