ring-buffer: Check for uninitialized cpu buffer before resizing

With a system where, num_present_cpus < num_possible_cpus, even if all
CPUs are online, non-present CPUs don't have per_cpu buffers allocated.
If per_cpu/<cpu>/buffer_size_kb is modified for such a CPU, it can cause
a panic due to NULL dereference in ring_buffer_resize().

To fix this, resize operation is allowed only if the per-cpu buffer has
been initialized.

Link: http://lkml.kernel.org/r/1349912427-6486-1-git-send-email-vnagarnaik@google.com
Cc: stable@vger.kernel.org # 3.5+
Signed-off-by: Vaibhav Nagarnaik <vnagarnaik@google.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index b32ed0e385a59b40b971bd04e0e374d333992749..b979426d16c6efc48e743b6a9df48a78bcaa9f4b 100644 (file)
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1567,6 +1567,10 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size,
 
                put_online_cpus();
        } else {
+               /* Make sure this CPU has been intitialized */
+               if (!cpumask_test_cpu(cpu_id, buffer->cpumask))
+                       goto out;
+
                cpu_buffer = buffer->buffers[cpu_id];
 
                if (nr_pages == cpu_buffer->nr_pages)