[PATCH 5.4 152/154] tracing: Fix use-after-free in print_graph_function_flags during tracer switching

Greg Kroah-Hartman
2025-04-08T12:09:08Z

From: Tengda Wu <wutengda@huaweicloud.com>

commit 7f81f27b1093e4895e87b74143c59c055c3b1906 upstream.

Kairui reported a UAF issue in print_graph_function_flags() during
ftrace stress testing [1]. This issue can be reproduced if puting a
'mdelay(10)' after 'mutex_unlock(&trace_types_lock)' in s_start(),
and executing the following script:

$ echo function_graph > current_tracer
$ cat trace > /dev/null &
$ sleep 5 # Ensure the 'cat' reaches the 'mdelay(10)' point
$ echo timerlat > current_tracer

The root cause lies in the two calls to print_graph_function_flags
within print_trace_line during each s_show():

* One through 'iter->trace->print_line()';
* Another through 'event->funcs->trace()', which is hidden in
print_trace_fmt() before print_trace_line returns.

Tracer switching only updates the former, while the latter continues
to use the print_line function of the old tracer, which in the script
above is print_graph_function_flags.

Moreover, when switching from the 'function_graph' tracer to the
'timerlat' tracer, s_start only calls graph_trace_close of the
'function_graph' tracer to free 'iter->private', but does not set
it to NULL. This provides an opportunity for 'event->funcs->trace()'
to use an invalid 'iter->private'.

To fix this issue, set 'iter->private' to NULL immediately after
freeing it in graph_trace_close(), ensuring that an invalid pointer
is not passed to other tracers. Additionally, clean up the unnecessary
'iter->private = NULL' during each 'cat trace' when using wakeup and
irqsoff tracers.

[1] https://lore.kernel.org/all/20231112150030.84609-1-ryncsn@gmail.com/

Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Zheng Yejian <zhengyejian1@huawei.com>
Link: https://lore.kernel.org/20250320122137.23635-1-wutengda@huaweicloud.com
Fixes: eecb91b9f98d ("tracing: Fix memleak due to race between current_tracer and trace")
Closes: https://lore.kernel.org/all/CAMgjq7BW79KDSCyp+tZHjShSzHsScSiJxn5ffskp-QzVM06fxw@mail.gmail.com/
Reported-by: Kairui Song <kasong@tencent.com>
Signed-off-by: Tengda Wu <wutengda@huaweicloud.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/trace/trace_functions_graph.c | 1 +
kernel/trace/trace_irqsoff.c | 2 --
kernel/trace/trace_sched_wakeup.c | 2 --
3 files changed, 1 insertion(+), 4 deletions(-)

--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -1246,6 +1246,7 @@ void graph_trace_close(struct trace_iter
if (data) {
free_percpu(data->cpu_data);
kfree(data);
+ iter->private = NULL;
}
}

--- a/kernel/trace/trace_irqsoff.c
+++ b/kernel/trace/trace_irqsoff.c
@@ -228,8 +228,6 @@ static void irqsoff_trace_open(struct tr
{
if (is_graph(iter->tr))
graph_trace_open(iter);
- else
- iter->private = NULL;
}

static void irqsoff_trace_close(struct trace_iterator *iter)
--- a/kernel/trace/trace_sched_wakeup.c
+++ b/kernel/trace/trace_sched_wakeup.c
@@ -171,8 +171,6 @@ static void wakeup_trace_open(struct tra
{
if (is_graph(iter->tr))
graph_trace_open(iter);
- else
- iter->private = NULL;
}

static void wakeup_trace_close(struct trace_iterator *iter)