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Commit fd27a0dc authored by Randy Dunlap's avatar Randy Dunlap Committed by Greg Kroah-Hartman
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JFS: more checks for invalid superblock 

commit 3bef198f1b17d1bb89260bad947ef084c0a2d1a6 upstream.

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: default avatar <syzbot+36315852ece4132ec193@syzkaller.appspotmail.com>
Reported-by: kernel test robot <lkp@intel.com> # v2
Signed-off-by: default avatarRandy Dunlap <rdunlap@infradead.org>
Signed-off-by: default avatarDave Kleikamp <dave.kleikamp@oracle.com>
Cc: jfs-discussion@lists.sourceforge.net
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 1d363ecd

fs/jfs/jfs_filsys.h

+1 −0
Original line number Diff line number Diff line
@@ -281,5 +281,6 @@ 
				 * 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 */

fs/jfs/jfs_mount.c

+10 −0
Original line number Diff line number Diff line
@@ -49,6 +49,7 @@ 


#include <linux/fs.h>

#include <linux/buffer_head.h>

#include <linux/log2.h>



#include "jfs_incore.h"

#include "jfs_filsys.h"
@@ -378,6 +379,15 @@ 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.