Re: [Bugme-new] [Bug 33502] New: Caught 64-bit read from uninitialized memory in __alloc_skb

Eric Dumazet
2011-05-05T06:18:25Z

Le mercredi 20 avril 2011 à 17:01 +0200, Eric Dumazet a écrit :
> Le mercredi 20 avril 2011 à 09:42 -0500, Christoph Lameter a écrit :
>
> > Avoiding the irq handling yields the savings that improve the fastpath. if
> > you do both then there is only a regression left. So lets go with
> > disabling the CMPXCHG_LOCAL.
>
> OK, let's do that then.
>
> Thanks
>
> [PATCH v4] slub: dont use cmpxchg_double if KMEMCHECK or DEBUG_PAGEALLOC
>
> Christian Casteyde reported a KMEMCHECK splat in slub code.
>
> Problem is now we are lockless and allow IRQ in slab_alloc(), the object
> we manipulate from freelist can be allocated and freed right before we
> try to read object->next.
>
> Same problem can happen with DEBUG_PAGEALLOC
>
> Just dont use cmpxchg_double() if either CONFIG_KMEMCHECK or
> CONFIG_DEBUG_PAGEALLOC is defined.
>
> Reported-by: Christian Casteyde <casteyde.christian@free.fr>
> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Pekka Enberg <penberg@cs.helsinki.fi>
> Cc: Vegard Nossum <vegardno@ifi.uio.no>
> Cc: Christoph Lameter <cl@linux.com>
> ---
> mm/slub.c | 45 +++++++++++++++++++++++++--------------------
> 1 files changed, 25 insertions(+), 20 deletions(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 94d2a33..f31ab2c 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1540,7 +1540,12 @@ static void unfreeze_slab(struct kmem_cache *s, struct page *page, int tail)
> }
> }
>
> -#ifdef CONFIG_CMPXCHG_LOCAL
> +#if defined(CONFIG_CMPXCHG_LOCAL) && !defined(CONFIG_KMEMCHECK) && \
> + !defined(CONFIG_DEBUG_PAGEALLOC)
> +#define SLUB_USE_CMPXCHG_DOUBLE
> +#endif
> +
> +#ifdef SLUB_USE_CMPXCHG_DOUBLE
> #ifdef CONFIG_PREEMPT
> /*
> * Calculate the next globally unique transaction for disambiguiation
> @@ -1604,7 +1609,7 @@ static inline void note_cmpxchg_failure(const char *n,
>
> void init_kmem_cache_cpus(struct kmem_cache *s)
> {
> -#ifdef CONFIG_CMPXCHG_LOCAL
> +#ifdef SLUB_USE_CMPXCHG_DOUBLE
> int cpu;
>
> for_each_possible_cpu(cpu)
> @@ -1643,7 +1648,7 @@ static void deactivate_slab(struct kmem_cache *s, struct kmem_cache_cpu *c)
> page->inuse--;
> }
> c->page = NULL;
> -#ifdef CONFIG_CMPXCHG_LOCAL
> +#ifdef SLUB_USE_CMPXCHG_DOUBLE
> c->tid = next_tid(c->tid);
> #endif
> unfreeze_slab(s, page, tail);
> @@ -1780,7 +1785,7 @@ static void *__slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
> {
> void **object;
> struct page *new;
> -#ifdef CONFIG_CMPXCHG_LOCAL
> +#ifdef SLUB_USE_CMPXCHG_DOUBLE
> unsigned long flags;
>
> local_irq_save(flags);
> @@ -1819,7 +1824,7 @@ load_freelist:
> c->node = page_to_nid(c->page);
> unlock_out:
> slab_unlock(c->page);
> -#ifdef CONFIG_CMPXCHG_LOCAL
> +#ifdef SLUB_USE_CMPXCHG_DOUBLE
> c->tid = next_tid(c->tid);
> local_irq_restore(flags);
> #endif
> @@ -1858,7 +1863,7 @@ new_slab:
> }
> if (!(gfpflags & __GFP_NOWARN) && printk_ratelimit())
> slab_out_of_memory(s, gfpflags, node);
> -#ifdef CONFIG_CMPXCHG_LOCAL
> +#ifdef SLUB_USE_CMPXCHG_DOUBLE
> local_irq_restore(flags);
> #endif
> return NULL;
> @@ -1887,7 +1892,7 @@ static __always_inline void *slab_alloc(struct kmem_cache *s,
> {
> void **object;
> struct kmem_cache_cpu *c;
> -#ifdef CONFIG_CMPXCHG_LOCAL
> +#ifdef SLUB_USE_CMPXCHG_DOUBLE
> unsigned long tid;
> #else
> unsigned long flags;
> @@ -1896,7 +1901,7 @@ static __always_inline void *slab_alloc(struct kmem_cache *s,
> if (slab_pre_alloc_hook(s, gfpflags))
> return NULL;
>
> -#ifndef CONFIG_CMPXCHG_LOCAL
> +#ifndef SLUB_USE_CMPXCHG_DOUBLE
> local_irq_save(flags);
> #else
> redo:
> @@ -1910,7 +1915,7 @@ redo:
> */
> c = __this_cpu_ptr(s->cpu_slab);
>
> -#ifdef CONFIG_CMPXCHG_LOCAL
> +#ifdef SLUB_USE_CMPXCHG_DOUBLE
> /*
> * The transaction ids are globally unique per cpu and per operation on
> * a per cpu queue. Thus they can be guarantee that the cmpxchg_double
> @@ -1927,7 +1932,7 @@ redo:
> object = __slab_alloc(s, gfpflags, node, addr, c);
>
> else {
> -#ifdef CONFIG_CMPXCHG_LOCAL
> +#ifdef SLUB_USE_CMPXCHG_DOUBLE
> /*
> * The cmpxchg will only match if there was no additional
> * operation and if we are on the right processor.
> @@ -1954,7 +1959,7 @@ redo:
> stat(s, ALLOC_FASTPATH);
> }
>
> -#ifndef CONFIG_CMPXCHG_LOCAL
> +#ifndef SLUB_USE_CMPXCHG_DOUBLE
> local_irq_restore(flags);
> #endif
>
> @@ -2034,7 +2039,7 @@ static void __slab_free(struct kmem_cache *s, struct page *page,
> {
> void *prior;
> void **object = (void *)x;
> -#ifdef CONFIG_CMPXCHG_LOCAL
> +#ifdef SLUB_USE_CMPXCHG_DOUBLE
> unsigned long flags;
>
> local_irq_save(flags);
> @@ -2070,7 +2075,7 @@ checks_ok:
>
> out_unlock:
> slab_unlock(page);
> -#ifdef CONFIG_CMPXCHG_LOCAL
> +#ifdef SLUB_USE_CMPXCHG_DOUBLE
> local_irq_restore(flags);
> #endif
> return;
> @@ -2084,7 +2089,7 @@ slab_empty:
> stat(s, FREE_REMOVE_PARTIAL);
> }
> slab_unlock(page);
> -#ifdef CONFIG_CMPXCHG_LOCAL
> +#ifdef SLUB_USE_CMPXCHG_DOUBLE
> local_irq_restore(flags);
> #endif
> stat(s, FREE_SLAB);
> @@ -2113,7 +2118,7 @@ static __always_inline void slab_free(struct kmem_cache *s,
> {
> void **object = (void *)x;
> struct kmem_cache_cpu *c;
> -#ifdef CONFIG_CMPXCHG_LOCAL
> +#ifdef SLUB_USE_CMPXCHG_DOUBLE
> unsigned long tid;
> #else
> unsigned long flags;
> @@ -2121,7 +2126,7 @@ static __always_inline void slab_free(struct kmem_cache *s,
>
> slab_free_hook(s, x);
>
> -#ifndef CONFIG_CMPXCHG_LOCAL
> +#ifndef SLUB_USE_CMPXCHG_DOUBLE
> local_irq_save(flags);
>
> #else
> @@ -2136,7 +2141,7 @@ redo:
> */
> c = __this_cpu_ptr(s->cpu_slab);
>
> -#ifdef CONFIG_CMPXCHG_LOCAL
> +#ifdef SLUB_USE_CMPXCHG_DOUBLE
> tid = c->tid;
> barrier();
> #endif
> @@ -2144,7 +2149,7 @@ redo:
> if (likely(page == c->page && c->node != NUMA_NO_NODE)) {
> set_freepointer(s, object, c->freelist);
>
> -#ifdef CONFIG_CMPXCHG_LOCAL
> +#ifdef SLUB_USE_CMPXCHG_DOUBLE
> if (unlikely(!this_cpu_cmpxchg_double(
> s->cpu_slab->freelist, s->cpu_slab->tid,
> c->freelist, tid,
> @@ -2160,7 +2165,7 @@ redo:
> } else
> __slab_free(s, page, x, addr);
>
> -#ifndef CONFIG_CMPXCHG_LOCAL
> +#ifndef SLUB_USE_CMPXCHG_DOUBLE
> local_irq_restore(flags);
> #endif
> }
> @@ -2354,7 +2359,7 @@ static inline int alloc_kmem_cache_cpus(struct kmem_cache *s)
> BUILD_BUG_ON(PERCPU_DYNAMIC_EARLY_SIZE <
> SLUB_PAGE_SHIFT * sizeof(struct kmem_cache_cpu));
>
> -#ifdef CONFIG_CMPXCHG_LOCAL
> +#ifdef SLUB_USE_CMPXCHG_DOUBLE
> /*
> * Must align to double word boundary for the double cmpxchg instructions
> * to work.
>

Is anybody taking the patch and sending it upstream ?

Thanks