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Mon, 17 Feb 2020 23:41:24 -0800 Received: from mtkmbs08n1.mediatek.inc (172.21.101.55) by MTKMBS62DR.mediatek.inc (172.29.94.18) with Microsoft SMTP Server (TLS) id 15.0.1395.4; Mon, 17 Feb 2020 23:41:21 -0800 Received: from mtkcas09.mediatek.inc (172.21.101.178) by mtkmbs08n1.mediatek.inc (172.21.101.55) with Microsoft SMTP Server (TLS) id 15.0.1395.4; Tue, 18 Feb 2020 15:42:30 +0800 Received: from mtkswgap22.mediatek.inc (172.21.77.33) by mtkcas09.mediatek.inc (172.21.101.73) with Microsoft SMTP Server id 15.0.1395.4 via Frontend Transport; Tue, 18 Feb 2020 15:40:51 +0800 From: Macpaul Lin To: Alexander Viro , Matthias Brugger , Shen Jing , Sasha Levin , John Stultz , Macpaul Lin , Andrzej Pietrasiewicz , Vincent Pelletier , Jerry Zhang , , , , Subject: [PATCH] lib: iov_iter.c: fix a possible calculation error on remaining bytes Date: Tue, 18 Feb 2020 15:41:12 +0800 Message-ID: <1582011672-17189-1-git-send-email-macpaul.lin@mediatek.com> X-Mailer: git-send-email 1.7.9.5 MIME-Version: 1.0 X-MTK: N X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200217_234130_143546_D7D88DAB X-CRM114-Status: GOOD ( 12.23 ) X-Spam-Score: -0.2 (/) X-Spam-Report: SpamAssassin version 3.4.3 on bombadil.infradead.org summary: Content analysis details: (-0.2 points) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at https://www.dnswl.org/, no trust [216.200.240.184 listed in list.dnswl.org] 0.0 SPF_HELO_NONE SPF: HELO does not publish an SPF Record -0.0 SPF_PASS SPF: sender matches SPF record 0.0 MIME_BASE64_TEXT RAW: Message text disguised using base64 encoding -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain -0.1 DKIM_VALID_EF Message has a valid DKIM or DK signature from envelope-from domain 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature 0.0 UNPARSEABLE_RELAY Informational: message has unparseable relay lines X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: CC Hwang , Loda Chou , Mediatek WSD Upstream Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org 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; \ } #define iterate_kvec(i, n, __v, __p, skip, STEP) { \