ext4: fix hang when processing corrupted orphaned inode list
authorTheodore Ts'o <tytso@mit.edu>
Sat, 30 Apr 2016 04:48:54 +0000 (00:48 -0400)
committerTheodore Ts'o <tytso@mit.edu>
Sat, 30 Apr 2016 04:48:54 +0000 (00:48 -0400)
commitc9eb13a9105e2e418f72e46a2b6da3f49e696902
treef7c98c4a9720744af5957c76b483a6f1ba0e7dd8
parent8d2ae1cbe8a984d7a755755fb53955de2f60a2f9
ext4: fix hang when processing corrupted orphaned inode list

If the orphaned inode list contains inode #5, ext4_iget() returns a
bad inode (since the bootloader inode should never be referenced
directly).  Because of the bad inode, we end up processing the inode
repeatedly and this hangs the machine.

This can be reproduced via:

   mke2fs -t ext4 /tmp/foo.img 100
   debugfs -w -R "ssv last_orphan 5" /tmp/foo.img
   mount -o loop /tmp/foo.img /mnt

(But don't do this if you are using an unpatched kernel if you care
about the system staying functional.  :-)

This bug was found by the port of American Fuzzy Lop into the kernel
to find file system problems[1].  (Since it *only* happens if inode #5
shows up on the orphan list --- 3, 7, 8, etc. won't do it, it's not
surprising that AFL needed two hours before it found it.)

[1] http://events.linuxfoundation.org/sites/events/files/slides/AFL%20filesystem%20fuzzing%2C%20Vault%202016_0.pdf

Cc: stable@vger.kernel.org
Reported by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
fs/ext4/ialloc.c