netdev - [PATCH] netfilter: fix a race in nf_ct_ext

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Date:	Tue, 31 Aug 2010 17:48:02 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	Patrick McHardy <kaber@...sh.net>, netdev <netdev@...r.kernel.org>,
	Netfilter Development Mailinglist 
	<netfilter-devel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH] netfilter: fix a race in nf_ct_ext_create()

As soon as rcu_read_unlock() is called, there is no guarantee current
thread can safely derefence t pointer, rcu protected.

Fix is to copy t->alloc_size in a temporary variable.

Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
---
 net/netfilter/nf_conntrack_extend.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/netfilter/nf_conntrack_extend.c b/net/netfilter/nf_conntrack_extend.c
index 7dcf7a4..8d9e4c9 100644
--- a/net/netfilter/nf_conntrack_extend.c
+++ b/net/netfilter/nf_conntrack_extend.c
@@ -48,15 +48,17 @@ nf_ct_ext_create(struct nf_ct_ext **ext, enum nf_ct_ext_id id, gfp_t gfp)
 {
 	unsigned int off, len;
 	struct nf_ct_ext_type *t;
+	size_t alloc_size;
 
 	rcu_read_lock();
 	t = rcu_dereference(nf_ct_ext_types[id]);
 	BUG_ON(t == NULL);
 	off = ALIGN(sizeof(struct nf_ct_ext), t->align);
 	len = off + t->len;
+	alloc_size = t->alloc_size;
 	rcu_read_unlock();
 
-	*ext = kzalloc(t->alloc_size, gfp);
+	*ext = kzalloc(alloc_size, gfp);
 	if (!*ext)
 		return NULL;
 


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