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=-11.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 083F8C04AAE for ; Wed, 8 May 2019 20:25:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CD15B217D4 for ; Wed, 8 May 2019 20:25:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729031AbfEHUZG (ORCPT ); Wed, 8 May 2019 16:25:06 -0400 Received: from mail.kernel.org ([198.145.29.99]:35160 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728837AbfEHUYz (ORCPT ); Wed, 8 May 2019 16:24:55 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 84B962173B; Wed, 8 May 2019 20:24:54 +0000 (UTC) Received: from rostedt by gandalf.local.home with local (Exim 4.92) (envelope-from ) id 1hOT7V-0007ji-Ku; Wed, 08 May 2019 16:24:53 -0400 Message-Id: <20190508202453.536550511@goodmis.org> User-Agent: quilt/0.65 Date: Wed, 08 May 2019 16:24:38 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Ingo Molnar , Andrew Morton , Orit Wasserman , Oleg Nesterov , Ingo Molnar , stable@vger.kernel.org, Elazar Leibovich Subject: [for-next][PATCH 11/13] tracing: Fix partial reading of trace events id file References: <20190508202427.252736423@goodmis.org> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Elazar Leibovich 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) --- 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 81c038ed6cee..0ce3db67f556 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -1319,9 +1319,6 @@ 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