From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2B4EE1514D8; Wed, 27 Mar 2024 19:10:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711566630; cv=none; b=LXXx+7W+MQWfJ5hR0BJGoFED3RMWG8zPlQsqaD29GSjRVeUx10SEUHEO3oLegEvr51rk3BpAYaNsOaFdzbhI77I93JTXx8isPS3dUlPtQ6TSUAcxl6wDSdbve8RS0DX0u1pcuGqawZMpIAnnSuXzPWweU1NqGg3kHpArcOALV/w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711566630; c=relaxed/simple; bh=ceAJBDJsMQ5sDuySRq7ldhrporPZTG7ZT1EpQXcXN1Y=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=lUuu6kmhDEGaFrv1j7M/uNnetq0P7KqBD9lXaB60xim4dnDcr0RJt5WCV1TKZAtM+wOmfGTq05/aLBFG1PvtDEearaGIUbbdl9FKyuVeftAeqN9wOvZQPcQYGyqVL61+C5iX2aoHdf7wgrYfTKDrdn7SQbCeCmgwEky7Rbcqpj4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=R1Q1iO77; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="R1Q1iO77" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D33E7C433F1; Wed, 27 Mar 2024 19:10:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1711566629; bh=ceAJBDJsMQ5sDuySRq7ldhrporPZTG7ZT1EpQXcXN1Y=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=R1Q1iO770PoO1j4FciX9Y5BU9kmYJujFc52pzkyG+BLJxx/CLBKAAVYC8Lt9REJDJ HpckABPRRQMoSyMxYM0p1Dv4Qi8flAq+1UXQhAVh5rKC0QHADZxp9GwXbp8IWoXTQA 5f4/qnMydLfKJ3dMCIj2cgBUYE+CCuyNkB6AAhB8jv9Xd+ZdjqaK7hpormBBPSP+In wFrgpYsxVFyY48Va7RwjLqmZ/hgQOQEg+gLxCgg6+PtJ4mTvxXMXP214XILZM0HdyS sZy3JhkjTuROHpTWwwtLu11nXHKCWNHvX73CzzQyec4rdFXxAlZY4Jj2ea28lIrr+a l4JTADtsvGHyw== Date: Wed, 27 Mar 2024 19:10:25 +0000 From: Simon Horman To: Duoming Zhou Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-hams@vger.kernel.org, pabeni@redhat.com, kuba@kernel.org, edumazet@google.com, davem@davemloft.net, jreuter@yaina.de Subject: Re: [PATCH net] ax25: fix use-after-free bugs caused by ax25_ds_del_timer Message-ID: <20240327191025.GU403975@kernel.org> References: <20240326142542.118058-1-duoming@zju.edu.cn> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240326142542.118058-1-duoming@zju.edu.cn> On Tue, Mar 26, 2024 at 10:25:42PM +0800, Duoming Zhou wrote: > When the ax25 device is detaching, the ax25_dev_device_down() > calls ax25_ds_del_timer() to cleanup the slave_timer. When > the timer handler is running, the ax25_ds_del_timer() that > calls del_timer() in it will return directly. As a result, > the use-after-free bugs could happen, one of the scenarios > is shown below: > > (Thread 1) | (Thread 2) > | ax25_ds_timeout() > ax25_dev_device_down() | > ax25_ds_del_timer() | > del_timer() | > ax25_dev_put() //FREE | > | ax25_dev-> //USE > > In order to mitigate bugs, when the device is detaching, use > timer_shutdown_sync() to stop the timer. FWIIW, in my reading of things there is another failure mode whereby ax25_ds_timeout may rearm the timer after the call to del_timer() but before the call to ax25_dev_put(). > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > Signed-off-by: Duoming Zhou > --- > net/ax25/ax25_ds_timer.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/net/ax25/ax25_ds_timer.c b/net/ax25/ax25_ds_timer.c > index c4f8adbf814..5624c0d174c 100644 > --- a/net/ax25/ax25_ds_timer.c > +++ b/net/ax25/ax25_ds_timer.c > @@ -43,7 +43,12 @@ void ax25_ds_setup_timer(ax25_dev *ax25_dev) > > void ax25_ds_del_timer(ax25_dev *ax25_dev) > { > - if (ax25_dev) > + if (!ax25_dev) > + return; > + > + if (!ax25_dev->device_up) > + timer_shutdown_sync(&ax25_dev->dama.slave_timer); > + else > del_timer(&ax25_dev->dama.slave_timer); > } I think that a) it is always correct to call timer_shutdown_sync, and b) ax25_dev->device_up is always true. So a call to timer_shutdown_sync can simply replace the call to del_timer. Also, not strictly related, I think ax25_dev cannot be NULL, so that check could be dropped. But perhaps that is better left alone. Zooming out a bit, has removal of ax25 been considered. I didn't check the logs thoroughly, but I'm not convinced it's been maintained - other than clean-ups and by-inspection bug fixes - since git history began.