netdev - Re: [PATCH net-next 1/2] tcp: conditionally call ip_icmp_error() from tcp_v4

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Message-ID: <CANP3RGceOxPAMWi2S2uV6MHSh0BX-tPM9XmaoPy0QwOOF_KFvw@mail.gmail.com>
Date: Wed, 17 Apr 2024 10:08:39 -0700
From: Maciej Żenczykowski <maze@...gle.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org, 
	Neal Cardwell <ncardwell@...gle.com>, Dragos Tatulea <dtatulea@...dia.com>, eric.dumazet@...il.com, 
	Willem de Bruijn <willemb@...gle.com>, Shachar Kagan <skagan@...dia.com>
Subject: Re: [PATCH net-next 1/2] tcp: conditionally call ip_icmp_error() from tcp_v4_err()

On Wed, Apr 17, 2024 at 9:58 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> Blamed commit claimed in its changelog that the new functionality
> was guarded by IP_RECVERR/IPV6_RECVERR :
>
>     Note that applications need to set IP_RECVERR/IPV6_RECVERR option to
>     enable this feature, and that the error message is only queued
>     while in SYN_SNT state.
>
> This was true only for IPv6, because ipv6_icmp_error() has
> the following check:
>
> if (!inet6_test_bit(RECVERR6, sk))
>     return;
>
> Other callers check IP_RECVERR by themselves, it is unclear
> if we could factorize these checks in ip_icmp_error()
>
> For stable backports, I chose to add the missing check in tcp_v4_err()
>
> We think this missing check was the root cause for commit
> 0a8de364ff7a ("tcp: no longer abort SYN_SENT when receiving
> some ICMP") breakage, leading to a revert.
>
> Many thanks to Dragos Tatulea for conducting the investigations.
>
> As Jakub said :
>
>     The suspicion is that SSH sees the ICMP report on the socket error queue
>     and tries to connect() again, but due to the patch the socket isn't
>     disconnected, so it gets EALREADY, and throws its hands up...
>
>     The error bubbles up to Vagrant which also becomes unhappy.
>
>     Can we skip the call to ip_icmp_error() for non-fatal ICMP errors?
>
> Fixes: 45af29ca761c ("tcp: allow traceroute -Mtcp for unpriv users")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Tested-by: Dragos Tatulea <dtatulea@...dia.com>
> Cc: Dragos Tatulea <dtatulea@...dia.com>
> Cc: Maciej Żenczykowski <maze@...gle.com>
> Cc: Willem de Bruijn <willemb@...gle.com>
> Cc: Neal Cardwell <ncardwell@...gle.com>
> Cc: Shachar Kagan <skagan@...dia.com>
> ---
>  net/ipv4/tcp_ipv4.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index 88c83ac4212957f19efad0f967952d2502bdbc7f..a717db99972d977a64178d7ed1109325d64a6d51 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -602,7 +602,8 @@ int tcp_v4_err(struct sk_buff *skb, u32 info)
>                 if (fastopen && !fastopen->sk)
>                         break;
>
> -               ip_icmp_error(sk, skb, err, th->dest, info, (u8 *)th);
> +               if (inet_test_bit(RECVERR, sk))
> +                       ip_icmp_error(sk, skb, err, th->dest, info, (u8 *)th);
>
>                 if (!sock_owned_by_user(sk)) {
>                         WRITE_ONCE(sk->sk_err, err);
> --
> 2.44.0.683.g7961c838ac-goog
>

Reviewed-by: Maciej Żenczykowski <maze@...gle.com>

Makes sense to me.