linux-hardening - Re: [PATCH] seq_buf: Introduce DECLARE_SEQ_BUF and seq_buf

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Date: Thu, 26 Oct 2023 10:54:26 -0700
From: Kees Cook <keescook@...omium.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: "Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Christoph Hellwig <hch@....de>,
	Justin Stitt <justinstitt@...gle.com>,
	Kent Overstreet <kent.overstreet@...ux.dev>,
	Petr Mladek <pmladek@...e.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Arnd Bergmann <arnd@...db.de>, Jonathan Corbet <corbet@....net>,
	Yun Zhou <yun.zhou@...driver.com>,
	Jacob Keller <jacob.e.keller@...el.com>,
	Zhen Lei <thunder.leizhen@...wei.com>,
	linux-trace-kernel@...r.kernel.org,
	Yosry Ahmed <yosryahmed@...gle.com>, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH] seq_buf: Introduce DECLARE_SEQ_BUF and seq_buf_cstr()

On Thu, Oct 26, 2023 at 01:38:50PM -0400, Steven Rostedt wrote:
> On Thu, 26 Oct 2023 10:07:28 -0700
> Kees Cook <keescook@...omium.org> wrote:
> 
> > Solve two ergonomic issues with struct seq_buf:
> 
> "ergonomic"? Does it cause carpal tunnel? ;-)
> 
> > 
> > 1) Too much boilerplate is required to initialize:
> > 
> > 	struct seq_buf s;
> > 	char buf[32];
> > 
> > 	seq_buf_init(s, buf, sizeof(buf));
> > 
> > Instead, we can build this directly on the stack. Provide
> > DECLARE_SEQ_BUF() macro to do this:
> > 
> > 	DECLARE_SEQ_BUF(s, 32);
> > 
> > 2) %NUL termination is fragile and requires 2 steps to get a valid
> >    C String (and is a layering violation exposing the "internals" of
> >    seq_buf):
> > 
> > 	seq_buf_terminate(s);
> > 	do_something(s->buffer);
> > 
> > Instead, we can just return s->buffer direction after terminating it
> > in refactored seq_buf_terminate(), now known as seq_buf_cstr():
> > 
> > 	do_soemthing(seq_buf_cstr(s));
> 
> Do we really need to call it _cstr? Why not just have seq_buf_str() ?
> 
> I mean, this is C, do we need to state that in the name too?

I'm fine either way. I did that just to make the distinction between our
length-managed string of characters interface (seq_buf), and the
%NUL-terminated string of characters (traditionally called "C String" in
other languages). And it was still shorter than "seq_buf_terminate(s);
s->buffer" ;)

> BTW, I'm perfectly fine with this change, just the naming I have issues
> with.

Cool; thanks for looking at it!

-- 
Kees Cook