[PATCH] net-ipv6: do not allow IPV6_TCLASS to muck with tcp's ECN

From: Maciej Żenczykowski <redacted>

This is to match ipv4 behaviour, see __ip_sock_set_tos()
implementation at ipv4/ip_sockglue.c:579

void __ip_sock_set_tos(struct sock *sk, int val)
{
  if (sk->sk_type == SOCK_STREAM) {
    val &= ~INET_ECN_MASK;
    val |= inet_sk(sk)->tos & INET_ECN_MASK;
  }
  if (inet_sk(sk)->tos != val) {
    inet_sk(sk)->tos = val;
    sk->sk_priority = rt_tos2priority(val);
    sk_dst_reset(sk);
  }
}

Cc: Eric Dumazet <edumazet@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Maciej Żenczykowski <redacted>
---
 net/ipv6/ipv6_sockglue.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
index 41efca817db4..204b0b4d10c8 100644
--- a/net/ipv6/ipv6_sockglue.c
+++ b/net/ipv6/ipv6_sockglue.c

@@ -599,6 +599,10 @@ static int do_ipv6_setsockopt(struct sock *sk, int level, int optname,
 		/* RFC 3542, 6.5: default traffic class of 0x0 */
 		if (val == -1)
 			val = 0;
+		if (sk->sk_type == SOCK_STREAM) {
+			val &= ~INET_ECN_MASK;
+			val |= np->tclass & INET_ECN_MASK;
+		}
 		np->tclass = val;
 		retv = 0;
 		break;

-- 
2.34.0.rc2.393.gf8c9666880-goog

On Tue, Nov 23, 2021 at 2:32 PM Maciej Żenczykowski
[off-list ref] wrote:

From: Maciej Żenczykowski <redacted>

This is to match ipv4 behaviour, see __ip_sock_set_tos()
implementation at ipv4/ip_sockglue.c:579

void __ip_sock_set_tos(struct sock *sk, int val)
{
  if (sk->sk_type == SOCK_STREAM) {
    val &= ~INET_ECN_MASK;
    val |= inet_sk(sk)->tos & INET_ECN_MASK;
  }
  if (inet_sk(sk)->tos != val) {
    inet_sk(sk)->tos = val;
    sk->sk_priority = rt_tos2priority(val);
    sk_dst_reset(sk);
  }
}

Cc: Eric Dumazet <edumazet@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Maciej Żenczykowski <redacted>

This makes sense, thanks, even if INET_ECN_dontxmit() would eventually
catch up for non dctcp.

Reviewed-by: Eric Dumazet <edumazet@google.com>

Hello:

This patch was applied to netdev/net-next.git (master)
by Jakub Kicinski [off-list ref]:

On Tue, 23 Nov 2021 14:31:54 -0800 you wrote:

From: Maciej Żenczykowski <redacted>

This is to match ipv4 behaviour, see __ip_sock_set_tos()
implementation at ipv4/ip_sockglue.c:579

void __ip_sock_set_tos(struct sock *sk, int val)
{
  if (sk->sk_type == SOCK_STREAM) {
    val &= ~INET_ECN_MASK;
    val |= inet_sk(sk)->tos & INET_ECN_MASK;
  }
  if (inet_sk(sk)->tos != val) {
    inet_sk(sk)->tos = val;
    sk->sk_priority = rt_tos2priority(val);
    sk_dst_reset(sk);
  }
}

[...]

Here is the summary with links:
  - net-ipv6: do not allow IPV6_TCLASS to muck with tcp's ECN
    https://git.kernel.org/netdev/net-next/c/9f7b3a69c88d

You are awesome, thank you!
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