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=-5.2 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,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 DAC3FC282C0 for ; Thu, 24 Jan 2019 03:03:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A8885218A1 for ; Thu, 24 Jan 2019 03:03:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548299028; bh=SwbeqvMuelXlay+iLeUO0Jf2QkbnmqQyBFnYoRTRwLY=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=F2VlLpqQny3NiwNC/VpxH3VjYN1HoHFQaDGQGHI8GTqFmxwlw1D7AH1NtIAyKJCJk JKz+voqytpz6rDjmRPh8da8ij3ouliRnLYkGuBBfK8CQihYCkexWXGPJaCU8zsbp3B pWd5tyheHibP+wTnJ+dSfa+eCMwZvgNyiwawm20o= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727496AbfAXDDr (ORCPT ); Wed, 23 Jan 2019 22:03:47 -0500 Received: from mail.kernel.org ([198.145.29.99]:38692 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727126AbfAXDDq (ORCPT ); Wed, 23 Jan 2019 22:03:46 -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 3D32A21872; Thu, 24 Jan 2019 03:03:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548299025; bh=SwbeqvMuelXlay+iLeUO0Jf2QkbnmqQyBFnYoRTRwLY=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=aYBDUIxdqAtfrcRvext0vGkf2o5YOe/vYcd3jyOnW8gZy3yEwBv3YLYnZ9jLzzQNa MAJzjzFfdifr3Iw4OwQWNgYenod3CLZ3dNfFN8trxfi1cdlsCV/ooQH+0st94KjmhT Y6O95pkgzfKsK8VLCv/yAiaDdJVCh9AUGIFd6qo4= Date: Thu, 24 Jan 2019 12:03:43 +0900 From: Masami Hiramatsu To: Steven Rostedt Cc: Andreas Ziegler , Ingo Molnar , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/3] tracing: uprobes: Re-enable $comm support for uprobe events Message-Id: <20190124120343.dca2887200a50c3f3ad1186b@kernel.org> In-Reply-To: <20190123210956.0178b890@vmware.local.home> References: <154778663676.19927.12774448308165809570.stgit@devbox> <154778666570.19927.5960654930869453736.stgit@devbox> <20190123034005.2b49e4fe@vmware.local.home> <20190124104322.29e62ee0024c77a40110d569@kernel.org> <20190123210956.0178b890@vmware.local.home> 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, 23 Jan 2019 21:09:56 -0500 Steven Rostedt wrote: > On Thu, 24 Jan 2019 10:43:22 +0900 > Masami Hiramatsu wrote: > > > > > kernel/trace/trace_uprobe.c | 15 +++++++++++++-- > > > > 1 file changed, 13 insertions(+), 2 deletions(-) > > > > > > > > diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c > > > > index 3a1d5ab6b4ba..b07e498ccbc6 100644 > > > > --- a/kernel/trace/trace_uprobe.c > > > > +++ b/kernel/trace/trace_uprobe.c > > > > @@ -156,7 +156,10 @@ fetch_store_string(unsigned long addr, void *dest, void *base) > > > > if (unlikely(!maxlen)) > > > > return -ENOMEM; > > > > > > > > - ret = strncpy_from_user(dst, src, maxlen); > > > > + if (addr == (unsigned long)current->comm) > > > > + ret = strlcpy(dst, current->comm, maxlen); > > > > > > As user space (although only root) defines the size of the event being > > > stored, and we could trick addr to be current->comm (although > > > difficult), we could possibly leak data if maxlen is > TASK_COMM_LEN. I > > > would feel better if we tested maxlen against TASK_COMM_LEN in this > > > case. > > > > > > if (maxlen > TASK_COMM_LEN) > > > maxlen = TASK_COMM_LEN; > > > > > > Or if we don't think it can happen, add a WARN_ON(maxlen > > > > TASK_COMM_LEN). > > > > Hmm, I thought current->comm is null terminated, isn't it? > > Yes it is. I was thinking it was a memcpy (I blame conference fatigue ;-) > > > Anyway, if user can specify current->comm, he must be able to specify > > current->comm + TASK_COMM_LEN too by kprobe_events. > > Moreover, it can leak any data in kernel... > > But this is for uprobes, which I why I was concerned. OK, what we will leak by this, is the address of current->comm to root user for a specific application running instance. Since they can try to write a data on a register and trace it like "+0(%ax):string" and if rax register has hit the current->comm, uprobe event will record comm, but other case, it will show "(fault)". So they can trial and error on that (but leaking just a temporary task instance address). If you concern this, I can change it to store a special fixed value, like (unsigned long)-EINVAL, instead of current->comm address. :-) > > And also, maxlen is calculated by fetch_store_strlen, right before > > this has been called. > > > > I rather concern the case that if we have shorter size of maxlen than > > current->comm. Would we better show "(fault)" or tail-cut name ? > > (of course this is very difficult to happen, since the length is > > already checked.) > > Actually, it would still be OK, as strlcpy does guarantee to be nul > terminated as long as it's greater than zero. Ah, I meant that we can record a shorter name, like "shutdown" -> "sh". > Hmm, strlcpy doesn't pad the rest if what is written is shorter than > what is allocated. Could that leak data? Even though, there should be a data that had been recorded on the ring buffer. Thank you, -- Masami Hiramatsu