stable.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Denis Efremov <efremov@linux.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Gaurav Kohli <gkohli@codeaurora.org>,
	linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
	stable@vger.kernel.org, Julia Lawall <julia.lawall@inria.fr>
Subject: Re: [PATCH v1] trace: Fix race in trace_open and buffer resize call
Date: Thu, 21 Jan 2021 23:15:22 +0300	[thread overview]
Message-ID: <021b1b38-47ce-bc8b-3867-99160cc85523@linux.com> (raw)
In-Reply-To: <20210121140951.2a554a5e@gandalf.local.home>



On 1/21/21 10:09 PM, Steven Rostedt wrote:
> On Thu, 21 Jan 2021 17:30:40 +0300
> Denis Efremov <efremov@linux.com> wrote:
> 
>> Hi,
>>
>> This patch (CVE-2020-27825) was tagged with
>> Fixes: b23d7a5f4a07a ("ring-buffer: speed up buffer resets by avoiding synchronize_rcu for each CPU")
>>
>> I'm not an expert here but it seems like b23d7a5f4a07a only refactored
>> ring_buffer_reset_cpu() by introducing reset_disabled_cpu_buffer() without
>> significant changes. Hence, mutex_lock(&buffer->mutex)/mutex_unlock(&buffer->mutex)
>> can be backported further than b23d7a5f4a07a~ and to all LTS kernels. Is
>> b23d7a5f4a07a the actual cause of the bug?
>>
> 
> Ug, that looks to be a mistake. Looking back at the thread about this:
> 
>   https://lore.kernel.org/linux-arm-msm/20200915141304.41fa7c30@gandalf.local.home/

I see from the link that it was planned to backport the patch to LTS kernels:

> Actually we are seeing issue in older kernel like 4.19/4.14/5.4 and there below patch was not 
> present in stable branches:
> Commit b23d7a5f4a07 ("ring-buffer: speed up buffer resets by avoiding synchronize_rcu for each CPU")

The point is that it's not backported yet. Maybe because of Fixes tag. I've discovered
this while trying to formalize CVE-2020-27825 bug in cvehound
https://github.com/evdenis/cvehound/blob/master/cvehound/cve/CVE-2020-27825.cocci

I think that the backport to the 4.4+ should be something like:

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 547a3a5ac57b..2171b377bbc1 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -4295,6 +4295,8 @@ void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu)
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
 		return;
 
+	mutex_lock(&buffer->mutex);
+
 	atomic_inc(&buffer->resize_disabled);
 	atomic_inc(&cpu_buffer->record_disabled);
 
@@ -4317,6 +4319,8 @@ void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu)
 
 	atomic_dec(&cpu_buffer->record_disabled);
 	atomic_dec(&buffer->resize_disabled);
+
+	mutex_unlock(&buffer->mutex);
 }
 EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
 

Thanks,
Denis






  reply	other threads:[~2021-01-21 20:16 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-06  9:33 Gaurav Kohli
2021-01-21 14:30 ` Denis Efremov
2021-01-21 19:09   ` Steven Rostedt
2021-01-21 20:15     ` Denis Efremov [this message]
2021-01-21 20:37       ` Steven Rostedt
2021-01-22 10:59         ` Greg KH
2021-01-22 11:25           ` Gaurav Kohli
2021-01-22 14:37             ` Steven Rostedt
2021-01-23 10:49               ` Denis Efremov
2021-01-23 16:33                 ` Gaurav Kohli
2021-01-24  3:21                   ` Steven Rostedt
2021-01-24  9:57                     ` Gaurav Kohli
2021-01-24 10:05                       ` Greg KH
  -- strict thread matches above, loose matches on Subject: below --
2020-09-24 13:55 Gaurav Kohli
2020-10-05  4:39 ` Gaurav Kohli
2020-10-05 14:25   ` Steven Rostedt
2020-10-05 14:27     ` Steven Rostedt
2020-10-05 16:29       ` Gaurav Kohli
2020-10-05 16:32         ` Steven Rostedt
2020-10-05 17:38           ` Gaurav Kohli

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=021b1b38-47ce-bc8b-3867-99160cc85523@linux.com \
    --to=efremov@linux.com \
    --cc=gkohli@codeaurora.org \
    --cc=julia.lawall@inria.fr \
    --cc=linux-arm-msm@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=rostedt@goodmis.org \
    --cc=stable@vger.kernel.org \
    --subject='Re: [PATCH v1] trace: Fix race in trace_open and buffer resize call' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).