tracing: Fix use-after-free in print_graph_function_flags during tracer switching

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>

diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index ed61ff719aa4b01834a2e28d6e987a8bb2182191..2f077d4158e5f6cc5f320a611baf67b89948b615 100644 (file)
--- 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 c8bfa7310a91d282746ddd125d3f505b95ea16a6..40c39e94694069d7c43ee49447fa4909c997468e 100644 (file)
--- 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 c9ba4259e03e9162cd66fc280180a03a63b14ad8..a0db3404f7f75fc7d81a75779b3009b54cf4d0cf 100644 (file)
--- 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)