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=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 6E9BEC34037 for ; Tue, 18 Feb 2020 12:41:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4D93D2173E for ; Tue, 18 Feb 2020 12:41:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726582AbgBRMl4 (ORCPT ); Tue, 18 Feb 2020 07:41:56 -0500 Received: from zeniv.linux.org.uk ([195.92.253.2]:51288 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726512AbgBRMlz (ORCPT ); Tue, 18 Feb 2020 07:41:55 -0500 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 Cc: Matthias Brugger , Shen Jing , Sasha Levin , John Stultz , Andrzej Pietrasiewicz , Vincent Pelletier , Jerry Zhang , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, Mediatek WSD Upstream , CC Hwang , Loda Chou 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-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1582011672-17189-1-git-send-email-macpaul.lin@mediatek.com> Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.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.