[net] sctp: avoid BUG_ON on sctp_wait_for_sndbuf

Alexander Popov reported that an application may trigger a BUG_ON in
sctp_wait_for_sndbuf if the socket tx buffer is full, a thread is
waiting on it to queue more data and meanwhile another thread peels off
the association being used by the first thread.

This patch replaces the BUG_ON call with a proper error handling. It
will return -EPIPE to the original sendmsg call, similarly to what would
have been done if the association wasn't found in the first place.

Acked-by: Alexander Popov <alex.popov@linux.com>
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
---
Please consider this to -stable. Thanks

 net/sctp/socket.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

On Tue, Feb 7, 2017 at 4:10 AM, Marcelo Ricardo Leitner
<marcelo.leitner@gmail.com> wrote:
> Alexander Popov reported that an application may trigger a BUG_ON in
> sctp_wait_for_sndbuf if the socket tx buffer is full, a thread is
> waiting on it to queue more data and meanwhile another thread peels off
> the association being used by the first thread.
>
> This patch replaces the BUG_ON call with a proper error handling. It
> will return -EPIPE to the original sendmsg call, similarly to what would
> have been done if the association wasn't found in the first place.
>
> Acked-by: Alexander Popov <alex.popov@linux.com>
> Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
> ---
> Please consider this to -stable. Thanks
>
Reviewed-by: Xin Long <lucien.xin@gmail.com>

>  net/sctp/socket.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> index 37eeab7899fc235a56bd2f4ccdb3e6c338a8d48e..e214d2e7e9a30c02847daf354668c42eeaffd0d6 100644
> --- a/net/sctp/socket.c
> +++ b/net/sctp/socket.c
> @@ -7426,7 +7426,8 @@ static int sctp_wait_for_sndbuf(struct sctp_association *asoc, long *timeo_p,
>                  */
>                 release_sock(sk);
>                 current_timeo = schedule_timeout(current_timeo);
> -               BUG_ON(sk != asoc->base.sk);
> +               if (sk != asoc->base.sk)
> +                       goto do_error;
>                 lock_sock(sk);
>
>                 *timeo_p = current_timeo;
> --
> 2.9.3
>
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From: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Date: Mon,  6 Feb 2017 18:10:31 -0200

> Alexander Popov reported that an application may trigger a BUG_ON in
> sctp_wait_for_sndbuf if the socket tx buffer is full, a thread is
> waiting on it to queue more data and meanwhile another thread peels off
> the association being used by the first thread.
> 
> This patch replaces the BUG_ON call with a proper error handling. It
> will return -EPIPE to the original sendmsg call, similarly to what would
> have been done if the association wasn't found in the first place.
> 
> Acked-by: Alexander Popov <alex.popov@linux.com>
> Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
> ---
> Please consider this to -stable. Thanks

Applied and queued up for -stable, thanks a lot.