netdev - Re: [PATCH net] sctp: remove sctp_chunk_put from fail_mark err path in sctp_ulpevent_make

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Message-ID: <20180510115821.GA4898@hmswarspite.think-freely.org>
Date:   Thu, 10 May 2018 07:58:21 -0400
From:   Neil Horman <nhorman@...driver.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org,
        davem@...emloft.net,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        syzkaller@...glegroups.com
Subject: Re: [PATCH net] sctp: remove sctp_chunk_put from fail_mark err path
 in sctp_ulpevent_make_rcvmsg

On Thu, May 10, 2018 at 05:34:13PM +0800, Xin Long wrote:
> In Commit 1f45f78f8e51 ("sctp: allow GSO frags to access the chunk too"),
> it held the chunk in sctp_ulpevent_make_rcvmsg to access it safely later
> in recvmsg. However, it also added sctp_chunk_put in fail_mark err path,
> which is only triggered before holding the chunk.
> 
> syzbot reported a use-after-free crash happened on this err path, where
> it shouldn't call sctp_chunk_put.
> 
> This patch simply removes this call.
> 
> Fixes: 1f45f78f8e51 ("sctp: allow GSO frags to access the chunk too")
> Reported-by: syzbot+141d898c5f24489db4aa@...kaller.appspotmail.com
> Signed-off-by: Xin Long <lucien.xin@...il.com>
> ---
>  net/sctp/ulpevent.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/net/sctp/ulpevent.c b/net/sctp/ulpevent.c
> index 84207ad..8cb7d98 100644
> --- a/net/sctp/ulpevent.c
> +++ b/net/sctp/ulpevent.c
> @@ -715,7 +715,6 @@ struct sctp_ulpevent *sctp_ulpevent_make_rcvmsg(struct sctp_association *asoc,
>  	return event;
>  
>  fail_mark:
> -	sctp_chunk_put(chunk);
>  	kfree_skb(skb);
>  fail:
>  	return NULL;
> -- 
> 2.1.0
> 
> 
Acked-by: Neil Horman <nhorman@...driver.com>