From nobody Thu Apr 9 13:31:27 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 904A7C43217 for ; Sat, 5 Nov 2022 20:51:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229939AbiKEUvP (ORCPT ); Sat, 5 Nov 2022 16:51:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49302 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229479AbiKEUvK (ORCPT ); Sat, 5 Nov 2022 16:51:10 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D1248EE29; Sat, 5 Nov 2022 13:51:09 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 5C4AF60B40; Sat, 5 Nov 2022 20:51:09 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C2A58C433B5; Sat, 5 Nov 2022 20:51:08 +0000 (UTC) Received: from rostedt by gandalf.local.home with local (Exim 4.96) (envelope-from ) id 1orQ8f-007k79-1h; Sat, 05 Nov 2022 16:51:37 -0400 Message-ID: <20221105205137.364862227@goodmis.org> User-Agent: quilt/0.66 Date: Sat, 05 Nov 2022 16:50:50 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Andrew Morton , stable@vger.kernel.org, Steven Noonan , Takashi Iwai , Roland Ruckerbauer Subject: [for-linus][PATCH 1/6] ring-buffer: Check for NULL cpu_buffer in ring_buffer_wake_waiters() References: <20221105205049.462806482@goodmis.org> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: "Steven Rostedt (Google)" On some machines the number of listed CPUs may be bigger than the actual CPUs that exist. The tracing subsystem allocates a per_cpu directory with access to the per CPU ring buffer via a cpuX file. But to save space, the ring buffer will only allocate buffers for online CPUs, even though the CPU array will be as big as the nr_cpu_ids. With the addition of waking waiters on the ring buffer when closing the file, the ring_buffer_wake_waiters() now needs to make sure that the buffer is allocated (with the irq_work allocated with it) before trying to wake waiters, as it will cause a NULL pointer dereference. While debugging this, I added a NULL check for the buffer itself (which is OK to do), and also NULL pointer checks against buffer->buffers (which is not fine, and will WARN) as well as making sure the CPU number passed in is within the nr_cpu_ids (which is also not fine if it isn't). Link: https://lore.kernel.org/all/87h6zklb6n.wl-tiwai@suse.de/ Link: https://lore.kernel.org/all/CAM6Wdxc0KRJMXVAA0Y=3Du6Jh2V=3DuWB-_Fn6M4= xRuNppfXzL1mUg@mail.gmail.com/ Link: https://lkml.kernel.org/linux-trace-kernel/20221101191009.1e7378c8@ro= rschach.local.home Cc: stable@vger.kernel.org Cc: Steven Noonan Bugzilla: https://bugzilla.opensuse.org/show_bug.cgi?id=3D1204705 Reported-by: Takashi Iwai Reported-by: Roland Ruckerbauer Fixes: f3ddb74ad079 ("tracing: Wake up ring buffer waiters on closing of th= e file") Reviewed-by: Masami Hiramatsu (Google) Signed-off-by: Steven Rostedt (Google) --- kernel/trace/ring_buffer.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 199759c73519..9712083832f4 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -937,6 +937,9 @@ void ring_buffer_wake_waiters(struct trace_buffer *buff= er, int cpu) struct ring_buffer_per_cpu *cpu_buffer; struct rb_irq_work *rbwork; =20 + if (!buffer) + return; + if (cpu =3D=3D RING_BUFFER_ALL_CPUS) { =20 /* Wake up individual ones too. One level recursion */ @@ -945,7 +948,15 @@ void ring_buffer_wake_waiters(struct trace_buffer *buf= fer, int cpu) =20 rbwork =3D &buffer->irq_work; } else { + if (WARN_ON_ONCE(!buffer->buffers)) + return; + if (WARN_ON_ONCE(cpu >=3D nr_cpu_ids)) + return; + cpu_buffer =3D buffer->buffers[cpu]; + /* The CPU buffer may not have been initialized yet */ + if (!cpu_buffer) + return; rbwork =3D &cpu_buffer->irq_work; } =20 --=20 2.35.1