[PATCH 3/6] tracing: Have tracing_max_latency inc the trace array ref count

[Steven Rostedt]

From: "Steven Rostedt (Google)" <rostedt@xxxxxxxxxxx>

The tracing_max_latency file points to the trace_array max_latency field.
For an instance, if the file is opened and the instance is deleted,
reading or writing to the file will cause a use after free.

Up the ref count of the trace_array when tracing_max_latency is opened.

Link: https://lore.kernel.org/all/1cb3aee2-19af-c472-e265-05176fe9bd84@xxxxxxxxxx/

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 8530dec63e7b4 ("tracing: Add tracing_check_open_get_tr()")
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
---
 kernel/trace/trace.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 0827037ee3b8..c8b8b4c6feaf 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1772,7 +1772,7 @@ static void trace_create_maxlat_file(struct trace_array *tr,
 	init_irq_work(&tr->fsnotify_irqwork, latency_fsnotify_workfn_irq);
 	tr->d_max_latency = trace_create_file("tracing_max_latency",
 					      TRACE_MODE_WRITE,
-					      d_tracer, &tr->max_latency,
+					      d_tracer, tr,
 					      &tracing_max_lat_fops);
 }
 
@@ -1805,7 +1805,7 @@ void latency_fsnotify(struct trace_array *tr)
 
 #define trace_create_maxlat_file(tr, d_tracer)				\
 	trace_create_file("tracing_max_latency", TRACE_MODE_WRITE,	\
-			  d_tracer, &tr->max_latency, &tracing_max_lat_fops)
+			  d_tracer, tr, &tracing_max_lat_fops)
 
 #endif
 
@@ -6717,14 +6717,18 @@ static ssize_t
 tracing_max_lat_read(struct file *filp, char __user *ubuf,
 		     size_t cnt, loff_t *ppos)
 {
-	return tracing_nsecs_read(filp->private_data, ubuf, cnt, ppos);
+	struct trace_array *tr = filp->private_data;
+
+	return tracing_nsecs_read(&tr->max_latency, ubuf, cnt, ppos);
 }
 
 static ssize_t
 tracing_max_lat_write(struct file *filp, const char __user *ubuf,
 		      size_t cnt, loff_t *ppos)
 {
-	return tracing_nsecs_write(filp->private_data, ubuf, cnt, ppos);
+	struct trace_array *tr = filp->private_data;
+
+	return tracing_nsecs_write(&tr->max_latency, ubuf, cnt, ppos);
 }
 
 #endif
@@ -7778,10 +7782,11 @@ static const struct file_operations tracing_thresh_fops = {
 
 #ifdef CONFIG_TRACER_MAX_TRACE
 static const struct file_operations tracing_max_lat_fops = {
-	.open		= tracing_open_generic,
+	.open		= tracing_open_generic_tr,
 	.read		= tracing_max_lat_read,
 	.write		= tracing_max_lat_write,
 	.llseek		= generic_file_llseek,
+	.release	= tracing_release_generic_tr,
 };
 #endif
 
-- 
2.40.1