netdev - Re: [PATCH net] sctp: set sk_state back to CLOSED if autobind fails in sctp_listen

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Message-ID: <CADvbK_cPTb6YgmSvh=3TpNyYzkZLGP8dv95dHKD5JwpvjxUQhg@mail.gmail.com>
Date: Tue, 1 Oct 2024 15:41:23 -0400
From: Xin Long <lucien.xin@...il.com>
To: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc: network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org, davem@...emloft.net, 
	kuba@...nel.org, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net] sctp: set sk_state back to CLOSED if autobind fails
 in sctp_listen_start

On Tue, Oct 1, 2024 at 3:15 PM Marcelo Ricardo Leitner
<marcelo.leitner@...il.com> wrote:
>
> On Mon, Sep 30, 2024 at 04:49:51PM -0400, Xin Long wrote:
> > In sctp_listen_start() invoked by sctp_inet_listen(), it should set the
> > sk_state back to CLOSED if sctp_autobind() fails due to whatever reason.
> >
> > Otherwise, next time when calling sctp_inet_listen(), if sctp_sk(sk)->reuse
> > is already set via setsockopt(SCTP_REUSE_PORT), sctp_sk(sk)->bind_hash will
> > be dereferenced as sk_state is LISTENING, which causes a crash as bind_hash
> > is NULL.
> >
> >   KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
> >   RIP: 0010:sctp_inet_listen+0x7f0/0xa20 net/sctp/socket.c:8617
> >   Call Trace:
> >    <TASK>
> >    __sys_listen_socket net/socket.c:1883 [inline]
> >    __sys_listen+0x1b7/0x230 net/socket.c:1894
> >    __do_sys_listen net/socket.c:1902 [inline]
> >
> > Fixes: 5e8f3f703ae4 ("sctp: simplify sctp listening code")
> > Reported-by: syzbot+f4e0f821e3a3b7cee51d@...kaller.appspotmail.com
> > Signed-off-by: Xin Long <lucien.xin@...il.com>
> > ---
> >  net/sctp/socket.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> > index 32f76f1298da..078bcb3858c7 100644
> > --- a/net/sctp/socket.c
> > +++ b/net/sctp/socket.c
> > @@ -8557,8 +8557,10 @@ static int sctp_listen_start(struct sock *sk, int backlog)
> >        */
> >       inet_sk_set_state(sk, SCTP_SS_LISTENING);
> >       if (!ep->base.bind_addr.port) {
> > -             if (sctp_autobind(sk))
> > +             if (sctp_autobind(sk)) {
> > +                     inet_sk_set_state(sk, SCTP_SS_CLOSED);
> >                       return -EAGAIN;
> > +             }
> >       } else {
> >               if (sctp_get_port(sk, inet_sk(sk)->inet_num)) {
> >                       inet_sk_set_state(sk, SCTP_SS_CLOSED);
>
> Then AFAICT the end of the function needs a patch as well, because it
> returns what could be an error directly, without undoing this:
>
>         WRITE_ONCE(sk->sk_max_ack_backlog, backlog);
>         return sctp_hash_endpoint(ep);
> }
>
Right, but this is another issue and won't cause a crash, and the fix will
need a different "Fixes:". I think we should fix it in a separate patch.