[PATCH v4] tracing: Fix use-after-free freeing trigger private data
From: David Carlier <hidden>
Date: 2026-07-24 03:05:28
Also in:
lkml
Subsystem:
the rest, tracing · Maintainers:
Linus Torvalds, Steven Rostedt, Masami Hiramatsu
Commit 61d445af0a7c ("tracing: Add bulk garbage collection of freeing
event_trigger_data") moved the kfree() of event_trigger_data to a kthread
that runs tracepoint_synchronize_unregister() before freeing. That removed
the synchronization the trigger .free callbacks used to get implicitly and
inline from trigger_data_free().
event_hist_trigger_free(), event_hist_trigger_named_free() and
event_enable_trigger_free() free their satellite data (hist_data, cmd_ops,
enable_data) right after trigger_data_free() returns. With the
synchronization now deferred to the kthread, a concurrent tracepoint
handler can still reach that data through the list_del_rcu()'d trigger,
causing a use-after-free.
The histogram teardown must stay synchronous: remove_hist_vars() and
unregister_field_var_hists() have to detach a synthetic event from the
histogram before the trigger-removal write returns, otherwise a following
command races in and the synthetic-event removal fails with -EBUSY, as the
trigger-synthetic-eprobe.tc selftest catches. Make those callbacks wait
with the correct barrier - tracepoint_synchronize_unregister(), matching
the free kthread - before freeing.
The enable trigger has no such synchronous requirement, and a blocking
synchronize there would re-serialize the path that commit deliberately
deferred. Give it an optional private_data_free() callback that the free
kthread runs after its grace period, and free enable_data from there.
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Fixes: 61d445af0a7c ("tracing: Add bulk garbage collection of freeing event_trigger_data")
Signed-off-by: David Carlier <redacted>
---
kernel/trace/trace.h | 1 +
kernel/trace/trace_events_hist.c | 2 ++
kernel/trace/trace_events_trigger.c | 18 +++++++++++++++---
3 files changed, 18 insertions(+), 3 deletions(-)
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 80fe152af1dd..bf77331f56a4 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h@@ -1941,6 +1941,7 @@ struct event_trigger_data { struct list_head named_list; struct event_trigger_data *named_data; struct llist_node llist; + void (*private_data_free)(struct event_trigger_data *data); }; /* Avoid typos */
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 82ce492ab268..58d28cd1afa3 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c@@ -6349,6 +6349,7 @@ static void event_hist_trigger_free(struct event_trigger_data *data) trigger_data_free(data); + tracepoint_synchronize_unregister(); remove_hist_vars(hist_data); unregister_field_var_hists(hist_data);
@@ -6388,6 +6389,7 @@ static void event_hist_trigger_named_free(struct event_trigger_data *data) del_named_trigger(data); trigger_data_free(data); + tracepoint_synchronize_unregister(); kfree(cmd_ops); } }
diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
index 655db2e82513..46e60b70a4bb 100644
--- a/kernel/trace/trace_events_trigger.c
+++ b/kernel/trace/trace_events_trigger.c@@ -38,6 +38,13 @@ static void trigger_create_kthread_locked(void) } } +static void trigger_data_free_one(struct event_trigger_data *data) +{ + if (data->private_data_free) + data->private_data_free(data); + kfree(data); +} + static void trigger_data_free_queued_locked(void) { struct event_trigger_data *data, *tmp;
@@ -52,7 +59,7 @@ static void trigger_data_free_queued_locked(void) tracepoint_synchronize_unregister(); llist_for_each_entry_safe(data, tmp, llnodes, llist) - kfree(data); + trigger_data_free_one(data); } /* Bulk garbage collection of event_trigger_data elements */
@@ -75,7 +82,7 @@ static int trigger_kthread_fn(void *ignore) tracepoint_synchronize_unregister(); llist_for_each_entry_safe(data, tmp, llnodes, llist) - kfree(data); + trigger_data_free_one(data); } return 0;
@@ -1717,6 +1724,11 @@ int event_enable_trigger_print(struct seq_file *m, return 0; } +static void enable_trigger_private_data_free(struct event_trigger_data *data) +{ + kfree(data->private_data); +} + void event_enable_trigger_free(struct event_trigger_data *data) { struct enable_trigger_data *enable_data = data->private_data;
@@ -1728,9 +1740,9 @@ void event_enable_trigger_free(struct event_trigger_data *data) if (!data->ref) { /* Remove the SOFT_MODE flag */ trace_event_enable_disable(enable_data->file, 0, 1); + data->private_data_free = enable_trigger_private_data_free; trace_event_put_ref(enable_data->file->event_call); trigger_data_free(data); - kfree(enable_data); } }
--
2.53.0