Commit fedbb6b4 authored by Shmulik Ladkani's avatar Shmulik Ladkani Committed by David S. Miller

ipv4: Fix ip_skb_dst_mtu to use the sk passed by ip_finish_output

ip_skb_dst_mtu uses skb->sk, assuming it is an AF_INET socket (e.g. it
calls ip_sk_use_pmtu which casts sk as an inet_sk).

However, in the case of UDP tunneling, the skb->sk is not necessarily an
inet socket (could be AF_PACKET socket, or AF_UNSPEC if arriving from

OTOH, the sk passed as an argument throughout IP stack's output path is
the one which is of PMTU interest:
 - In case of local sockets, sk is same as skb->sk;
 - In case of a udp tunnel, sk is the tunneling socket.

Fix, by passing ip_finish_output's sk to ip_skb_dst_mtu.
This augments 7026b1dd 'netfilter: Pass socket pointer down through okfn().'
Signed-off-by: default avatarShmulik Ladkani <>
Reviewed-by: default avatarHannes Frederic Sowa <>
Signed-off-by: default avatarDavid S. Miller <>
parent 5ab0d6a0
......@@ -313,10 +313,9 @@ static inline unsigned int ip_dst_mtu_maybe_forward(const struct dst_entry *dst,
return min(dst->dev->mtu, IP_MAX_MTU);
static inline unsigned int ip_skb_dst_mtu(const struct sk_buff *skb)
static inline unsigned int ip_skb_dst_mtu(struct sock *sk,
const struct sk_buff *skb)
struct sock *sk = skb->sk;
if (!sk || !sk_fullsock(sk) || ip_sk_use_pmtu(sk)) {
bool forwarding = IPCB(skb)->flags & IPSKB_FORWARDED;
......@@ -700,7 +700,7 @@ static int
br_nf_ip_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
int (*output)(struct net *, struct sock *, struct sk_buff *))
unsigned int mtu = ip_skb_dst_mtu(skb);
unsigned int mtu = ip_skb_dst_mtu(sk, skb);
struct iphdr *iph = ip_hdr(skb);
if (unlikely(((iph->frag_off & htons(IP_DF)) && !skb->ignore_df) ||
......@@ -271,7 +271,7 @@ static int ip_finish_output(struct net *net, struct sock *sk, struct sk_buff *sk
return dst_output(net, sk, skb);
mtu = ip_skb_dst_mtu(skb);
mtu = ip_skb_dst_mtu(sk, skb);
if (skb_is_gso(skb))
return ip_finish_output_gso(net, sk, skb, mtu);
......@@ -541,7 +541,7 @@ int ip_do_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
iph = ip_hdr(skb);
mtu = ip_skb_dst_mtu(skb);
mtu = ip_skb_dst_mtu(sk, skb);
if (IPCB(skb)->frag_max_size && IPCB(skb)->frag_max_size < mtu)
mtu = IPCB(skb)->frag_max_size;
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