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[188.141.5.72]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-47f85c531basm20280576f8f.19.2026.07.23.20.05.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Jul 2026 20:05:26 -0700 (PDT) From: David Carlier To: Steven Rostedt , Masami Hiramatsu Cc: Mathieu Desnoyers , linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org, David Carlier Subject: [PATCH v4] tracing: Fix use-after-free freeing trigger private data Date: Fri, 24 Jul 2026 04:05:17 +0100 Message-ID: <20260724030523.19081-1-devnexen@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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) Suggested-by: Steven Rostedt Fixes: 61d445af0a7c ("tracing: Add bulk garbage collection of freeing event_trigger_data") Signed-off-by: David Carlier --- 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