bridge: Fix br_forward crash in promiscuous mode
From: Michael Braun <michael-dev@fami-braun.de>
bridge: Fix br_forward crash in promiscuous mode
It's a linux-next kernel from 2010-03-12 on an x86 system and it
OOPs in the bridge module in br_pass_frame_up (called by
br_handle_frame_finish) because brdev cannot be dereferenced (its set to
a non-null value).
Adding some BUG_ON statements revealed that
BR_INPUT_SKB_CB(skb)->brdev == br-dev
(as set in br_handle_frame_finish first)
only holds until br_forward is called.
The next call to br_pass_frame_up then fails.
Digging deeper it seems that br_forward either frees the skb or passes
it to NF_HOOK which will in turn take care of freeing the skb. The
same is holds for br_pass_frame_ip. So it seems as if two independent
skb allocations are required. As far as I can see, commit
b33084be192ee1e347d98bb5c9e38a53d98d35e2 ("bridge: Avoid unnecessary
clone on forward path") removed skb duplication and so likely causes
this crash. This crash does not happen on 2.6.33.
I've therefore modified br_forward the same way br_flood has been
modified so that the skb is not freed if skb0 is going to be used
and I can confirm that the attached patch resolves the issue for me.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/bridge/br_forward.c b/net/bridge/br_forward.c
index d61e6f7..8347916 100644
--- a/net/bridge/br_forward.c
+++ b/net/bridge/br_forward.c
@@ -19,6 +19,10 @@
#include <linux/netfilter_bridge.h>
#include "br_private.h"
+static int deliver_clone(struct net_bridge_port *prev, struct sk_buff *skb,
+ void (*__packet_hook)(const struct net_bridge_port *p,
+ struct sk_buff *skb));
+
/* Don't forward packets to originating port or forwarding diasabled */
static inline int should_deliver(const struct net_bridge_port *p,
const struct sk_buff *skb)
@@ -94,14 +98,18 @@
}
/* called with rcu_read_lock */
-void br_forward(const struct net_bridge_port *to, struct sk_buff *skb)
+void br_forward(const struct net_bridge_port *to, struct sk_buff *skb, struct sk_buff *skb0)
{
if (should_deliver(to, skb)) {
- __br_forward(to, skb);
+ if (skb0)
+ deliver_clone(to, skb, __br_forward);
+ else
+ __br_forward(to, skb);
return;
}
- kfree_skb(skb);
+ if (!skb0)
+ kfree_skb(skb);
}
static int deliver_clone(struct net_bridge_port *prev, struct sk_buff *skb,