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

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Date: Thu, 18 Apr 2024 08:45:34 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Jason Xing <kerneljasonxing@...il.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, 
	Maciej Żenczykowski <maze@...gle.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 Thu, Apr 18, 2024 at 5:23 AM Jason Xing <kerneljasonxing@...il.com> wrote:
>
> On Thu, Apr 18, 2024 at 12:59 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>
>
> Reviewed-by: Jason Xing <kerneljasonxing@...il.com>
>
> I wonder if we're supposed to move this check into ip_icmp_error()
> like ipv6_icmp_error() does, because I notice one caller
> rxrpc_encap_err_rcv() without checking RECVERR  bit reuses the ICMP
> error logic which is introduced in commit b6c66c4324e7 ("rxrpc: Use
> the core ICMP/ICMP6 parsers'')?

I tried to focus on the TCP issues, and to have a stable candidate for patch #1.

The refactoring can wait.

>
> Or should it be a follow-up patch (moving it inside of
> ip_icmp_error()) to handle the rxrpc case and also prevent future
> misuse for other people?