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

[Google]

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

> From: "Steven Rostedt (Google)" <rostedt@xxxxxxxxxxx>
> 
> 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@xxxxxxxxx/

This looks good to me.

Acked-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

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

Thank you,

> 
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 7491e2c442781 ("tracing: Add a probe that attaches to trace events")
> Reported-by: Rafael Mendonca <rafaelmendsr@xxxxxxxxx>
> Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
> ---
>  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@xxxxxxxxxx>