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=-11.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,T_DKIMWL_WL_HIGH,URIBL_BLOCKED, USER_AGENT_GIT 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 B0CA7C282DD for ; Thu, 23 May 2019 19:47:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 865D920881 for ; Thu, 23 May 2019 19:47:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1558640848; bh=DSUmzvgjUNMwYATk24t7LKBls8lxxLoyxNRXEDvqXbI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=P85bKnI6dqAo7QxA6/u9fXN72TsSMpleDu/+AZDWMi3RAY9HBh7/Hh1RR0dS7o5E5 pcoS5kcB5JRqfwF56UfPH6r21ZPXTu3XyDO9VWWOS2imp3yqK00PP0fRU1CawPT9Ph J+gzpSOJsxHY8H1knUgj/2FDgncumXgUNZAZ7Y8A= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388909AbfEWTr1 (ORCPT ); Thu, 23 May 2019 15:47:27 -0400 Received: from mail.kernel.org ([198.145.29.99]:46852 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387603AbfEWTNB (ORCPT ); Thu, 23 May 2019 15:13:01 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (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 D262120863; Thu, 23 May 2019 19:12:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1558638780; bh=DSUmzvgjUNMwYATk24t7LKBls8lxxLoyxNRXEDvqXbI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=mlZTEyTSVldJQS99Ptu9rwpYeg6XcoMOJaJz3EctBqOjB4j0YewR9XrjtaxiKd/5m +FY6sVidGSrRR3anI7zXzXF9CV1Bh53xLZxEkeXyfE0SfcbFPlGFHFg2OTaEBBleaO Pxom5eS2kFVyGGVjxyb71QTqWYb3ntR0jBRrWUf4= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Orit Wasserman , Oleg Nesterov , Ingo Molnar , Elazar Leibovich , "Steven Rostedt (VMware)" Subject: [PATCH 4.14 35/77] tracing: Fix partial reading of trace events id file Date: Thu, 23 May 2019 21:05:53 +0200 Message-Id: <20190523181725.069959999@linuxfoundation.org> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190523181719.982121681@linuxfoundation.org> References: <20190523181719.982121681@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 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 commit cbe08bcbbe787315c425dde284dcb715cfbf3f39 upstream. 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: Greg Kroah-Hartman --- kernel/trace/trace_events.c | 3 --- 1 file changed, 3 deletions(-) --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -1319,9 +1319,6 @@ event_id_read(struct file *filp, char __ char buf[32]; int len; - if (*ppos) - return 0; - if (unlikely(!id)) return -ENODEV;