[PATCH] lib/list_sort: do not pass bad pointers to cmp callback

[Artem Bityutskiy <dedekind1@gmail.com>]

From: Don Mullis <don.mullis@gmail.com>

If the original list is a POT in length, the first callback from line 73 will
pass a==b both pointing to the original list_head. This is dangerous because
the 'list_sort()' user can use 'container_of()' and accesses the "containing"
object, which does not necessary exist for the list head. So the user can
access RAM which does not belong to him. If this is a write access, we can end
up with memory corruption. This patch fixes the issue.

Signed-off-by: Don Mullis <don.mullis@gmail.com>
Tested-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Cc: stable@kernel.org
---
 lib/list_sort.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/lib/list_sort.c b/lib/list_sort.c
index 4b5cb79..a7616fa 100644
--- a/lib/list_sort.c
+++ b/lib/list_sort.c
@@ -70,7 +70,7 @@ static void merge_and_restore_back_links(void *priv,
 		 * element comparison is needed, so the client's cmp()
 		 * routine can invoke cond_resched() periodically.
 		 */
-		(*cmp)(priv, tail, tail);
+		(*cmp)(priv, tail->next, tail->next);
 
 		tail->next->prev = tail;
 		tail = tail->next;
-- 
1.7.1.1


-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)