linux-kernel - Re: [PATCH V8 1/2] printk: remove tabular output for NULL pointer

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Message-ID: <1508993843.10651.22.camel@perches.com>
Date:   Wed, 25 Oct 2017 21:57:23 -0700
From:   Joe Perches <joe@...ches.com>
To:     "Tobin C. Harding" <me@...in.cc>,
        kernel-hardening@...ts.openwall.com
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Theodore Ts'o <tytso@....edu>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Tycho Andersen <tycho@...ker.com>,
        "Roberts, William C" <william.c.roberts@...el.com>,
        Tejun Heo <tj@...nel.org>,
        Jordan Glover <Golden_Miller83@...tonmail.ch>,
        Greg KH <gregkh@...uxfoundation.org>,
        Petr Mladek <pmladek@...e.com>,
        Ian Campbell <ijc@...lion.org.uk>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <wilal.deacon@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Chris Fries <cfries@...gle.com>,
        Dave Weinstein <olorin@...gle.com>,
        Daniel Micay <danielmicay@...il.com>,
        Djalal Harouni <tixxdz@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V8 1/2] printk: remove tabular output for NULL pointer

On Thu, 2017-10-26 at 13:53 +1100, Tobin C. Harding wrote:
> Currently pointer() checks for a NULL pointer argument and then if so
> attempts to print "(null)" with _some_ standard width. This width cannot
> correctly be ascertained here because many of the printk specifiers
> print pointers of varying widths.

I believe this is not a good change.
Only pointers without a <foo> extension call pointer()

> Remove the attempt to print NULL pointers with a correct width.

the correct width for a %p is the default width.
The correct width for %p<foo> is unknown.

> Signed-off-by: Tobin C. Harding <me@...in.cc>
> ---
>  lib/vsprintf.c | 9 +--------
>  1 file changed, 1 insertion(+), 8 deletions(-)
> 
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 86c3385b9eb3..16a587aed40e 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -1710,15 +1710,8 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
>  {
>  	const int default_width = 2 * sizeof(void *);
>  
> -	if (!ptr && *fmt != 'K') {
> -		/*
> -		 * Print (null) with the same width as a pointer so it makes
> -		 * tabular output look nice.
> -		 */
> -		if (spec.field_width == -1)
> -			spec.field_width = default_width;
> +	if (!ptr && *fmt != 'K')
>  		return string(buf, end, "(null)", spec);
> -	}
>  
>  	switch (*fmt) {
>  	case 'F':