Re: [PATCH] tracing: Add size check when printing trace_marker output

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

On 2023-12-12 08:44, Steven Rostedt wrote:
> From: "Steven Rostedt (Google)" <rostedt@goodmis.org>
> 
> If for some reason the trace_marker write does not have a nul byte for the
> string, it will overflow the print:

Does this result in leaking kernel memory to userspace ? If so, it
should state "Fixes..." and CC stable.

Thanks,

Mathieu

> 
>    trace_seq_printf(s, ": %s", field->buf);
> 
> The field->buf could be missing the nul byte. To prevent overflow, add the
> max size that the buf can be by using the event size and the field
> location.
> 
>    int max = iter->ent_size - offsetof(struct print_entry, buf);
> 
>    trace_seq_printf(s, ": %*s", max, field->buf);
> 
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> ---
>   kernel/trace/trace_output.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
> index d8b302d01083..e11fb8996286 100644
> --- a/kernel/trace/trace_output.c
> +++ b/kernel/trace/trace_output.c
> @@ -1587,11 +1587,12 @@ static enum print_line_t trace_print_print(struct trace_iterator *iter,
>   {
>   	struct print_entry *field;
>   	struct trace_seq *s = &iter->seq;
> +	int max = iter->ent_size - offsetof(struct print_entry, buf);
>   
>   	trace_assign_type(field, iter->ent);
>   
>   	seq_print_ip_sym(s, field->ip, flags);
> -	trace_seq_printf(s, ": %s", field->buf);
> +	trace_seq_printf(s, ": %*s", max, field->buf);
>   
>   	return trace_handle_return(s);
>   }
> @@ -1600,10 +1601,11 @@ static enum print_line_t trace_print_raw(struct trace_iterator *iter, int flags,
>   					 struct trace_event *event)
>   {
>   	struct print_entry *field;
> +	int max = iter->ent_size - offsetof(struct print_entry, buf);
>   
>   	trace_assign_type(field, iter->ent);
>   
> -	trace_seq_printf(&iter->seq, "# %lx %s", field->ip, field->buf);
> +	trace_seq_printf(&iter->seq, "# %lx %*s", field->ip, max, field->buf);
>   
>   	return trace_handle_return(&iter->seq);
>   }

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com