linux-hardening - Re: [PATCH v2] seq_buf: Introduce DECLARE_SEQ_BUF and seq_buf

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Message-ID: <20231027045451.GA7838@lst.de>
Date: Fri, 27 Oct 2023 06:54:51 +0200
From: Christoph Hellwig <hch@....de>
To: Kees Cook <keescook@...omium.org>
Cc: Steven Rostedt <rostedt@...dmis.org>,
	"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 v2] seq_buf: Introduce DECLARE_SEQ_BUF and seq_buf_str()

On Thu, Oct 26, 2023 at 12:40:37PM -0700, Kees Cook wrote:
> Solve two ergonomic issues with struct seq_buf;
> 
> 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);

DECLARE_SEQ_BUF_ONSTACK maybe?  But otherwise this looks like a good
concept.

> Instead, we can just return s->buffer direction after terminating it
> in refactored seq_buf_terminate(), now known as seq_buf_str():
> 
> 	do_soemthing(seq_buf_str(s));

Looks good.  Btw, one typical do_something would be printing it,
so adding a format specifier that's using this helper would also
probably be very useful.