From mboxrd@z Thu Jan  1 00:00:00 1970
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From: Christoph Paasch <cpaasch at apple.com>
To: mptcp at lists.01.org
Subject: [MPTCP] Re: [PATCH net] mptcp: fix NULL ptr dereference in MP_JOIN
 error path
Date: Thu, 28 May 2020 08:42:16 -0700
Message-ID: <20200528154216.GC64606@MacBook-Pro-64.local>
In-Reply-To: 9647c930082b73112fcd9e4688d6609d36f47443.camel@redhat.com
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On 05/28/20 - 15:35, Paolo Abeni wrote:
> On Thu, 2020-05-28 at 15:27 +0200, Paolo Abeni wrote:
> > When token lookup on MP_JOIN 3rd ack fails, the server
> > socket closes with a reset the incoming child. Such socket
> > has the 'is_mptcp' flag set, but no msk socket associated
> > - due to the failed lookup.
> > =

> > While crafting the reset packet mptcp_established_options_mp()
> > will try to dereference the child's master socket, causing
> > a NULL ptr dereference.
> > =

> > This change addresses the issue with explicit fallback to
> > TCP in such error path.
> > =

> > Fixes: f296234c98a8 ("mptcp: Add handling of incoming MP_JOIN requests")
> > Signed-off-by: Paolo Abeni <pabeni(a)redhat.com>
> > ---
> >  net/mptcp/subflow.c | 17 +++++++++++++----
> >  net/mptcp/token.c   | 10 +++++++---
> >  2 files changed, 20 insertions(+), 7 deletions(-)
> > =

> > diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
> > index ae7bcdb7f990..55fced4f136d 100644
> > --- a/net/mptcp/subflow.c
> > +++ b/net/mptcp/subflow.c
> > @@ -408,6 +408,17 @@ static void subflow_ulp_fallback(struct sock *sk,
> >  	tcp_sk(sk)->is_mptcp =3D 0;
> >  }
> >  =

> > +static void subflow_drop_ctx(struct sock *ssk)
> > +{
> > +	struct mptcp_subflow_context *ctx =3D mptcp_subflow_ctx(ssk);
> > +
> > +	if (!ctx)
> > +		return;
> > +
> > +	subflow_ulp_fallback(ssk, ctx);
> > +	kfree_rcu(ctx, rcu);
> > +}
> > +
> >  static struct sock *subflow_syn_recv_sock(const struct sock *sk,
> >  					  struct sk_buff *skb,
> >  					  struct request_sock *req,
> > @@ -480,10 +491,7 @@ static struct sock *subflow_syn_recv_sock(const st=
ruct sock *sk,
> >  			if (fallback_is_fatal)
> >  				goto dispose_child;
> >  =

> > -			if (ctx) {
> > -				subflow_ulp_fallback(child, ctx);
> > -				kfree_rcu(ctx, rcu);
> > -			}
> > +			subflow_drop_ctx(child);
> >  			goto out;
> >  		}
> >  =

> > @@ -532,6 +540,7 @@ static struct sock *subflow_syn_recv_sock(const str=
uct sock *sk,
> >  	return child;
> >  =

> >  dispose_child:
> > +	subflow_drop_ctx(child);
> >  	tcp_rsk(req)->drop_req =3D true;
> >  	tcp_send_active_reset(child, GFP_ATOMIC);
> >  	inet_csk_prepare_for_destroy_sock(child);
> > diff --git a/net/mptcp/token.c b/net/mptcp/token.c
> > index c0327ff5d1b7..d1068b51a45a 100644
> > --- a/net/mptcp/token.c
> > +++ b/net/mptcp/token.c
> > @@ -216,16 +216,20 @@ struct mptcp_sock *mptcp_token_get_sock(u32 token)
> >  		msk =3D mptcp_sk(sk);
> >  		if (READ_ONCE(msk->token) !=3D token)
> >  			continue;
> > -		if (!refcount_inc_not_zero(&sk->sk_refcnt))
> > +		if (!refcount_inc_not_zero(&sk->sk_refcnt)) {
> > +			pr_warn("token match %x but 0 rfcnt\n", token);
> >  			goto not_found;
> > -		if (READ_ONCE(msk->token) !=3D token) {
> > +		} if (READ_ONCE(msk->token) !=3D token) {
> > +			pr_warn("token mis-match %x:%x after get\n", READ_ONCE(msk->token),=
 token);
> >  			sock_put(sk);
> >  			goto again;
> >  		}
> >  		goto found;
> >  	}
> > -	if (get_nulls_value(pos) !=3D (token & token_mask))
> > +	if (get_nulls_value(pos) !=3D (token & token_mask)) {
> > +		pr_warn("moved nulls %ld id %d\n", get_nulls_value(pos), token & tok=
en_mask);
> >  		goto again;
> > +	}
> >  =

> >  not_found:
> >  	msk =3D NULL;
> =

> whoops, I rushed too much and included also unneeded dbg. will send a
> v2 later.
> =

> Sorry for the noise,

And I didn't read this email here before reading your other one ;-)

Sorry for the noise as well!


Christoph

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