Fix UDP header pointer after pskb_trim_rcsum()

[UDP]: Reread uh pointer after pskb_trim

The header may have moved when trimming.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

net/ipv4/udp.c

@@ -1214,6 +1214,7 @@ int __udp4_lib_rcv(struct sk_buff *skb, struct hlist_head udptable[],
 
 		if (ulen < sizeof(*uh) || pskb_trim_rcsum(skb, ulen))
 			goto short_packet;
+		uh = skb->h.uh;
 
 		udp4_csum_init(skb, uh);