netdev - Re: [PATCH net] sctp: fix err handling of stream initialization

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Date:   Mon, 23 Dec 2019 07:46:09 -0500
From:   Neil Horman <nhorman@...driver.com>
To:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc:     netdev@...r.kernel.org, linux-sctp@...r.kernel.org,
        Xin Long <lucien.xin@...il.com>,
        syzbot <syzbot+9a1bc632e78a1a98488b@...kaller.appspotmail.com>,
        syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH net] sctp: fix err handling of stream initialization

On Fri, Dec 20, 2019 at 03:03:44PM -0300, Marcelo Ricardo Leitner wrote:
> The fix on 951c6db954a1 fixed the issued reported there but introduced
> another. When the allocation fails within sctp_stream_init() it is
> okay/necessary to free the genradix. But it is also called when adding
> new streams, from sctp_send_add_streams() and
> sctp_process_strreset_addstrm_in() and in those situations it cannot
> just free the genradix because by then it is a fully operational
> association.
> 
> The fix here then is to only free the genradix in sctp_stream_init()
> and on those other call sites  move on with what it already had and let
> the subsequent error handling to handle it.
> 
> Tested with the reproducers from this report and the previous one,
> with lksctp-tools and sctp-tests.
> 
> Reported-by: syzbot+9a1bc632e78a1a98488b@...kaller.appspotmail.com
> Fixes: 951c6db954a1 ("sctp: fix memleak on err handling of stream initialization")
> Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
> ---
>  net/sctp/stream.c | 30 +++++++++++++++---------------
>  1 file changed, 15 insertions(+), 15 deletions(-)
> 
> diff --git a/net/sctp/stream.c b/net/sctp/stream.c
> index 6a30392068a04bfcefcb14c3d7f13fc092d59cd3..c1a100d2fed39c2d831487e05fcbf5e8d507d470 100644
> --- a/net/sctp/stream.c
> +++ b/net/sctp/stream.c
> @@ -84,10 +84,8 @@ static int sctp_stream_alloc_out(struct sctp_stream *stream, __u16 outcnt,
>  		return 0;
>  
>  	ret = genradix_prealloc(&stream->out, outcnt, gfp);
> -	if (ret) {
> -		genradix_free(&stream->out);
> +	if (ret)
>  		return ret;
> -	}
>  
>  	stream->outcnt = outcnt;
>  	return 0;
> @@ -102,10 +100,8 @@ static int sctp_stream_alloc_in(struct sctp_stream *stream, __u16 incnt,
>  		return 0;
>  
>  	ret = genradix_prealloc(&stream->in, incnt, gfp);
> -	if (ret) {
> -		genradix_free(&stream->in);
> +	if (ret)
>  		return ret;
> -	}
>  
>  	stream->incnt = incnt;
>  	return 0;
> @@ -123,7 +119,7 @@ int sctp_stream_init(struct sctp_stream *stream, __u16 outcnt, __u16 incnt,
>  	 * a new one with new outcnt to save memory if needed.
>  	 */
>  	if (outcnt == stream->outcnt)
> -		goto in;
> +		goto handle_in;
>  
>  	/* Filter out chunks queued on streams that won't exist anymore */
>  	sched->unsched_all(stream);
> @@ -132,24 +128,28 @@ int sctp_stream_init(struct sctp_stream *stream, __u16 outcnt, __u16 incnt,
>  
>  	ret = sctp_stream_alloc_out(stream, outcnt, gfp);
>  	if (ret)
> -		goto out;
> +		goto out_err;
>  
>  	for (i = 0; i < stream->outcnt; i++)
>  		SCTP_SO(stream, i)->state = SCTP_STREAM_OPEN;
>  
> -in:
> +handle_in:
>  	sctp_stream_interleave_init(stream);
>  	if (!incnt)
>  		goto out;
>  
>  	ret = sctp_stream_alloc_in(stream, incnt, gfp);
> -	if (ret) {
> -		sched->free(stream);
> -		genradix_free(&stream->out);
> -		stream->outcnt = 0;
> -		goto out;
> -	}
> +	if (ret)
> +		goto in_err;
> +
> +	goto out;
>  
> +in_err:
> +	sched->free(stream);
> +	genradix_free(&stream->in);
> +out_err:
> +	genradix_free(&stream->out);
Isn't this effectively a double free in the fall through case?
Neil

> +	stream->outcnt = 0;
>  out:
>  	return ret;
>  }
> -- 
> 2.23.0
> 
>