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

Eric Dumazet
2011-04-19T03:20:23Z

Le mardi 19 avril 2011 à 05:09 +0200, Eric Dumazet a écrit :
> Le mardi 19 avril 2011 à 04:51 +0200, Eric Dumazet a écrit :
>
> > Hmm, looking at mm/slub.c, I wonder what prevents "object" from pointing
> > to a now freed and unreachable zone of memory. (Say we are interrupted,
> > object given to interrupt handler and this one wants to change page bits
> > to trap access)
>
>
> Yes, I suspect this whole business is not kmemcheck compatable, or
> DEBUG_PAGEALLOC
>
> get_freepointer(s, object) can access to freed memory and kmemcheck
> triggers the fault, while this_cpu_cmpxchg_double() would presumably
> detect a change of tid and would not perform the freelist/tid change.
>
>
>

Christian, please try following patch, thanks

diff --git a/mm/slub.c b/mm/slub.c
index 94d2a33..84febe9 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(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.