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=-8.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 E5BA2C43387 for ; Thu, 17 Jan 2019 06:01:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B54D320854 for ; Thu, 17 Jan 2019 06:01:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1547704872; bh=FYXLeHOnCfsQgImCa1I7N8JBWRVKKVdnfJxjeJJLaj4=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=trWONVLE2IaWq74RtPxCsGxcY1b5WgqaS0NTKXDigAhi4Exge4SrGqfKcSQCa2Mtl QukOpiI0NGHVw92pjSbR1NiouGQcAbSwUm+zNcEZq//xON+21d2fDjZyEhCTcRAulx wgiRkFo+0srSDNaPyiAQISq7xUYFGCo7OYYqezDM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729874AbfAQGBL (ORCPT ); Thu, 17 Jan 2019 01:01:11 -0500 Received: from mail.kernel.org ([198.145.29.99]:39900 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725320AbfAQGBK (ORCPT ); Thu, 17 Jan 2019 01:01:10 -0500 Received: from devbox (NE2965lan1.rev.em-net.ne.jp [210.141.244.193]) (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 15FB420657; Thu, 17 Jan 2019 06:01:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1547704870; bh=FYXLeHOnCfsQgImCa1I7N8JBWRVKKVdnfJxjeJJLaj4=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=bA8VPaxrGKiKwWsnrq+h6R7nNoYjFU1yUzjzNKxWe7gpo0q74ohu4OHxZfNbJOkOn recDU94vytnabiXaZRQRBgaFwDFtVjbTo4P2oxXVk7SoK2zwG+AgszRoAZM9yGsKek bpNnYtOMKQn9AFaJSZcX13kxWcdAkRtUbB1GSmGY= Date: Thu, 17 Jan 2019 15:01:07 +0900 From: Masami Hiramatsu To: Andreas Ziegler Cc: Steven Rostedt , Ingo Molnar , Masami Hiramatsu , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] tracing/uprobes: Fix output for multiple string arguments Message-Id: <20190117150107.17f2c0c37e41126120c5eebb@kernel.org> 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: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-redhat-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. > Yeah, I had eventually same conclusion. However, you also have to increse the return value of fetch_store_strlen() too. (And I found another issue) Could you fix fetch_store_strlen in the same patch? Thank you, > Signed-off-by: Andreas Ziegler > --- > 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 > -- Masami Hiramatsu