udp: Fix potential wrong ip_hdr(skb) pointers

Like the UDP header fix, pskb_may_pull() can potentially
alter the SKB buffer.  Thus the saddr and daddr, pointers
may point to the old skb->data buffer.

I haven't seen corruptions, as its only seen if the old
skb->data buffer were reallocated by another user and
written into very quickly (or poison'd by SLAB debugging).

Signed-off-by: Jesper Dangaard Brouer <hawk@comx.dk>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 2 deletions

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index cc3a0a06c004..c47c989cb1fb 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1234,8 +1234,7 @@ int __udp4_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
         struct udphdr *uh;
         unsigned short ulen;
         struct rtable *rt = (struct rtable*)skb->dst;
-        __be32 saddr = ip_hdr(skb)->saddr;
-        __be32 daddr = ip_hdr(skb)->daddr;
+        __be32 saddr, daddr;
         struct net *net = dev_net(skb->dev);
 
         /*
@@ -1259,6 +1258,9 @@ int __udp4_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
         if (udp4_csum_init(skb, uh, proto))
                 goto csum_error;
 
+        saddr = ip_hdr(skb)->saddr;
+        daddr = ip_hdr(skb)->daddr;
+
         if (rt->rt_flags & (RTCF_BROADCAST|RTCF_MULTICAST))
                 return __udp4_lib_mcast_deliver(net, skb, uh,
                                 saddr, daddr, udptable);