Subject: [PATCH 2573/2944] tracing: Fix race in trace_open and buffer resize call

From: Gaurav Kohli <[email-masked]>
Date: Tue, 6 Oct 2020 15:03:53 +0530

to #27338374

commit bbeb97464eefc65f506084fd9f18f21653e01137 upstream.

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.

Take buffer lock to fix this.

Link: https://lkml.kernel.org/r/[email-masked]

Cc: [email-masked]
Fixes: 83f40318dab00 ("ring-buffer: Make removal of ring buffer pages atomic")
Reported-by: Denis Efremov <[email-masked]>
Signed-off-by: Gaurav Kohli <[email-masked]>
Signed-off-by: Steven Rostedt (VMware) <[email-masked]>
Signed-off-by: Greg Kroah-Hartman <[email-masked]>

Fixes: CVE-2020-27825
Signed-off-by: Shile Zhang <[email-masked]>
Acked-by: Joseph Qi <[email-masked]>
---
 kernel/trace/ring_buffer.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 805aef8..763e03a 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -4359,6 +4359,8 @@ void ring_buffer_reset_cpu(struct ring_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(&buffer->resize_disabled);
 	atomic_inc(&cpu_buffer->record_disabled);
@@ -4382,6 +4384,8 @@ void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu)
 
 	atomic_dec(&cpu_buffer->record_disabled);
 	atomic_dec(&buffer->resize_disabled);
+
+	mutex_unlock(&buffer->mutex);
 }
 EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
 
-- 
1.8.3.1