4.14-stable patches

[thirdparty/kernel/stable-queue.git] / releases / 3.19.2 / dm-snapshot-fix-a-possible-invalid-memory-access-on-unload.patch

From 22aa66a3ee5b61e0f4a0bfeabcaa567861109ec3 Mon Sep 17 00:00:00 2001
From: Mikulas Patocka <mpatocka@redhat.com>
Date: Tue, 17 Feb 2015 14:34:00 -0500
Subject: dm snapshot: fix a possible invalid memory access on unload

From: Mikulas Patocka <mpatocka@redhat.com>

commit 22aa66a3ee5b61e0f4a0bfeabcaa567861109ec3 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/md/dm-snap.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -1432,8 +1432,6 @@ out:
 		full_bio->bi_private = pe->full_bio_private;
 		atomic_inc(&full_bio->bi_remaining);
 	}
-	free_pending_exception(pe);
-
 	increment_pending_exceptions_done_count();
 
 	up_write(&s->lock);
@@ -1450,6 +1448,8 @@ out:
 	}
 
 	retry_origin_bios(s, origin_bios);
+
+	free_pending_exception(pe);
 }
 
 static void commit_callback(void *context, int success)