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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS 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 0A149C43387 for ; Wed, 16 Jan 2019 14:34:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BEB4A20675 for ; Wed, 16 Jan 2019 14:34:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2393637AbfAPOeW (ORCPT ); Wed, 16 Jan 2019 09:34:22 -0500 Received: from mail.kernel.org ([198.145.29.99]:40594 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387533AbfAPOeV (ORCPT ); Wed, 16 Jan 2019 09:34:21 -0500 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 5C09E206C2; Wed, 16 Jan 2019 14:34:20 +0000 (UTC) Date: Wed, 16 Jan 2019 09:34:18 -0500 From: Steven Rostedt To: Masami Hiramatsu Cc: Andreas Ziegler , Ingo Molnar , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] tracing/uprobes: Fix output for multiple string arguments Message-ID: <20190116093418.2fe3e96b@gandalf.local.home> In-Reply-To: <20190116141629.5752-1-andreas.ziegler@fau.de> References: <20190116084021.34b0beee@gandalf.local.home> <20190116141629.5752-1-andreas.ziegler@fau.de> X-Mailer: Claws Mail 3.16.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 16 Jan 2019 15:16:29 +0100 Andreas Ziegler wrote: > When printing multiple uprobe arguments as strings the output for the > earlier arguments would also include all later string arguments. > > This is best explained in an example: > > Consider adding a uprobe to a function receiving two strings as > parameters which is at offset 0xa0 in strlib.so and we want to print > both parameters when the uprobe is hit (on x86_64): > > $ echo 'p:func /lib/strlib.so:0xa0 +0(%di):string +0(%si):string' > \ > /sys/kernel/debug/tracing/uprobe_events > > When the function is called as func("foo", "bar") and we hit the probe, > the trace file shows a line like the following: > > [...] func: (0x7f7e683706a0) arg1="foobar" arg2="bar" > > Note the extra "bar" printed as part of arg1. This behaviour stacks up > for additional string arguments. > > The strings are stored in a dynamically growing part of the uprobe > buffer by fetch_store_string() after copying them from userspace via > strncpy_from_user(). The return value of strncpy_from_user() is then > directly used as the required size for the string. However, this does > not take the terminating null byte into account as the documentation > for strncpy_from_user() cleary states that it "[...] returns the > length of the string (not including the trailing NUL)" even though the > null byte will be copied to the destination. > > Therefore, subsequent calls to fetch_store_string() will overwrite > the terminating null byte of the most recently fetched string with > the first character of the current string, leading to the > "accumulation" of strings in earlier arguments in the output. > > Fix this by incrementing the return value of strncpy_from_user() by > one if we did not hit the maximum buffer size. > > Signed-off-by: Andreas Ziegler Masami, Care to give a Reviewed-by on this patch? -- Steve > --- > v2: removed a wrong check for (ret > 0) > > kernel/trace/trace_uprobe.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c > index e335576b9411..3a1d5ab6b4ba 100644 > --- a/kernel/trace/trace_uprobe.c > +++ b/kernel/trace/trace_uprobe.c > @@ -160,6 +160,13 @@ fetch_store_string(unsigned long addr, void *dest, void *base) > if (ret >= 0) { > if (ret == maxlen) > dst[ret - 1] = '\0'; > + else > + /* > + * Include the terminating null byte. In this case it > + * was copied by strncpy_from_user but not accounted > + * for in ret. > + */ > + ret++; > *(u32 *)dest = make_data_loc(ret, (void *)dst - base); > } > > -- > 2.17.1