slob: fix memory corruption
authorNick Piggin <npiggin@suse.de>
Thu, 15 Nov 2007 11:32:04 +0000 (12:32 +0100)
committerLinus Torvalds <torvalds@woody.linux-foundation.org>
Thu, 15 Nov 2007 16:36:27 +0000 (08:36 -0800)
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>
mm/slob.c

index 5bc2ceb692ec94925340e0b65ce4cb8695e2cee1..08a9bd91a1aaf517f1b17ff688fa9f612273f873 100644 (file)
--- 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;
        }