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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-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 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.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) { \ -- 2.18.0 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel