netdev - Re: [Patch net] smc: disallow TCP_ULP in smc

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Date:   Mon, 12 Apr 2021 12:09:10 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Karsten Graul <kgraul@...ux.ibm.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        linux-s390@...r.kernel.org, Cong Wang <cong.wang@...edance.com>,
        syzbot <syzbot+b54a1ce86ba4a623b7f0@...kaller.appspotmail.com>,
        John Fastabend <john.fastabend@...il.com>
Subject: Re: [Patch net] smc: disallow TCP_ULP in smc_setsockopt()

On Sun, Apr 11, 2021 at 11:52 PM Karsten Graul <kgraul@...ux.ibm.com> wrote:
>
>
>
> On 10/04/2021 20:17, Cong Wang wrote:
> > From: Cong Wang <cong.wang@...edance.com>
> >
> > syzbot is able to setup kTLS on an SMC socket, which coincidentally
> > uses sk_user_data too, later, kTLS treats it as psock so triggers a
> > refcnt warning. The cause is that smc_setsockopt() simply calls
> > TCP setsockopt(). I do not think it makes sense to setup kTLS on
> > top of SMC, so we can just disallow this.
> >
> > Reported-and-tested-by: syzbot+b54a1ce86ba4a623b7f0@...kaller.appspotmail.com
> > Cc: John Fastabend <john.fastabend@...il.com>
> > Cc: Karsten Graul <kgraul@...ux.ibm.com>
> > Signed-off-by: Cong Wang <cong.wang@...edance.com>
> > ---
> >  net/smc/af_smc.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
> > index 47340b3b514f..0d4d6d28f20c 100644
> > --- a/net/smc/af_smc.c
> > +++ b/net/smc/af_smc.c
> > @@ -2162,6 +2162,9 @@ static int smc_setsockopt(struct socket *sock, int level, int optname,
> >       struct smc_sock *smc;
> >       int val, rc;
> >
> > +     if (optname == TCP_ULP)
> > +             return -EOPNOTSUPP;
> > +
> >       smc = smc_sk(sk);
> >
> >       /* generic setsockopts reaching us here always apply to the
> > @@ -2186,7 +2189,6 @@ static int smc_setsockopt(struct socket *sock, int level, int optname,
> >       if (rc || smc->use_fallback)
> >               goto out;
> >       switch (optname) {
> > -     case TCP_ULP:
>
> Should'nt it return -EOPNOTSUPP in that case, too?

I do not think I understand this. In case of TCP_ULP, we will
not even reach this switch case after my patch.

Thanks.