Re: [PATCH] ftrace: Add checking nr_subbufs to persistent ring buffer validation

[Vincent Donnefort <vdonnefort@google.com>]

On Thu, Sep 03, 2026 at 01:27:28PM -0400, Steven Rostedt wrote:
> From: Steven Rostedt <rostedt@goodmis.org>
> 
> Sashiko reported that the code was using meta->nr_subbufs without making
> sure that it matched the nr_pages + 1 on data that was assuming the two
> were the same.
> 
> Add a check to the persistent ring buffer validation code to make sure
> that the saved nr_subbufs matches what we expect.
> 
> Fixes: f5b95f1fa2ef3 ("ring-buffer: Validate the persistent meta data subbuf array")
> Reported-by: sashiko-bot@kernel.org
> Closes: https://lore.kernel.org/all/20260901164836.D962D1F000E9@smtp.kernel.org/
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Reviewed-by: Vincent Donnefort <vdonnefort@google.com>

> ---
>  kernel/trace/ring_buffer.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index ef66f726e2e2..748d4ae8badf 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -1869,6 +1869,11 @@ static bool rb_cpu_meta_valid(struct ring_buffer_cpu_meta *meta, int cpu,
>  		return false;
>  	}
>  
> +	if (meta->nr_subbufs != nr_pages + 1) {
> +		pr_info("Ring buffer boot meta [%d] invalid nr_subbufs\n", cpu);
> +		return false;
> +	}
> +
>  	buffers_start = meta->first_buffer;
>  	buffers_end = meta->first_buffer + (subbuf_size * meta->nr_subbufs);
>  
> -- 
> 2.53.0
>