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=-14.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,T_DKIMWL_WL_HIGH,URIBL_BLOCKED, USER_AGENT_GIT autolearn=ham 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 A6EECC28CC1 for ; Sat, 1 Jun 2019 13:26:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 80AE6273E2 for ; Sat, 1 Jun 2019 13:26:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1559395596; bh=AMh3azfDv9eQJGwB33I3PMFCyzDsud9Khu23J1NMkyw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=dWS52p1a72yWg9nwXwy2lOZz/+9/xfCnXaMLfCg8hp+SK/0k/+WyiTd3N/7woHNYI wtvh/mXd5KZ2xPQaMNVpdlMpuEkk6EOcF8ET3cmBHu5OLca4eyUPrHjAL70kEloN/B mNOspeEhp+aL+aI7SAWEkUkaAW4usrBMfpbiwOVw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729744AbfFAN0f (ORCPT ); Sat, 1 Jun 2019 09:26:35 -0400 Received: from mail.kernel.org ([198.145.29.99]:56964 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729722AbfFAN0b (ORCPT ); Sat, 1 Jun 2019 09:26:31 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 6A9AA273CD; Sat, 1 Jun 2019 13:26:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1559395591; bh=AMh3azfDv9eQJGwB33I3PMFCyzDsud9Khu23J1NMkyw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=YnkKdvNYlk/SnNUN3aJmEeQDCT5iqUrpYfXB65ImIGMGJxDA9D/nraSwUrlhhvAFW ffzgEpnSdeI2PecBBFJrU7kOLQl52KenxTXAxvPrbWjdN4hCDJZvf0lAgG9YKDY5hL QlMKRfYHjoEky0WVlcBPGQnL64AU6kNjKzXxEBsk= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Elazar Leibovich , Orit Wasserman , Oleg Nesterov , Ingo Molnar , Steven Rostedt , Sasha Levin Subject: [PATCH AUTOSEL 4.4 16/56] tracing: Fix partial reading of trace event's id file Date: Sat, 1 Jun 2019 09:25:20 -0400 Message-Id: <20190601132600.27427-16-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190601132600.27427-1-sashal@kernel.org> References: <20190601132600.27427-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Elazar Leibovich [ Upstream commit cbe08bcbbe787315c425dde284dcb715cfbf3f39 ] When reading only part of the id file, the ppos isn't tracked correctly. This is taken care by simple_read_from_buffer. Reading a single byte, and then the next byte would result EOF. While this seems like not a big deal, this breaks abstractions that reads information from files unbuffered. See for example https://github.com/golang/go/issues/29399 This code was mentioned as problematic in commit cd458ba9d5a5 ("tracing: Do not (ab)use trace_seq in event_id_read()") An example C code that show this bug is: #include #include #include #include #include #include int main(int argc, char **argv) { if (argc < 2) return 1; int fd = open(argv[1], O_RDONLY); char c; read(fd, &c, 1); printf("First %c\n", c); read(fd, &c, 1); printf("Second %c\n", c); } Then run with, e.g. sudo ./a.out /sys/kernel/debug/tracing/events/tcp/tcp_set_state/id You'll notice you're getting the first character twice, instead of the first two characters in the id file. Link: http://lkml.kernel.org/r/20181231115837.4932-1-elazar@lightbitslabs.com Cc: Orit Wasserman Cc: Oleg Nesterov Cc: Ingo Molnar Cc: stable@vger.kernel.org Fixes: 23725aeeab10b ("ftrace: provide an id file for each event") Signed-off-by: Elazar Leibovich Signed-off-by: Steven Rostedt (VMware) Signed-off-by: Sasha Levin --- kernel/trace/trace_events.c | 3 --- 1 file changed, 3 deletions(-) diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index ba5392807912b..bd4c0bb61ad72 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -1288,9 +1288,6 @@ event_id_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos) char buf[32]; int len; - if (*ppos) - return 0; - if (unlikely(!id)) return -ENODEV; -- 2.20.1