Re: [PATCH] tracing: ring-buffer: Fix to check event length before using

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

I found another problem. Let me make a series for fixing issues.

Thanks,

On Mon, 16 Feb 2026 18:30:15 +0900
"Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:

> From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> 
> Check the event length before adding it for accessing next index in
> rb_read_data_buffer(). Since this function is used for validating
> possibly broken ring buffers, the length of the event could be broken.
> In that case, the new event (e + len) can point a wrong address.
> To avoid invalid memory access at boot, check whether the length of
> each event is in the possible range before using it.
> 
> Fixes: 5f3b6e839f3c ("ring-buffer: Validate boot range memory events")
> Cc: stable@vger.kernel.org
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> ---
>  kernel/trace/ring_buffer.c |    6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index 630221b00838..1ef17d6fd824 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -1848,6 +1848,7 @@ static int rb_read_data_buffer(struct buffer_data_page *dpage, int tail, int cpu
>  	struct ring_buffer_event *event;
>  	u64 ts, delta;
>  	int events = 0;
> +	int len;
>  	int e;
>  
>  	*delta_ptr = 0;
> @@ -1855,9 +1856,12 @@ static int rb_read_data_buffer(struct buffer_data_page *dpage, int tail, int cpu
>  
>  	ts = dpage->time_stamp;
>  
> -	for (e = 0; e < tail; e += rb_event_length(event)) {
> +	for (e = 0; e < tail; e += len) {
>  
>  		event = (struct ring_buffer_event *)(dpage->data + e);
> +		len = rb_event_length(event);
> +		if (len <= 0 || len > tail - e)
> +			return -1;
>  
>  		switch (event->type_len) {
>  
> 


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