netdev - Re: [Bugme-new] [Bug 27212] New: Warning kmemcheck: Caught 64-bit read from uninitialized memory in netlink_broadcast

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Date:	Mon, 14 Feb 2011 18:35:22 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Pekka Enberg <penberg@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, netdev@...r.kernel.org,
	bugzilla-daemon@...zilla.kernel.org,
	bugme-daemon@...zilla.kernel.org, casteyde.christian@...e.fr,
	Changli Gao <xiaosuo@...il.com>,
	Vegard Nossum <vegardno@....uio.no>,
	David Miller <davem@...emloft.net>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [Bugme-new] [Bug 27212] New: Warning kmemcheck: Caught 64-bit
 read from uninitialized memory in netlink_broadcast_filtered

Le vendredi 21 janvier 2011 à 09:49 +0200, Pekka Enberg a écrit :

> It actually looks like a bug in SLUB+kmemcheck. The 
> kmemcheck_slab_alloc() call in slab_post_alloc_hook() should use ksize() 
> instead of s->objsize. SLAB seems to do the right thing already. Anyone 
> care to send a patch my way?
> 

Hmm, what do you think of following patch ?

Thanks, and sorry for the delay.

[PATCH] slub: fix kmemcheck calls to match ksize() hints

Recent use of ksize() in network stack (commit ca44ac38 : net: don't
reallocate skb->head unless the current one hasn't the needed extra size
or is shared) triggers kmemcheck warnings, because ksize() can return
more space than kmemcheck is aware of.

Pekka Enberg noticed SLAB+kmemcheck is doing the right thing, while SLUB
+kmemcheck doesnt.

Bugzilla reference #27212

Reported-by: Christian Casteyde <casteyde.christian@...e.fr>
Suggested-by: Pekka Enberg <penberg@...nel.org>
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
CC: David Miller <davem@...emloft.net>
CC: Changli Gao <xiaosuo@...il.com>
CC: Andrew Morton <akpm@...ux-foundation.org>
---
 mm/slub.c |   49 ++++++++++++++++++++++++++-----------------------
 1 file changed, 26 insertions(+), 23 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index e15aa7f..ee0aeb8 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -797,10 +797,34 @@ static inline int slab_pre_alloc_hook(struct kmem_cache *s, gfp_t flags)
 	return should_failslab(s->objsize, flags, s->flags);
 }
 
+static inline size_t slab_ksize(const struct kmem_cache *s)
+{
+#ifdef CONFIG_SLUB_DEBUG
+	/*
+	 * Debugging requires use of the padding between object
+	 * and whatever may come after it.
+	 */
+	if (s->flags & (SLAB_RED_ZONE | SLAB_POISON))
+		return s->objsize;
+
+#endif
+	/*
+	 * If we have the need to store the freelist pointer
+	 * back there or track user information then we can
+	 * only use the space before that information.
+	 */
+	if (s->flags & (SLAB_DESTROY_BY_RCU | SLAB_STORE_USER))
+		return s->inuse;
+	/*
+	 * Else we can use all the padding etc for the allocation
+	 */
+	return s->size;
+}
+
 static inline void slab_post_alloc_hook(struct kmem_cache *s, gfp_t flags, void *object)
 {
 	flags &= gfp_allowed_mask;
-	kmemcheck_slab_alloc(s, flags, object, s->objsize);
+	kmemcheck_slab_alloc(s, flags, object, slab_ksize(s));
 	kmemleak_alloc_recursive(object, s->objsize, 1, s->flags, flags);
 }
 
@@ -2696,7 +2720,6 @@ EXPORT_SYMBOL(__kmalloc_node);
 size_t ksize(const void *object)
 {
 	struct page *page;
-	struct kmem_cache *s;
 
 	if (unlikely(object == ZERO_SIZE_PTR))
 		return 0;
@@ -2707,28 +2730,8 @@ size_t ksize(const void *object)
 		WARN_ON(!PageCompound(page));
 		return PAGE_SIZE << compound_order(page);
 	}
-	s = page->slab;
 
-#ifdef CONFIG_SLUB_DEBUG
-	/*
-	 * Debugging requires use of the padding between object
-	 * and whatever may come after it.
-	 */
-	if (s->flags & (SLAB_RED_ZONE | SLAB_POISON))
-		return s->objsize;
-
-#endif
-	/*
-	 * If we have the need to store the freelist pointer
-	 * back there or track user information then we can
-	 * only use the space before that information.
-	 */
-	if (s->flags & (SLAB_DESTROY_BY_RCU | SLAB_STORE_USER))
-		return s->inuse;
-	/*
-	 * Else we can use all the padding etc for the allocation
-	 */
-	return s->size;
+	return slab_ksize(page->slab);
 }
 EXPORT_SYMBOL(ksize);
 


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