Commit 22aa66a3 authored Feb 17, 2015 by Mikulas Patocka Committed by Mike Snitzer Feb 18, 2015

dm snapshot: fix a possible invalid memory access on unload



When the snapshot target is unloaded, snapshot_dtr() waits until
pending_exceptions_count drops to zero.  Then, it destroys the snapshot.
Therefore, the function that decrements pending_exceptions_count
should not touch the snapshot structure after the decrement.

pending_complete() calls free_pending_exception(), which decrements
pending_exceptions_count, and then it performs up_write(&s->lock) and it
calls retry_origin_bios() which dereferences  s->origin.  These two
memory accesses to the fields of the snapshot may touch the dm_snapshot
struture after it is freed.

This patch moves the call to free_pending_exception() to the end of
pending_complete(), so that the snapshot will not be destroyed while
pending_complete() is in progress.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org

parent 2bec1f4a

drivers/md/dm-snap.c

+2 −2

Original line number	Original line	Diff line number	Diff line
	@@ -1432,8 +1432,6 @@ static void pending_complete(struct dm_snap_pending_exception *pe, int success)
	full_bio->bi_private = pe->full_bio_private;		full_bio->bi_private = pe->full_bio_private;
	atomic_inc(&full_bio->bi_remaining);		atomic_inc(&full_bio->bi_remaining);
	}		}
	free_pending_exception(pe);

	increment_pending_exceptions_done_count();		increment_pending_exceptions_done_count();

	up_write(&s->lock);		up_write(&s->lock);
	@@ -1450,6 +1448,8 @@ static void pending_complete(struct dm_snap_pending_exception *pe, int success)
	}		}

	retry_origin_bios(s, origin_bios);		retry_origin_bios(s, origin_bios);

			free_pending_exception(pe);
	}		}

	static void commit_callback(void *context, int success)		static void commit_callback(void *context, int success)