Re: [PATCH net] sctp: fix error path in sctp_stream_init

[Neil Horman <nhorman@tuxdriver.com>]

On Tue, Jan 02, 2018 at 07:44:37PM -0200, Marcelo Ricardo Leitner wrote:
> syzbot noticed a NULL pointer dereference panic in sctp_stream_free()
> which was caused by an incomplete error handling in sctp_stream_init().
> By not clearing stream->outcnt, it made a for() in sctp_stream_free()
> think that it had elements to free, but not, leading to the panic.
> 
> As suggested by Xin Long, this patch also simplifies the error path by
> moving it to the only if() that uses it.
> 
> See-also: https://www.spinics.net/lists/netdev/msg473756.html
> See-also: https://www.spinics.net/lists/netdev/msg465024.html
> Reported-by: syzbot <syzkaller@googlegroups.com>
> Fixes: f952be79cebd ("sctp: introduce struct sctp_stream_out_ext")
> Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
> ---
>  net/sctp/stream.c | 22 ++++++++++------------
>  1 file changed, 10 insertions(+), 12 deletions(-)
> 
> diff --git a/net/sctp/stream.c b/net/sctp/stream.c
> index 76ea66be0bbee7d3f018676d52c8b95ba06dbcb1..524dfeb94c41ab1ac735746a8acf93af1c96ae48 100644
> --- a/net/sctp/stream.c
> +++ b/net/sctp/stream.c
> @@ -156,9 +156,9 @@ int sctp_stream_init(struct sctp_stream *stream, __u16 outcnt, __u16 incnt,
>  	sctp_stream_outq_migrate(stream, NULL, outcnt);
>  	sched->sched_all(stream);
>  
> -	i = sctp_stream_alloc_out(stream, outcnt, gfp);
> -	if (i)
> -		return i;
> +	ret = sctp_stream_alloc_out(stream, outcnt, gfp);
> +	if (ret)
> +		goto out;
>  
>  	stream->outcnt = outcnt;
>  	for (i = 0; i < stream->outcnt; i++)
> @@ -170,19 +170,17 @@ int sctp_stream_init(struct sctp_stream *stream, __u16 outcnt, __u16 incnt,
>  	if (!incnt)
>  		goto out;
>  
> -	i = sctp_stream_alloc_in(stream, incnt, gfp);
> -	if (i) {
> -		ret = -ENOMEM;
> -		goto free;
> +	ret = sctp_stream_alloc_in(stream, incnt, gfp);
> +	if (ret) {
> +		sched->free(stream);
> +		kfree(stream->out);
> +		stream->out = NULL;
> +		stream->outcnt = 0;
> +		goto out;
>  	}
>  
>  	stream->incnt = incnt;
> -	goto out;
>  
> -free:
> -	sched->free(stream);
> -	kfree(stream->out);
> -	stream->out = NULL;
>  out:
>  	return ret;
>  }
> -- 
> 2.14.3
> 
> 
Acked-by: Neil Horman <nhorman@tuxdriver.com>