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 944D9C43387 for ; Thu, 17 Jan 2019 07:58:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 596F120856 for ; Thu, 17 Jan 2019 07:58:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1547711892; bh=k737BUtgiJSYQxUnNYSqndlyw5oWbBeoTcKQjicgsE0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=Bg06sY2oUlzmNJPv+ZAGnP9f4e6kgv0m3b3PdWTeCWkTGRM9TS3q+PVRYpPPkf88K fl0+Xv1NGFi9k5ThIQc+1aNRC7ZNgBULDUWUd1+rlbenlbDE4d6RMPVz1+zkgvY+bG WF6oKv2uKZGy0riA37MYqeaQIWaONIsTXgi6HJMY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728549AbfAQH6K (ORCPT ); Thu, 17 Jan 2019 02:58:10 -0500 Received: from mail.kernel.org ([198.145.29.99]:60384 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726796AbfAQH6K (ORCPT ); Thu, 17 Jan 2019 02:58:10 -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 E6F6320851; Thu, 17 Jan 2019 07:58:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1547711889; bh=k737BUtgiJSYQxUnNYSqndlyw5oWbBeoTcKQjicgsE0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=prZRNz75WgtRRIvSQejvI5H5982OVLJ6nN6joDf9kJFW493X9qfepdSgEtpaeu0XA hEO6fbi1lBDZ+cZgkrWJaIQhlrxUOrnfeAdJq0rvl0BGqiJtBChE5rckr2pwaJhmhS qTSpjj5n58eNW593gtXm3zDe7Z3+sulzopT84uHE= Date: Thu, 17 Jan 2019 16:58:07 +0900 From: Masami Hiramatsu To: Andreas Ziegler Cc: Steven Rostedt , Ingo Molnar , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] tracing/uprobes: Fix output for multiple string arguments Message-Id: <20190117165807.64e95553ff397e7f73ba495b@kernel.org> In-Reply-To: References: <20190116084021.34b0beee@gandalf.local.home> <20190116141629.5752-1-andreas.ziegler@fau.de> <20190117150107.17f2c0c37e41126120c5eebb@kernel.org> 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 Thu, 17 Jan 2019 08:40:05 +0100 Andreas Ziegler wrote: > On 17.01.19 07:01, Masami Hiramatsu wrote: > > 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) > > > > I don't think we need to increase that since the documentation for > strnlen_user() says that it "[r]eturns the size of the string > INCLUDING the terminating NUL." so its return value will already be > one more than that of strncpy_from_user(). Ah, I got it. Hmm, in that case, I have to update my patch in the previous mail. Anyway, Acked-by: Masami Hiramatsu Thank you!! > > Thanks, > > Andreas > > > 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