linux-kernel - Re: [PATCH 5/9] Remove unused %*pE[achnops] formats

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Date:   Thu, 5 Sep 2019 14:34:56 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "J. Bruce Fields" <bfields@...hat.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/9] Remove unused %*pE[achnops] formats

On Thu, Sep 05, 2019 at 03:44:29PM -0400, J. Bruce Fields wrote:
> From: "J. Bruce Fields" <bfields@...hat.com>
> 
> The [achnops] are confusing, and in practice the only one anyone seems
> to need is the bare %*pE.
> 
> I think some set of modifiers here might actually be useful, but the
> ones we have are confusing and unused, so let's just toss these out and
> then rethink what we might want to add back later.
> 
> Signed-off-by: J. Bruce Fields <bfields@...hat.com>

Acked-by: Kees Cook <keescook@...omium.org>

Typo below...

> ---
>  Documentation/core-api/printk-formats.rst | 23 ++---------
>  lib/vsprintf.c                            | 50 ++---------------------
>  2 files changed, 7 insertions(+), 66 deletions(-)
> 
> diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
> index c6224d039bcb..4f9d20dfb342 100644
> --- a/Documentation/core-api/printk-formats.rst
> +++ b/Documentation/core-api/printk-formats.rst
> @@ -180,35 +180,20 @@ Raw buffer as an escaped string
>  
>  ::
>  
> -	%*pE[achnops]
> +	%*pE
>  
>  For printing raw buffer as an escaped string. For the following buffer::
>  
>  		1b 62 20 5c 43 07 22 90 0d 5d
>  
> -A few examples show how the conversion would be done (excluding surrounding
> +An example shows how the conversion would be done (excluding surrounding
>  quotes)::
>  
>  		%*pE		"\eb \C\a"\220\r]"
> -		%*pEhp		"\x1bb \C\x07"\x90\x0d]"
> -		%*pEa		"\e\142\040\\\103\a\042\220\r\135"
>  
> -The conversion rules are applied according to an optional combination
> -of flags (see :c:func:`string_escape_mem` kernel documentation for the
> -details):
> +See :c:func:`string_escape_mem` kernel documentation for the details.
>  
> -	- a - ESCAPE_ANY
> -	- c - ESCAPE_SPECIAL
> -	- h - ESCAPE_HEX
> -	- n - ESCAPE_NULL
> -	- o - ESCAPE_OCTAL
> -	- p - ESCAPE_NP
> -	- s - ESCAPE_SPACE
> -
> -By default ESCAPE_ANY_NP is used.
> -
> -ESCAPE_ANY_NP is the sane choice for many cases, in particularly for
> -printing SSIDs.
> +This is used, for example, for printing SSIDs.
>  
>  If field width is omitted then 1 byte only will be escaped.
>  
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index b0967cf17137..5522d2a052e1 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -1537,9 +1537,6 @@ static noinline_for_stack
>  char *escaped_string(char *buf, char *end, u8 *addr, struct printf_spec spec,
>  		     const char *fmt)
>  {
> -	bool found = true;
> -	int count = 1;
> -	unsigned int flags = 0;
>  	int len;
>  
>  	if (spec.field_width == 0)
> @@ -1548,38 +1545,6 @@ char *escaped_string(char *buf, char *end, u8 *addr, struct printf_spec spec,
>  	if (check_pointer(&buf, end, addr, spec))
>  		return buf;
>  
> -	do {
> -		switch (fmt[count++]) {
> -		case 'a':
> -			flags |= ESCAPE_ANY;
> -			break;
> -		case 'c':
> -			flags |= ESCAPE_SPECIAL;
> -			break;
> -		case 'h':
> -			flags |= ESCAPE_HEX;
> -			break;
> -		case 'n':
> -			flags |= ESCAPE_NULL;
> -			break;
> -		case 'o':
> -			flags |= ESCAPE_OCTAL;
> -			break;
> -		case 'p':
> -			flags |= ESCAPE_NP;
> -			break;
> -		case 's':
> -			flags |= ESCAPE_SPACE;
> -			break;
> -		default:
> -			found = false;
> -			break;
> -		}
> -	} while (found);
> -
> -	if (!flags)
> -		flags = ESCAPE_ANY_NP;
> -
>  	len = spec.field_width < 0 ? 1 : spec.field_width;
>  
>  	/*
> @@ -1587,7 +1552,8 @@ char *escaped_string(char *buf, char *end, u8 *addr, struct printf_spec spec,
>  	 * the given buffer, and returns the total size of the output
>  	 * had the buffer been big enough.
>  	 */
> -	buf += string_escape_mem(addr, len, buf, buf < end ? end - buf : 0, flags, NULL);
> +	buf += string_escape_mem(addr, len, buf, buf < end ? end - buf : 0,
> +				 ESCAPE_ANY_NP, NULL);
>  
>  	return buf;
>  }
> @@ -2038,17 +2004,7 @@ static char *kobject_string(char *buf, char *end, void *ptr,
>   * - '[Ii][4S][hnbl]' IPv4 addresses in host, network, big or little endian order
>   * - 'I[6S]c' for IPv6 addresses printed as specified by
>   *       http://tools.ietf.org/html/rfc5952
> - * - 'E[achnops]' For an escaped buffer, where rules are defined by combination
> - *                of the following flags (see string_escape_mem() for the
> - *                details):
> - *                  a - ESCAPE_ANY
> - *                  c - ESCAPE_SPECIAL
> - *                  h - ESCAPE_HEX
> - *                  n - ESCAPE_NULL
> - *                  o - ESCAPE_OCTAL
> - *                  p - ESCAPE_NP
> - *                  s - ESCAPE_SPACE
> - *                By default ESCAPE_ANY_NP is used.
> + * - 'E[achnops]' For an escaped buffer (see string_escape_mem()

This line should be like this; no more suboptions and add missed final ")":

 * - 'E' For an escaped buffer (see string_escape_mem())

-Kees

>   * - 'U' For a 16 byte UUID/GUID, it prints the UUID/GUID in the form
>   *       "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx"
>   *       Options for %pU are:
> -- 
> 2.21.0
> 

-- 
Kees Cook