ipv4: add defensive check for CHECKSUM_PARTIAL skbs in ip_fragment

CHECKSUM_PARTIAL skbs should never arrive in ip_fragment. If we get one
of those warn about them once and handle them gracefully by recalculating
the checksum.

Cc: Eric Dumazet <edumazet@google.com>
Cc: Vlad Yasevich <vyasevich@gmail.com>
Cc: Benjamin Coddington <bcodding@redhat.com>
Cc: Tom Herbert <tom@herbertland.com>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 0b02417..4233cbe 100644 (file)
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -533,6 +533,11 @@ int ip_do_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 
        dev = rt->dst.dev;
 
+       /* for offloaded checksums cleanup checksum before fragmentation */
+       if (skb->ip_summed == CHECKSUM_PARTIAL &&
+           (err = skb_checksum_help(skb)))
+               goto fail;
+
        /*
         *      Point into the IP datagram header.
         */
@@ -657,9 +662,6 @@ slow_path_clean:
        }
 
 slow_path:
-       /* for offloaded checksums cleanup checksum before fragmentation */
-       if ((skb->ip_summed == CHECKSUM_PARTIAL) && skb_checksum_help(skb))
-               goto fail;
        iph = ip_hdr(skb);
 
        left = skb->len - hlen;         /* Space per frame */