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 5DC9716D329; Wed, 24 Apr 2024 18:13:38 +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=1713982418; cv=none; b=SinPG01Z0Ebjra2DDAwP3ipOoMCLr+Y5IqekZsYUEHmsBb60AZO2IqH158zqezmrtJAqOc+TyJ/JdobMMVuSyVk4x+/iKALpqjzO57TkwZtDBSQr2otceoejV2pDf/7H7OKYwDlFRkiR2F4yLoPqflOpx8O47JfJz4iQSmr3404= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713982418; c=relaxed/simple; bh=81/fj7NjD+zEcRV5jk9TtHGDgfY372bpY0fjY6dUMzE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=JshbuZhOezV6cYTpSHyAm4baop7KOzbpxe55t4Dzd9oyqOtmnjdtQiomxWEo+0HgtvSqoOolJQF4ZOseCtZzzH4whbkKp7c2z0oAOB1suxtEr1OOvt+vtEUERwFkfJAVin3rut6f+xWTaJINiXwUFfkWz0QbXuY2xlYuBYLXIZI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=cJYNSFF/; 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="cJYNSFF/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B371BC113CD; Wed, 24 Apr 2024 18:13:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1713982417; bh=81/fj7NjD+zEcRV5jk9TtHGDgfY372bpY0fjY6dUMzE=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=cJYNSFF/BQfBxPV0nolpfeWaxorLN5m7KP81JBIPoFpCmnFlQzLnLIyCGw418QS8X xGyREA6XP697XH5DM0tJtxpZBf2DlE/BM/YyQunhzZu6HrfTXpsZZQj5jzL7Y50gso 8cEK5NJfCLmNLFbEE/GR0a3pmBixj7t4LgJpFOnCH+OMgIfEAumIBrA+LU10P7R0R9 SegMtR69zN5sgRn6wU7Ig/XlEe9RFMw1CH+i+ORJv9ZQpkQqSrxQOX+ZTnPXxvFD0q EVQ8O/J3qjb5TmHZYA95Fmznb9zwdsUCzpHcPM1bCQYmfMVVnGYclGuKRGbHS+wacB yf452MPkLMdxA== Message-ID: <8a01c6b2-ca30-448c-8ba8-34720891b461@kernel.org> Date: Wed, 24 Apr 2024 20:13:31 +0200 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] nfc: pn533: Fix null-ptr-deref in pn533_recv_frame() To: Yuxuan-Hu , Yuxuan Hu <20373622@buaa.edu.cn>, gregkh@linuxfoundation.org, johan@kernel.org, davem@davemloft.net, u.kleine-koenig@pengutronix.de, Jonathan.Cameron@huawei.com, francesco.dolcini@toradex.com, jirislaby@kernel.org Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, baijiaju1990@gmail.com, sy2239101@buaa.edu.cn References: From: Krzysztof Kozlowski Content-Language: en-US Autocrypt: addr=krzk@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 24/04/2024 16:00, Yuxuan-Hu wrote: > Hi Krzysztof, > Thanks for your reply. > > On 2024/4/24 13:36, Krzysztof Kozlowski wrote: >> A bit better solution would be to NULL-ify dev->cmd at the beginning of >> pn533_send_async_complete(), because that seems logical. The complete >> callback takes ownership of dev->cmd, so why it performs the assignment >> at the end? >> >> However even above code will keep the race open for short period. >> Probably some locking would solve it or checking for dev->cmd in few >> places with barriers. >> >> Best regards, >> Krzysztof > > I think adding a lock seems to be a better solution, however, acquire a > lock on each access to dev->cmd does not seem to be an appropriate > implementation. > I wonder whether you think it is appropriate to acquire a lock at the > beginning of pn533_recv_frame(), and release it when > pn533_wq_cmd_complete() is finished, thus ensuring that another work > will not start when one pn533_wq_cmd_complete() work is not yet finished. I don't know this driver well enough, but it currently does not have any locking around this so it assumes pn533_recv_frame() cannot start concurrently, before complete callback finishes. This could be solved, if it makes sense. However maybe it would be enough to take: 1. Move contents of dev->cmd to another member in dev (e.g. dev->cmd_in_progress), first checking if that member is empty (then maybe wait? or return -EBUSY?) 2. dev->cmd = NULL 3. queue_work (see also explanation of barriers there) 4. The cmd_complete_work workqueue takes ownership of dev->cmd_in_progress and NULL-ifies it at end of work + barrier. Best regards, Krzysztof