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

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Message-ID: <ZvxKVpfDhuYIyXll@t14s.localdomain>
Date: Tue, 1 Oct 2024 16:15:34 -0300
From: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To: Xin Long <lucien.xin@...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 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);
}