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ring-buffer: Check for NULL cpu_buffer in ring_buffer_wake_waiters()

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commit 7433632c9ff68a991bd0bc38cabf354e9d2de410 upstream.

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=u6Jh2V=uWB-_Fn6M4xRuNppfXzL1mUg@mail.gmail.com/
Link: https://lkml.kernel.org/linux-trace-kernel/20221101191009.1e7378c8@rorschach.local.home

Cc: stable@vger.kernel.org
Cc: Steven Noonan <steven.noonan@gmail.com>
Bugzilla: https://bugzilla.opensuse.org/show_bug.cgi?id=1204705
Reported-by: Takashi Iwai <tiwai@suse.de>
Reported-by: Roland Ruckerbauer <roland.rucky@gmail.com>
Fixes: f3ddb74ad079 ("tracing: Wake up ring buffer waiters on closing of the file")
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Steven Rostedt (Google) 2022-11-01 19:10:09 -04:00 committed by Greg Kroah-Hartman
parent 85f3caa955
commit b5074df412
1 changed files with 11 additions and 0 deletions
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11
kernel/trace/ring_buffer.c
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@ -901,6 +901,9 @@ void ring_buffer_wake_waiters(struct trace_buffer *buffer, int cpu)
struct ring_buffer_per_cpu *cpu_buffer;
struct rb_irq_work *rbwork;
if (!buffer)
return;
if (cpu == RING_BUFFER_ALL_CPUS) {
/* Wake up individual ones too. One level recursion */
@ -909,7 +912,15 @@ void ring_buffer_wake_waiters(struct trace_buffer *buffer, int cpu)
rbwork = &buffer->irq_work;
} else {
if (WARN_ON_ONCE(!buffer->buffers))
return;
if (WARN_ON_ONCE(cpu >= nr_cpu_ids))
return;
cpu_buffer = buffer->buffers[cpu];
/* The CPU buffer may not have been initialized yet */
if (!cpu_buffer)
return;
rbwork = &cpu_buffer->irq_work;
}