From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B195BC34026 for ; Tue, 18 Feb 2020 12:44:17 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 7C1CF2173E for ; Tue, 18 Feb 2020 12:44:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="PPOU1Nrv" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7C1CF2173E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=zeniv.linux.org.uk Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-mediatek-bounces+linux-mediatek=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=p+O7Z8t8lYtD7pdYw22hexTNmQlCuyu+fdnu6BSMfcw=; b=PPOU1NrvMrLmr0 BXAlAE3YsgELzOPLQmLuH+PC2a8zSV2XRiKVcn+EZRcYvpvouz/XTaBmveiZyz5x3rmdyNMkFPn0w 1PsXNXTzGEOtVMw2OtKEkFQhYGjhfSBSlmXCxIxeqbZmAUUY5J/WtJiA+UagXbp0D39THjYtZxGu7 BOQ/ZIFKnn4tWWIDIuTocKBTCiprbVj5T4zTxj7d9xOXtkrOwFjDfnu8AptzzcX5Aleuk1iConxcu LsGAn9g7EZ0WJcxvzNyBhzmomLdCnpuu+LE70bjWlBWjAWrU1LccjHiHEystGa+hMugPxQzyluu10 bp6FB5W4apd9MfYSKlsg==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1j42EU-0000Yc-VV; Tue, 18 Feb 2020 12:44:11 +0000 Received: from zeniv.linux.org.uk ([195.92.253.2]) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1j42EM-0000HK-OP; Tue, 18 Feb 2020 12:44:04 +0000 Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1j42C6-00Efka-5Y; Tue, 18 Feb 2020 12:41:42 +0000 Date: Tue, 18 Feb 2020 12:41:42 +0000 From: Al Viro To: Macpaul Lin Subject: Re: [PATCH] lib: iov_iter.c: fix a possible calculation error on remaining bytes Message-ID: <20200218124142.GJ23230@ZenIV.linux.org.uk> References: <1582011672-17189-1-git-send-email-macpaul.lin@mediatek.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <1582011672-17189-1-git-send-email-macpaul.lin@mediatek.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200218_044402_793506_7D268C6F X-CRM114-Status: GOOD ( 17.85 ) X-BeenThere: linux-mediatek@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Sasha Levin , Shen Jing , CC Hwang , Mediatek WSD Upstream , Jerry Zhang , linux-usb@vger.kernel.org, Loda Chou , linux-kernel@vger.kernel.org, Andrzej Pietrasiewicz , John Stultz , Vincent Pelletier , Matthias Brugger , linux-mediatek@lists.infradead.org, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "Linux-mediatek" Errors-To: linux-mediatek-bounces+linux-mediatek=archiver.kernel.org@lists.infradead.org On Tue, Feb 18, 2020 at 03:41:12PM +0800, Macpaul Lin wrote: > This issue was found when adbd trying to open functionfs with AIO mode. > Usually, we need to set "setprop sys.usb.ffs.aio_compat 0" to enable > adbd with AIO mode on Android. > > When adbd is opening functionfs, it will try to read 24 bytes at the > fisrt read I/O control. If this reading has been failed, adbd will > try to send FUNCTIONFS_CLEAR_HALT to functionfs. When adbd is in AIO > mode, functionfs will be acted with asyncronized I/O path. After the > successful read transfer has been completed by gadget hardware, the > following series of functions will be called. > ffs_epfile_async_io_complete() -> ffs_user_copy_worker() -> > copy_to_iter() -> _copy_to_iter() -> copyout() -> > iterate_and_advance() -> iterate_iovec() > > Adding debug trace to these functions, it has been found that in > iterate_iovec(), the calculation result of n will be turned into zero. > n = wanted - n; /* 0 == n = 24 - 24; */ > Which causes copyout() won't copy data to userspace since the length > to be copied "v.iov_len" will be zero, which isn't correct. This also > leads ffs_copy_to_iter() always return -EFAULT. Finally adbd cannot > open functionfs and send FUNCTIONFS_CLEAR_HALT. > > Signed-off-by: Macpaul Lin > --- > lib/iov_iter.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/lib/iov_iter.c b/lib/iov_iter.c > index fb29c02c6a3c..f9334144e259 100644 > --- a/lib/iov_iter.c > +++ b/lib/iov_iter.c > @@ -36,7 +36,8 @@ > skip = __v.iov_len; \ > n -= __v.iov_len; \ > } \ > - n = wanted - n; \ > + if (n != wanted) \ > + n = wanted - n; \ > } First of all, nothing in that line can possibly *cause* copyout() to do anything - it's after the calls of step. What's more, this changes behaviour only when wanted would've been equal to n, doesn't it? Which translates into "no decrements of n have happened at all", i.e. "nothing has been copied". IOW, it's a consequence of no copyout, not the cause of such. You can make copy_to_iter() lie and pretend if has copied everything when it has copied nothing, but that won't change the underlying bug. So I'm afraid your debugging is not finished - you still need to find out what causes the copyout failures and/or BS iov_iter padded by caller. _______________________________________________ Linux-mediatek mailing list Linux-mediatek@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-mediatek