From cfb649c63daf2b7ec693b703ee069fd003bb54ed Mon Sep 17 00:00:00 2001 From: Gaurav Kohli Date: Tue, 6 Oct 2020 15:03:53 +0530 Subject: [PATCH 2573/2944] tracing: Fix race in trace_open and buffer resize call 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/1601976833-24377-1-git-send-email-gkohli@codeaurora.org Cc: stable@vger.kernel.org Fixes: 83f40318dab00 ("ring-buffer: Make removal of ring buffer pages atomic") Reported-by: Denis Efremov Signed-off-by: Gaurav Kohli Signed-off-by: Steven Rostedt (VMware) Signed-off-by: Greg Kroah-Hartman Fixes: CVE-2020-27825 Signed-off-by: Shile Zhang Acked-by: Joseph Qi --- 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