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Date: Thu, 16 Jul 2009 14:05:02 +0200 From: Patrick McHardy <kaber@...sh.net> To: Eric Dumazet <eric.dumazet@...il.com> CC: David Miller <davem@...emloft.net>, netdev@...r.kernel.org, paulmck@...ux.vnet.ibm.com Subject: Re: [PATCH] net: nf_conntrack_alloc() fixes Eric Dumazet wrote: > [PATCH] net: nf_conntrack_alloc() fixes > > When a slab cache uses SLAB_DESTROY_BY_RCU, we must be careful when allocating > objects, since slab allocator could give a freed object still used by lockless > readers. > > In particular, nf_conntrack RCU lookups rely on ct->tuplehash[xxx].hnnode.next > being always valid (ie containing a valid 'nulls' value, or a valid pointer to next > object in hash chain.) > > kmem_cache_zalloc() setups object with NULL values, but a NULL value is not valid > for ct->tuplehash[xxx].hnnode.next. > > Fix is to call kmem_cache_alloc() and do the zeroing ourself. > > As spotted by Patrick, we also need to make sure lookup keys are committed to > memory before setting refcount to 1, or a lockless reader could get a reference > on the old version of the object. Its key re-check could then pass the barrier. Looks good to me. Applied, thanks Eric. I'll push it to -stable with the other fixes in a couple of days. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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