Re: [PATCH net] ipv6: tcp: drop silly ICMPv6 packet too big messages

On Thu, Jul 8, 2021 at 12:26 AM Martin KaFai Lau [off-list ref] wrote:

On Wed, Jul 07, 2021 at 08:46:30AM -0700, Eric Dumazet wrote:
[ ... ]

quoted

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 593c32fe57ed13a218492fd6056f2593e601ec79..bc334a6f24992c7b5b2c415eab4b6cf51bf36cb4 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c

@@ -348,11 +348,20 @@ static int tcp_v6_connect(struct sock *sk, struct sockaddr *uaddr,
 static void tcp_v6_mtu_reduced(struct sock *sk)
 {
      struct dst_entry *dst;
+     u32 mtu;

      if ((1 << sk->sk_state) & (TCPF_LISTEN | TCPF_CLOSE))
              return;

-     dst = inet6_csk_update_pmtu(sk, READ_ONCE(tcp_sk(sk)->mtu_info));
+     mtu = READ_ONCE(tcp_sk(sk)->mtu_info);
+
+     /* Drop requests trying to increase our current mss.
+      * Check done in __ip6_rt_update_pmtu() is too late.
+      */
+     if (tcp_mss_to_mtu(sk, mtu) >= tcp_sk(sk)->mss_cache)

Instead of tcp_mss_to_mtu, should this be calling tcp_mtu_to_mss to
compare with tcp_sk(sk)->mss_cache?

Good catch Martin, let me add and run a few more tests before sending a v2.

Thanks !