From: Aya Levin ayal@nvidia.com
[ Upstream commit b210de4f8c97d57de051e805686248ec4c6cfc52 ]
There are cases where GSO segment's length exceeds the egress MTU: - Forwarding of a TCP GRO skb, when DF flag is not set. - Forwarding of an skb that arrived on a virtualisation interface (virtio-net/vhost/tap) with TSO/GSO size set by other network stack. - Local GSO skb transmitted on an NETIF_F_TSO tunnel stacked over an interface with a smaller MTU. - Arriving GRO skb (or GSO skb in a virtualised environment) that is bridged to a NETIF_F_TSO tunnel stacked over an interface with an insufficient MTU.
If so: - Consume the SKB and its segments. - Issue an ICMP packet with 'Packet Too Big' message containing the MTU, allowing the source host to reduce its Path MTU appropriately.
Note: These cases are handled in the same manner in IPv4 output finish. This patch aligns the behavior of IPv6 and the one of IPv4.
Fixes: 9e50849054a4 ("netfilter: ipv6: move POSTROUTING invocation before fragmentation") Signed-off-by: Aya Levin ayal@nvidia.com Reviewed-by: Tariq Toukan tariqt@nvidia.com Link: https://lore.kernel.org/r/1610027418-30438-1-git-send-email-ayal@nvidia.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/ipv6/ip6_output.c | 40 +++++++++++++++++++++++++++++++++++++++- 1 file changed, 39 insertions(+), 1 deletion(-)
--- a/net/ipv6/ip6_output.c +++ b/net/ipv6/ip6_output.c @@ -128,8 +128,42 @@ static int ip6_finish_output2(struct net return -EINVAL; }
+static int +ip6_finish_output_gso_slowpath_drop(struct net *net, struct sock *sk, + struct sk_buff *skb, unsigned int mtu) +{ + struct sk_buff *segs, *nskb; + netdev_features_t features; + int ret = 0; + + /* Please see corresponding comment in ip_finish_output_gso + * describing the cases where GSO segment length exceeds the + * egress MTU. + */ + features = netif_skb_features(skb); + segs = skb_gso_segment(skb, features & ~NETIF_F_GSO_MASK); + if (IS_ERR_OR_NULL(segs)) { + kfree_skb(skb); + return -ENOMEM; + } + + consume_skb(skb); + + skb_list_walk_safe(segs, segs, nskb) { + int err; + + skb_mark_not_on_list(segs); + err = ip6_fragment(net, sk, segs, ip6_finish_output2); + if (err && ret == 0) + ret = err; + } + + return ret; +} + static int ip6_finish_output(struct net *net, struct sock *sk, struct sk_buff *skb) { + unsigned int mtu; int ret;
ret = BPF_CGROUP_RUN_PROG_INET_EGRESS(sk, skb); @@ -146,7 +180,11 @@ static int ip6_finish_output(struct net } #endif
- if ((skb->len > ip6_skb_dst_mtu(skb) && !skb_is_gso(skb)) || + mtu = ip6_skb_dst_mtu(skb); + if (skb_is_gso(skb) && !skb_gso_validate_mtu(skb, mtu)) + return ip6_finish_output_gso_slowpath_drop(net, sk, skb, mtu); + + if ((skb->len > mtu && !skb_is_gso(skb)) || dst_allfrag(skb_dst(skb)) || (IP6CB(skb)->frag_max_size && skb->len > IP6CB(skb)->frag_max_size)) return ip6_fragment(net, sk, skb, ip6_finish_output2);