linux-kernel - Re: [PATCH] tracing: Add size check when printing trace

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Message-Id: <20231213074746.cd2dbd703bd19fe791c5d44a@kernel.org>
Date:   Wed, 13 Dec 2023 07:47:46 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux Trace Kernel <linux-trace-kernel@...r.kernel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH] tracing: Add size check when printing trace_marker
 output

On Tue, 12 Dec 2023 08:44:44 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> From: "Steven Rostedt (Google)" <rostedt@...dmis.org>
> 
> If for some reason the trace_marker write does not have a nul byte for the
> string, it will overflow the print:
> 
>   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);
> 

This looks good to me.

Reviewed-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>

Thanks!

> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.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);
>  }
> -- 
> 2.42.0
> 


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