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

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Message-ID: <CANn89iLSZFOYfZUSK57LLe8yw4wNt8vHt=aD79a1MbZBhfeRbw@mail.gmail.com>
Date: Thu, 18 Apr 2024 11:26:33 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Paolo Abeni <pabeni@...hat.com>, David Ahern <dsahern@...nel.org>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 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 10:03 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Thu, Apr 18, 2024 at 10:02 AM Paolo Abeni <pabeni@...hat.com> wrote:
> >
> > Hi,
> >
> > On Wed, 2024-04-17 at 16:57 +0000, Eric Dumazet 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);
> >
> > We have a fcnal-test.sh self-test failure:
> >
> > https://netdev.bots.linux.dev/contest.html?branch=net-next-2024-04-18--06-00&test=fcnal-test-sh
> >
> > that I suspect are related to this patch (or the following one): the
> > test case creates a TCP connection on loopback and this is the only
> > patchseries touching the related code, included in the relevant patch
> > burst.
> >
> > Could you please have a look?
>
> Sure, thanks Paolo !

First patch is fine, I see no failure from fcnal-test.sh (as I would expect)

For the second one, I am not familiar enough with this very slow test
suite (all these "sleep 1" ... oh well)

I guess "failing tests" depended on TCP connect() to immediately abort
on one ICMP message,
depending on old kernel behavior.

I do not know how to launch a subset of the tests, and trace these.

"./fcnal-test.sh -t ipv4_tcp" alone takes more than 9 minutes [1] in a
VM running a non debug kernel :/

David, do you have an idea how to proceed ?

Thanks.

[1]
Tests passed: 134
Tests failed:   0

real 9m33.085s
user 0m40.159s
sys 0m30.098s