slob: fix memory corruption

Previously, it would be possible for prev->next to point to
&free_slob_pages, and thus we would try to move a list onto itself, and
bad things would happen.

It seems a bit hairy to be doing list operations with the list marker as
an entry, rather than a head, but...

this resolves the following crash:

  http://bugzilla.kernel.org/show_bug.cgi?id=9379

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/mm/slob.c b/mm/slob.c
index 5bc2ceb692e..08a9bd91a1a 100644
--- a/mm/slob.c
+++ b/mm/slob.c
@@ -321,7 +321,8 @@ static void *slob_alloc(size_t size, gfp_t gfp, int align, int node)
                 /* Improve fragment distribution and reduce our average
                  * search time by starting our next search here. (see
                  * Knuth vol 1, sec 2.5, pg 449) */
-                if (free_slob_pages.next != prev->next)
+                if (prev != free_slob_pages.prev &&
+                                free_slob_pages.next != prev->next)
                         list_move_tail(&free_slob_pages, prev->next);
                 break;
         }