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Subject[PATCH] ring-buffer: Check for uninitialized cpu buffer before resizing
Date
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.

Signed-off-by: Vaibhav Nagarnaik <vnagarnaik@google.com>
---
kernel/trace/ring_buffer.c | 4 ++++
1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index b32ed0e..b979426 100644
--- 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)
--
1.7.7.3


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