Re: mm: slub: invalid memory access in setup_object

Wei Yang
2014-07-02T02:05:06Z

On Tue, Jul 01, 2014 at 09:58:52AM -0500, Christoph Lameter wrote:
>On Mon, 30 Jun 2014, David Rientjes wrote:
>
>> It's not at all clear to me that that patch is correct. Wei?
>
>Looks ok to me. But I do not like the convoluted code in new_slab() which
>Wei's patch does not make easier to read. Makes it difficult for the
>reader to see whats going on.

My patch is somewhat convoluted since I wanted to preserve the original logic
and make minimal change. And yes, it looks not that nice to audience.

I feel a little hurt by this patch. What I found and worked is gone with this
patch.

>
>Lets drop the use of the variable named "last".
>
>
>Subject: slub: Only call setup_object once for each object
>
>Modify the logic for object initialization to be less convoluted
>and initialize an object only once.
>
>Signed-off-by: Christoph Lameter <cl@linux.com>
>
>Index: linux/mm/slub.c
>===================================================================
>--- linux.orig/mm/slub.c 2014-07-01 09:50:02.486846653 -0500
>+++ linux/mm/slub.c 2014-07-01 09:52:07.918802585 -0500
>@@ -1409,7 +1409,6 @@ static struct page *new_slab(struct kmem
> {
> struct page *page;
> void *start;
>- void *last;
> void *p;
> int order;
>
>@@ -1432,15 +1431,11 @@ static struct page *new_slab(struct kmem
> if (unlikely(s->flags & SLAB_POISON))
> memset(start, POISON_INUSE, PAGE_SIZE << order);
>
>- last = start;
> for_each_object(p, s, start, page->objects) {
>- setup_object(s, page, last);
>- set_freepointer(s, last, p);
>- last = p;
>+ setup_object(s, page, p);
>+ set_freepointer(s, p, p + s->size);
> }
>- setup_object(s, page, last);
>- set_freepointer(s, last, NULL);
>-
>+ set_freepointer(s, start + (page->objects - 1) * s->size, NULL);
> page->freelist = start;
> page->inuse = page->objects;
> page->frozen = 1;

--
Richard Yang
Help you, Help me