net: ipv4: Don't crash if passing a null sk to ip_rt_update_pmtu.

Commit e2d118a1cb5e ("net: inet: Support UID-based routing in IP
protocols.") made __build_flow_key call sock_net(sk) to determine
the network namespace of the passed-in socket. This crashes if sk
is NULL.

Fix this by getting the network namespace from the skb instead.

[Backport of net-next d109e61bfe7a468fd8df4a7ceb65635e7aa909a0]

Bug: 16355602
Change-Id: I23b43db5adb8546833e013c268f31111d0e53c69
Fixes: e2d118a1cb5e ("net: inet: Support UID-based routing in IP protocols.")
Reported-by: Erez Shitrit <erezsh@dev.mellanox.co.il>
Signed-off-by: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 292c08985b0f5e055e5ebec6a0327b7419f7a818..4f3c789cb77e71c9aac79b380a00100588903599 100644 (file)
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -539,13 +539,14 @@ static void __build_flow_key(const struct net *net, struct flowi4 *fl4,
 static void build_skb_flow_key(struct flowi4 *fl4, const struct sk_buff *skb,
                               const struct sock *sk)
 {
+       const struct net *net = dev_net(skb->dev);
        const struct iphdr *iph = ip_hdr(skb);
        int oif = skb->dev->ifindex;
        u8 tos = RT_TOS(iph->tos);
        u8 prot = iph->protocol;
        u32 mark = skb->mark;
 
-       __build_flow_key(sock_net(sk), fl4, sk, iph, oif, tos, prot, mark, 0);
+       __build_flow_key(net, fl4, sk, iph, oif, tos, prot, mark, 0);
 }
 
 static void build_sk_flow_key(struct flowi4 *fl4, const struct sock *sk)