netdev - Re: [PATCH v2] sctp: Fix double free in sctp_sendmsg_to

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Date:   Thu, 15 Mar 2018 14:32:46 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     nhorman@...driver.com
Cc:     linux-sctp@...r.kernel.org, netdev@...r.kernel.org,
        lucien.xin@...il.com
Subject: Re: [PATCH v2] sctp: Fix double free in sctp_sendmsg_to_asoc

From: Neil Horman <nhorman@...driver.com>
Date: Mon, 12 Mar 2018 14:15:25 -0400

> syzbot/kasan detected a double free in sctp_sendmsg_to_asoc:
> BUG: KASAN: use-after-free in sctp_association_free+0x7b7/0x930
> net/sctp/associola.c:332
> Read of size 8 at addr ffff8801d8006ae0 by task syzkaller914861/4202
 ...
> This was introduced by commit:
> f84af33 sctp: factor out sctp_sendmsg_to_asoc from sctp_sendmsg
> 
> As the newly refactored function moved the wait_for_sndbuf call to a
> point after the association was connected, allowing for peeloff events
> to occur, which in turn caused wait_for_sndbuf to return -EPIPE which
> was not caught by the logic that determines if an association should be
> freed or not.
> 
> Fix it the easy way by returning the ordering of
> sctp_primitive_ASSOCIATE and sctp_wait_for_sndbuf to the old order, to
> ensure that EPIPE will not happen.
> 
> Tested by myself using the syzbot reproducers with positive results
> 
> Signed-off-by: Neil Horman <nhorman@...driver.com>
> CC: davem@...emloft.net
> CC: Xin Long <lucien.xin@...il.com>
> Reported-by: syzbot+a4e4112c3aff00c8cfd8@...kaller.appspotmail.com

Applied, thanks Neil.