[PATCH] flow_dissector: prevent NULL pointer dereference in __skb_flow_dissect

[Anastasia Belova]

skb is an optional parameter, so it may be NULL.
Add check defore dereference in eth_hdr.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 67a900cc0436 ("flow_dissector: introduce support for Ethernet addresses")
Signed-off-by: Anastasia Belova <abelova@xxxxxxxxxxxxx>
---
 net/core/flow_dissector.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index 272f09251343..05db3a8aa771 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -1137,7 +1137,7 @@ bool __skb_flow_dissect(const struct net *net,
 		rcu_read_unlock();
 	}
 
-	if (dissector_uses_key(flow_dissector,
+	if (skb && dissector_uses_key(flow_dissector,
 			       FLOW_DISSECTOR_KEY_ETH_ADDRS)) {
 		struct ethhdr *eth = eth_hdr(skb);
 		struct flow_dissector_key_eth_addrs *key_eth_addrs;
-- 
2.30.2