[PATCH] tracing: Fix race where eprobes can be called before the event

[PATCH] tracing: Fix race where eprobes can be called before the event

[Steven Rostedt]

From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

The flag that tells the event to call its triggers after reading the event
is set for eprobes after the eprobe is enabled. This leads to a race where
the eprobe may be triggered at the beginning of the event where the record
information is NULL. The eprobe then dereferences the NULL record causing
a NULL kernel pointer bug.

Test for a NULL record to keep this from happening.

Link: https://lore.kernel.org/linux-trace-kernel/20221116192552.1066630-1-rafaelmendsr@gmail.com/

Cc: stable@vger.kernel.org
Fixes: 7491e2c442781 ("tracing: Add a probe that attaches to trace events")
Reported-by: Rafael Mendonca <rafaelmendsr@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/trace_eprobe.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/trace/trace_eprobe.c b/kernel/trace/trace_eprobe.c
index 5dd0617e5df6..6b31b74954d9 100644
--- a/kernel/trace/trace_eprobe.c
+++ b/kernel/trace/trace_eprobe.c
@@ -563,6 +563,9 @@ static void eprobe_trigger_func(struct event_trigger_data *data,
 {
 	struct eprobe_data *edata = data->private_data;
 
+	if (unlikely(!rec))
+		return;
+
 	__eprobe_trace_func(edata, rec);
 }
 
-- 
2.35.1

Re: [PATCH] tracing: Fix race where eprobes can be called before the event

[Masami Hiramatsu]

On Thu, 17 Nov 2022 21:42:49 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> From: "Steven Rostedt (Google)" <rostedt@goodmis.org>
> 
> The flag that tells the event to call its triggers after reading the event
> is set for eprobes after the eprobe is enabled. This leads to a race where
> the eprobe may be triggered at the beginning of the event where the record
> information is NULL. The eprobe then dereferences the NULL record causing
> a NULL kernel pointer bug.
> 
> Test for a NULL record to keep this from happening.
> 
> Link: https://lore.kernel.org/linux-trace-kernel/20221116192552.1066630-1-rafaelmendsr@gmail.com/

This looks good to me.

Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

BTW, would other trigger callbacks also need to add similar checks?

Thank you,

> 
> Cc: stable@vger.kernel.org
> Fixes: 7491e2c442781 ("tracing: Add a probe that attaches to trace events")
> Reported-by: Rafael Mendonca <rafaelmendsr@gmail.com>
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> ---
>  kernel/trace/trace_eprobe.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/trace/trace_eprobe.c b/kernel/trace/trace_eprobe.c
> index 5dd0617e5df6..6b31b74954d9 100644
> --- a/kernel/trace/trace_eprobe.c
> +++ b/kernel/trace/trace_eprobe.c
> @@ -563,6 +563,9 @@ static void eprobe_trigger_func(struct event_trigger_data *data,
>  {
>  	struct eprobe_data *edata = data->private_data;
>  
> +	if (unlikely(!rec))
> +		return;
> +
>  	__eprobe_trace_func(edata, rec);
>  }
>  
> -- 
> 2.35.1
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>

Re: [PATCH] tracing: Fix race where eprobes can be called before the event

[Steven Rostedt]

On Fri, 18 Nov 2022 21:18:09 +0900
Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:

> This looks good to me.
> 
> Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> 
> BTW, would other trigger callbacks also need to add similar checks?

I just checked, and yes, I think that histograms (the only other trigger
that has EVENT_CMD_FL_NEEDS_REC set) has the same issue, and requires:

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 087c19548049..1c82478e8dff 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -5143,6 +5143,9 @@ static void event_hist_trigger(struct event_trigger_data *data,
 	void *key = NULL;
 	unsigned int i;
 
+	if (unlikely(!rbe))
+		return;
+
 	memset(compound_key, 0, hist_data->key_size);
 
 	for_each_hist_key_field(i, hist_data) {


I'll add that next.

-- Steve