Re: [PATCH v1] trace: Fix race in trace_open and buffer resize call

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Hi Steven,

please let us know, if below looks good to you or need modifications.

Thanks
Gaurav

On 9/24/2020 7:25 PM, Gaurav Kohli wrote:
Below race can come, if trace_open and resize of
cpu buffer is running parallely on different cpus
CPUX                                CPUY
				    ring_buffer_resize
				    atomic_read(&buffer->resize_disabled)
tracing_open
tracing_reset_online_cpus
ring_buffer_reset_cpu
rb_reset_cpu
				    rb_update_pages
				    remove/insert pages
resetting pointer
This race can cause data abort or some times infinte loop in
rb_remove_pages and rb_insert_pages while checking pages
for sanity.

Signed-off-by: Gaurav Kohli <gkohli@xxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
Changes since v0:
   -Addressed Steven's review comments.

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 93ef0ab..15bf28b 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -4866,6 +4866,9 @@ void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu)
  	if (!cpumask_test_cpu(cpu, buffer->cpumask))
  		return;
+ /* prevent another thread from changing buffer sizes */
+	mutex_lock(&buffer->mutex);
+
  	atomic_inc(&cpu_buffer->resize_disabled);
  	atomic_inc(&cpu_buffer->record_disabled);
@@ -4876,6 +4879,8 @@ void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu) atomic_dec(&cpu_buffer->record_disabled);
  	atomic_dec(&cpu_buffer->resize_disabled);
+
+	mutex_unlock(&buffer->mutex);
  }
  EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
@@ -4889,6 +4894,9 @@ void ring_buffer_reset_online_cpus(struct trace_buffer *buffer)
  	struct ring_buffer_per_cpu *cpu_buffer;
  	int cpu;
+ /* prevent another thread from changing buffer sizes */
+	mutex_lock(&buffer->mutex);
+
  	for_each_online_buffer_cpu(buffer, cpu) {
  		cpu_buffer = buffer->buffers[cpu];
@@ -4907,6 +4915,8 @@ void ring_buffer_reset_online_cpus(struct trace_buffer *buffer)
  		atomic_dec(&cpu_buffer->record_disabled);
  		atomic_dec(&cpu_buffer->resize_disabled);
  	}
+
+	mutex_unlock(&buffer->mutex);
  }
/**


--
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center,
Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.



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