releases/3.10.72/dm-snapshot-fix-a-possible-invalid-memory-access-on-unload.patch

   1 From 22aa66a3ee5b61e0f4a0bfeabcaa567861109ec3 Mon Sep 17 00:00:00 2001
   2 From: Mikulas Patocka <mpatocka@redhat.com>
   3 Date: Tue, 17 Feb 2015 14:34:00 -0500
   4 Subject: dm snapshot: fix a possible invalid memory access on unload
   5
   6 From: Mikulas Patocka <mpatocka@redhat.com>
   7
   8 commit 22aa66a3ee5b61e0f4a0bfeabcaa567861109ec3 upstream.
   9
  10 When the snapshot target is unloaded, snapshot_dtr() waits until
  11 pending_exceptions_count drops to zero.  Then, it destroys the snapshot.
  12 Therefore, the function that decrements pending_exceptions_count
  13 should not touch the snapshot structure after the decrement.
  14
  15 pending_complete() calls free_pending_exception(), which decrements
  16 pending_exceptions_count, and then it performs up_write(&s->lock) and it
  17 calls retry_origin_bios() which dereferences  s->origin.  These two
  18 memory accesses to the fields of the snapshot may touch the dm_snapshot
  19 struture after it is freed.
  20
  21 This patch moves the call to free_pending_exception() to the end of
  22 pending_complete(), so that the snapshot will not be destroyed while
  23 pending_complete() is in progress.
  24
  25 Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
  26 Signed-off-by: Mike Snitzer <snitzer@redhat.com>
  27 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  28
  29 ---
  30  drivers/md/dm-snap.c |    4 ++--
  31  1 file changed, 2 insertions(+), 2 deletions(-)
  32
  33 --- a/drivers/md/dm-snap.c
  34 +++ b/drivers/md/dm-snap.c
  35 @@ -1439,8 +1439,6 @@ out:
  36                 full_bio->bi_end_io = pe->full_bio_end_io;
  37                 full_bio->bi_private = pe->full_bio_private;
  38         }
  39 -       free_pending_exception(pe);
  40 -
  41         increment_pending_exceptions_done_count();
  42
  43         up_write(&s->lock);
  44 @@ -1457,6 +1455,8 @@ out:
  45         }
  46
  47         retry_origin_bios(s, origin_bios);
  48 +
  49 +       free_pending_exception(pe);
  50  }
  51
  52  static void commit_callback(void *context, int success)