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

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Message-ID: <20231212221010.70c84d2d@gandalf.local.home>
Date:   Tue, 12 Dec 2023 22:10:10 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     LKML <linux-kernel@...r.kernel.org>,
        Linux Trace Kernel <linux-trace-kernel@...r.kernel.org>
Cc:     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);

Bah, this needs to be:

   trace_seq_printf(s, ": %.*s", max, field->buf);

Note the '.' between % and *. Otherwise it right aligns the output.

This did fail the selftest for trace_printk(), but I modified the new one
to add " *" to accommodate it :-p

Sending out v2.

-- Steve