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Date:   Tue, 27 Sep 2022 09:48:24 -0700
From:   Kuniyuki Iwashima <kuniyu@...zon.com>
To:     <edumazet@...gle.com>
CC:     <davem@...emloft.net>, <dsahern@...nel.org>, <kuba@...nel.org>,
        <kuni1840@...il.com>, <kuniyu@...zon.com>,
        <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
        <pabeni@...hat.com>, <syzkaller-bugs@...glegroups.com>
Subject: Re: [PATCH v1 net 5/5] tcp: Fix data races around icsk->icsk_af_ops.

From:   Eric Dumazet <edumazet@...gle.com>
Date:   Tue, 27 Sep 2022 09:39:37 -0700
> On Tue, Sep 27, 2022 at 9:33 AM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
> >
> > IPV6_ADDRFORM changes icsk->icsk_af_ops under lock_sock(), but
> > tcp_(get|set)sockopt() read it locklessly.  To avoid load/store
> > tearing, we need to add READ_ONCE() and WRITE_ONCE() for the reads
> > and write.
> 
> I am pretty sure I have released a syzkaller bug recently with this issue.
> Have you seen this?
> If yes, please include the appropriate syzbot tag.

No, I haven't.
Could you provide the URL?
I'm happy to include the syzbot tag and KCSAN report in the changelog.


> > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
> > ---
> >  net/ipv4/tcp.c           | 10 ++++++----
> >  net/ipv6/ipv6_sockglue.c |  3 ++-
> >  2 files changed, 8 insertions(+), 5 deletions(-)
> >
> > diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> > index e373dde1f46f..c86dd0ccef5b 100644
> > --- a/net/ipv4/tcp.c
> > +++ b/net/ipv4/tcp.c
> > @@ -3795,8 +3795,9 @@ int tcp_setsockopt(struct sock *sk, int level, int optname, sockptr_t optval,
> >         const struct inet_connection_sock *icsk = inet_csk(sk);
> >
> >         if (level != SOL_TCP)
> > -               return icsk->icsk_af_ops->setsockopt(sk, level, optname,
> > -                                                    optval, optlen);
> > +               /* IPV6_ADDRFORM can change icsk->icsk_af_ops under us. */
> > +               return READ_ONCE(icsk->icsk_af_ops)->setsockopt(sk, level, optname,
> > +                                                               optval, optlen);
> >         return do_tcp_setsockopt(sk, level, optname, optval, optlen);
> >  }
> >  EXPORT_SYMBOL(tcp_setsockopt);
> > @@ -4394,8 +4395,9 @@ int tcp_getsockopt(struct sock *sk, int level, int optname, char __user *optval,
> >         struct inet_connection_sock *icsk = inet_csk(sk);
> >
> >         if (level != SOL_TCP)
> > -               return icsk->icsk_af_ops->getsockopt(sk, level, optname,
> > -                                                    optval, optlen);
> > +               /* IPV6_ADDRFORM can change icsk->icsk_af_ops under us. */
> > +               return READ_ONCE(icsk->icsk_af_ops)->getsockopt(sk, level, optname,
> > +                                                               optval, optlen);
> >         return do_tcp_getsockopt(sk, level, optname, optval, optlen);
> >  }
> >  EXPORT_SYMBOL(tcp_getsockopt);
> > diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
> > index a89db5872dc3..726d95859898 100644
> > --- a/net/ipv6/ipv6_sockglue.c
> > +++ b/net/ipv6/ipv6_sockglue.c
> > @@ -479,7 +479,8 @@ static int do_ipv6_setsockopt(struct sock *sk, int level, int optname,
> >
> >                                 /* Paired with READ_ONCE(sk->sk_prot) in inet6_stream_ops */
> >                                 WRITE_ONCE(sk->sk_prot, &tcp_prot);
> > -                               icsk->icsk_af_ops = &ipv4_specific;
> > +                               /* Paired with READ_ONCE() in tcp_(get|set)sockopt() */
> > +                               WRITE_ONCE(icsk->icsk_af_ops, &ipv4_specific);
> >                                 sk->sk_socket->ops = &inet_stream_ops;
> >                                 sk->sk_family = PF_INET;
> >                                 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
> > --
> > 2.30.2
> >

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