Merge branch 'net-fix-skb-unclone-issues'

Antoine Tenart says:

====================
net: fix issues when uncloning an skb dst+metadata

This fixes two issues when uncloning an skb dst+metadata in
tun_dst_unclone; this was initially reported by Vlad Buslov[1]. Because
of the memory leak fixed by patch 2, the issue in patch 1 never happened
in practice.

tun_dst_unclone is called from two different places, one in geneve/vxlan
to handle PMTU and one in net/openvswitch/actions.c where it is used to
retrieve tunnel information. While both Vlad and I tested the former, we
could not for the latter. I did spend quite some time trying to, but
that code path is not easy to trigger. Code inspection shows this should
be fine, the tunnel information (dst+metadata) is uncloned and the skb
it is referenced from is only consumed after all accesses to the tunnel
information are done:

  do_execute_actions
    output_userspace
      dev_fill_metadata_dst         <- dst+metadata is uncloned
      ovs_dp_upcall
        queue_userspace_packet
          ovs_nla_put_tunnel_info   <- metadata (tunnel info) is accessed
    consume_skb                     <- dst+metadata is freed

Thanks!
Antoine

[1] https://lore.kernel.org/all/ygnhh79yluw2.fsf@nvidia.com/T/#m2f814614a4f5424cea66bbff7297f692b59b69a0
====================
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/dst_metadata.h

@@ -123,8 +123,20 @@ static inline struct metadata_dst *tun_dst_unclone(struct sk_buff *skb)
 
 	memcpy(&new_md->u.tun_info, &md_dst->u.tun_info,
 	       sizeof(struct ip_tunnel_info) + md_size);
+#ifdef CONFIG_DST_CACHE
+	/* Unclone the dst cache if there is one */
+	if (new_md->u.tun_info.dst_cache.cache) {
+		int ret;
+
+		ret = dst_cache_init(&new_md->u.tun_info.dst_cache, GFP_ATOMIC);
+		if (ret) {
+			metadata_dst_free(new_md);
+			return ERR_PTR(ret);
+		}
+	}
+#endif
+
 	skb_dst_drop(skb);
-	dst_hold(&new_md->dst);
 	skb_dst_set(skb, &new_md->dst);
 	return new_md;
 }