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

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Message-Id: <20180510.174908.2166045029697003189.davem@davemloft.net>
Date:   Thu, 10 May 2018 17:49:08 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     lucien.xin@...il.com
Cc:     netdev@...r.kernel.org, linux-sctp@...r.kernel.org,
        marcelo.leitner@...il.com, nhorman@...driver.com,
        syzkaller@...glegroups.com
Subject: Re: [PATCH net] sctp: remove sctp_chunk_put from fail_mark err
 path in sctp_ulpevent_make_rcvmsg

From: Xin Long <lucien.xin@...il.com>
Date: Thu, 10 May 2018 17:34:13 +0800

> 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>

Applied and queued up for -stable.