udp: Fix UDP short packet false positive

[ Upstream commit 7b5e56f9d635643ad54f2f42e69ad16b80a2cff1 ]

The UDP header pointer assignment must happen after calling
pskb_may_pull().  As pskb_may_pull() can potentially alter the SKB
buffer.

This was exposted by running multicast traffic through the NIU driver,
as it won't prepull the protocol headers into the linear area on
receive.

Signed-off-by: Jesper Dangaard Brouer <hawk@comx.dk>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 915e6b7ad7fd3fa3a38d5ad1bcc68d83da5ac223..f4ccd672d11b39b8bda333cc66033015983f6702 100644 (file)
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1172,7 +1172,7 @@ int __udp4_lib_rcv(struct sk_buff *skb, struct hlist_head udptable[],
                   int proto)
 {
        struct sock *sk;
-       struct udphdr *uh = udp_hdr(skb);
+       struct udphdr *uh;
        unsigned short ulen;
        struct rtable *rt = (struct rtable*)skb->dst;
        __be32 saddr = ip_hdr(skb)->saddr;
@@ -1185,6 +1185,7 @@ int __udp4_lib_rcv(struct sk_buff *skb, struct hlist_head udptable[],
        if (!pskb_may_pull(skb, sizeof(struct udphdr)))
                goto drop;              /* No space for header. */
 
+       uh   = udp_hdr(skb);
        ulen = ntohs(uh->len);
        if (ulen > skb->len)
                goto short_packet;