From: Tengda Wu wutengda@huaweicloud.com

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-QzVM06... Reported-by: Kairui Song kasong@tencent.com Signed-off-by: Tengda Wu wutengda@huaweicloud.com Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.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(-)

diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c index ed61ff719aa4..2f077d4158e5 100644 --- a/kernel/trace/trace_functions_graph.c +++ b/kernel/trace/trace_functions_graph.c @@ -1611,6 +1611,7 @@ void graph_trace_close(struct trace_iterator *iter) if (data) { free_percpu(data->cpu_data); kfree(data); + iter->private = NULL; } }

diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c index c8bfa7310a91..40c39e946940 100644 --- a/kernel/trace/trace_irqsoff.c +++ b/kernel/trace/trace_irqsoff.c @@ -250,8 +250,6 @@ static void irqsoff_trace_open(struct trace_iterator *iter) { if (is_graph(iter->tr)) graph_trace_open(iter); - else - iter->private = NULL; }

static void irqsoff_trace_close(struct trace_iterator *iter) diff --git a/kernel/trace/trace_sched_wakeup.c b/kernel/trace/trace_sched_wakeup.c index c9ba4259e03e..a0db3404f7f7 100644 --- a/kernel/trace/trace_sched_wakeup.c +++ b/kernel/trace/trace_sched_wakeup.c @@ -188,8 +188,6 @@ static void wakeup_trace_open(struct trace_iterator *iter) { if (is_graph(iter->tr)) graph_trace_open(iter); - else - iter->private = NULL; }

static void wakeup_trace_close(struct trace_iterator *iter)