ipv4: use ip_skb_dst_mtu to determine mtu in ip_fragment

ip_skb_dst_mtu mostly falls back to ip_dst_mtu_maybe_forward if no socket
is attached to the skb (in case of forwarding) or determines the mtu like
we do in ip_finish_output, which actually checks if we should branch to
ip_fragment. Thus use the same function to determine the mtu here, too.

This is important for the introduction of IP_PMTUDISC_OMIT, where we
want the packets getting cut in pieces of the size of the outgoing
interface mtu. IPv6 already does this correctly.

Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 2 deletions

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 8971780aec7c..22aa11971ed1 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -449,7 +449,6 @@ int ip_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
         __be16 not_last_frag;
         struct rtable *rt = skb_rtable(skb);
         int err = 0;
-        bool forwarding = IPCB(skb)->flags & IPSKB_FORWARDED;
 
         dev = rt->dst.dev;
 
@@ -459,7 +458,7 @@ int ip_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
 
         iph = ip_hdr(skb);
 
-        mtu = ip_dst_mtu_maybe_forward(&rt->dst, forwarding);
+        mtu = ip_skb_dst_mtu(skb);
         if (unlikely(((iph->frag_off & htons(IP_DF)) && !skb->local_df) ||
                      (IPCB(skb)->frag_max_size &&
                       IPCB(skb)->frag_max_size > mtu))) {