[STABLE v5.15-v5.10] tracing/histograms: Verify event_call identity when updating synth_event refcount

[STABLE v5.15-v5.10] tracing/histograms: Verify event_call identity when updating synth_event refcount

[Lee Jones]

[ Upstream commit 3403d9bb27ebc3572bd048620746b4414e073bf9 ]

In event_hist_trigger_parse() and hist_unreg_all(), the histogram
registration and unregistration paths look up find_synth_event() using
trace_event_name(file->event_call) and adjust se->ref if a match is
found.

Because find_synth_event() only compares the event basename, registering
or removing a histogram on a non-synthetic trace event whose basename
matches a synthetic event erroneously modifies the synthetic event's
reference count.  If a histogram is registered on the non-synthetic
event before the synthetic event is created and removed afterwards,
se->ref is decremented without a matching increment, allowing the
synthetic event to be freed while an active histogram action still holds
a pointer to it.

Introduce find_synth_event_call() to verify that &se->call matches
file->event_call before adjusting se->ref.

Fixes: 4b147936fa50 ("tracing: Add support for 'synthetic' events")
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20261019120730.2342739-1-lee@kernel.org
Signed-off-by: Lee Jones <lee@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
[Lee: Context conflict in event_hist_trigger_func() - no functional change]
Signed-off-by: Lee Jones <lee@kernel.org>
---
 kernel/trace/trace_events_hist.c  | 11 +++--------
 kernel/trace/trace_events_synth.c | 10 ++++++++++
 kernel/trace/trace_synth.h        |  1 +
 3 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 223b38f9ac0e..c8e57b6e28fd 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -5797,7 +5797,6 @@ static void hist_unreg_all(struct trace_event_file *file)
 	struct event_trigger_data *test, *n;
 	struct hist_trigger_data *hist_data;
 	struct synth_event *se;
-	const char *se_name;
 
 	lockdep_assert_held(&event_mutex);
 
@@ -5810,8 +5809,7 @@ static void hist_unreg_all(struct trace_event_file *file)
 			list_del_rcu(&test->list);
 			trace_event_trigger_enable_disable(file, 0);
 
-			se_name = trace_event_name(file->event_call);
-			se = find_synth_event(se_name);
+			se = find_synth_event_call(file->event_call);
 			if (se)
 				se->ref--;
 
@@ -5834,7 +5832,6 @@ static int event_hist_trigger_func(struct event_command *cmd_ops,
 	struct event_trigger_ops *trigger_ops;
 	struct hist_trigger_data *hist_data;
 	struct synth_event *se;
-	const char *se_name;
 	bool remove = false;
 	char *trigger, *p;
 	int ret = 0;
@@ -5931,8 +5928,7 @@ static int event_hist_trigger_func(struct event_command *cmd_ops,
 		}
 
 		cmd_ops->unreg(glob+1, trigger_ops, trigger_data, file);
-		se_name = trace_event_name(file->event_call);
-		se = find_synth_event(se_name);
+		se = find_synth_event_call(file->event_call);
 		if (se)
 			se->ref--;
 		ret = 0;
@@ -5973,8 +5969,7 @@ static int event_hist_trigger_func(struct event_command *cmd_ops,
 	if (ret)
 		goto out_unreg;
 
-	se_name = trace_event_name(file->event_call);
-	se = find_synth_event(se_name);
+	se = find_synth_event_call(file->event_call);
 	if (se)
 		se->ref++;
 	/* Just return zero, not the number of registered triggers */
diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
index 62d146254f47..ba5647204d3e 100644
--- a/kernel/trace/trace_events_synth.c
+++ b/kernel/trace/trace_events_synth.c
@@ -848,6 +848,16 @@ struct synth_event *find_synth_event(const char *name)
 	return NULL;
 }
 
+struct synth_event *find_synth_event_call(struct trace_event_call *call)
+{
+	struct synth_event *se;
+	const char *name;
+
+	name = trace_event_name(call);
+	se = find_synth_event(name);
+	return se && &se->call == call ? se : NULL;
+}
+
 static struct trace_event_fields synth_event_fields_array[] = {
 	{ .type = TRACE_FUNCTION_TYPE,
 	  .define_fields = synth_event_define_fields },
diff --git a/kernel/trace/trace_synth.h b/kernel/trace/trace_synth.h
index 43f6fb6078db..d4ebf01b7049 100644
--- a/kernel/trace/trace_synth.h
+++ b/kernel/trace/trace_synth.h
@@ -37,5 +37,6 @@ struct synth_event {
 };
 
 extern struct synth_event *find_synth_event(const char *name);
+extern struct synth_event *find_synth_event_call(struct trace_event_call *call);
 
 #endif /* __TRACE_SYNTH_H */
-- 
2.56.0.506.g506a7eabc5-goog

Re: [STABLE v5.15-v5.10] tracing/histograms: Verify event_call identity when updating synth_event refcount

[Sasha Levin]

> tracing/histograms: Verify event_call identity when updating synth_event refcount

Queued for 5.15 and 5.10, thanks.

-- 
Thanks,
Sasha