tracing: probes: Fix a possible race in trace_probe_log APIs

From: Masami Hiramatsu (Google) <[email protected]>

Since the shared trace_probe_log variable can be accessed and modified via probe event create operation of kprobe_events, uprobe_events, and dynamic_events, it should be protected. In the dynamic_events, all operations are serialized by dyn_event_ops_mutex. But kprobe_events and uprobe_events interfaces are not serialized.

To solve this issue, introduces dyn_event_create(), which runs create() operation under the mutex, for kprobe_events and uprobe_events. This also uses lockdep to check the mutex is held when using trace_probe_log* APIs.

Reported-by Paul Cacheux <[email protected]>

Closes https://lore.kernel.org/all/[email protected]/ open here

Signed-off-by Masami Hiramatsu (Google) <[email protected]>

---
 kernel/trace/trace_dynevent.c |   16 +++++++++++++++-
 kernel/trace/trace_dynevent.h |    1 +
 kernel/trace/trace_kprobe.c   |    2 +-
 kernel/trace/trace_probe.c    |    9 +++++++++
 kernel/trace/trace_uprobe.c   |    2 +-
 5 files changed, 27 insertions(+), 3 deletions(-)

kernel/trace/trace_dynevent.c +15 -1

index a322e4f249a5..5d64a18cacac 100644
@@ -16,7 +16,7 @@
 #include "trace_output.h"	/* for trace_event_sem */
 #include "trace_dynevent.h"
 
-static DEFINE_MUTEX(dyn_event_ops_mutex);
+DEFINE_MUTEX(dyn_event_ops_mutex);
 static LIST_HEAD(dyn_event_ops_list);
 
 bool trace_event_dyn_try_get_ref(struct trace_event_call *dyn_call)

@@ -116,6 +116,20 @@ int dyn_event_release(const char *raw_command, struct dyn_event_operations *type
 	return ret;
 }
 
+/*
+ * Locked version of event creation. The event creation must be protected by
+ * dyn_event_ops_mutex because of protecting trace_probe_log.
+ */
+int dyn_event_create(const char *raw_command, struct dyn_event_operations *type)
+{
+	int ret;
+
+	mutex_lock(&dyn_event_ops_mutex);
+	ret = type->create(raw_command);
+	mutex_unlock(&dyn_event_ops_mutex);
+	return ret;
+}
+
 static int create_dyn_event(const char *raw_command)
 {
 	struct dyn_event_operations *ops;

kernel/trace/trace_dynevent.h +1 -0

index 936477a111d3..beee3f8d7544 100644
@@ -100,6 +100,7 @@ void *dyn_event_seq_next(struct seq_file *m, void *v, loff_t *pos);
 void dyn_event_seq_stop(struct seq_file *m, void *v);
 int dyn_events_release_all(struct dyn_event_operations *type);
 int dyn_event_release(const char *raw_command, struct dyn_event_operations *type);
+int dyn_event_create(const char *raw_command, struct dyn_event_operations *type);
 
 /*
  * for_each_dyn_event	-	iterate over the dyn_event list

kernel/trace/trace_kprobe.c +1 -1

index 2703b96d8990..3e5c47b6d7b2 100644
@@ -1089,7 +1089,7 @@ static int create_or_delete_trace_kprobe(const char *raw_command)
 	if (raw_command[0] == '-')
 		return dyn_event_release(raw_command, &trace_kprobe_ops);
 
-	ret = trace_kprobe_create(raw_command);
+	ret = dyn_event_create(raw_command, &trace_kprobe_ops);
 	return ret == -ECANCELED ? -EINVAL : ret;
 }
 

kernel/trace/trace_probe.c +9 -0

index 2eeecb6c95ee..424751cdf31f 100644
@@ -154,9 +154,12 @@ static const struct fetch_type *find_fetch_type(const char *type, unsigned long
 }
 
 static struct trace_probe_log trace_probe_log;
+extern struct mutex dyn_event_ops_mutex;
 
 void trace_probe_log_init(const char *subsystem, int argc, const char **argv)
 {
+	lockdep_assert_held(&dyn_event_ops_mutex);
+
 	trace_probe_log.subsystem = subsystem;
 	trace_probe_log.argc = argc;
 	trace_probe_log.argv = argv;

@@ -165,11 +168,15 @@ void trace_probe_log_init(const char *subsystem, int argc, const char **argv)
 
 void trace_probe_log_clear(void)
 {
+	lockdep_assert_held(&dyn_event_ops_mutex);
+
 	memset(&trace_probe_log, 0, sizeof(trace_probe_log));
 }
 
 void trace_probe_log_set_index(int index)
 {
+	lockdep_assert_held(&dyn_event_ops_mutex);
+
 	trace_probe_log.index = index;
 }
 

@@ -178,6 +185,8 @@ void __trace_probe_log_err(int offset, int err_type)
 	char *command, *p;
 	int i, len = 0, pos = 0;
 
+	lockdep_assert_held(&dyn_event_ops_mutex);
+
 	if (!trace_probe_log.argv)
 		return;
 

kernel/trace/trace_uprobe.c +1 -1

index 3386439ec9f6..35cf76c75dd7 100644
@@ -741,7 +741,7 @@ static int create_or_delete_trace_uprobe(const char *raw_command)
 	if (raw_command[0] == '-')
 		return dyn_event_release(raw_command, &trace_uprobe_ops);
 
-	ret = trace_uprobe_create(raw_command);
+	ret = dyn_event_create(raw_command, &trace_uprobe_ops);
 	return ret == -ECANCELED ? -EINVAL : ret;
 }
 

BTW, this fixes the problem introduced by commit ab105a4fb894 ("tracing: Use tracing error_log with probe events"). However, this patch can be applied after commit d262271d0483 ("tracing/dynevent: Delegate parsing to create function").

Thus, before that commit, we may need another way to fix this issue. (e.g. introduce a different mutex.) Anyway, to record the correct fixes;

Fixes ab105a4fb894 ("tracing: Use tracing error_log with probe events")