linux-kernel - Re: [PATCH v4 4/9] vsprintf: Consolidate handling of unknown pointer specifiers

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Message-ID: <1523111200.21176.416.camel@linux.intel.com>
Date:   Sat, 07 Apr 2018 17:26:40 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Petr Mladek <pmladek@...e.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        "Tobin C . Harding" <me@...in.cc>, Joe Perches <joe@...ches.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.cz>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 4/9] vsprintf: Consolidate handling of unknown
 pointer specifiers

On Wed, 2018-04-04 at 10:58 +0200, Petr Mladek wrote:
> There are few printk formats that make sense only with two or more
> specifiers. Also some specifiers make sense only when a kernel feature
> is enabled.
> 
> The handling of unknown specifiers is strange, inconsistent, and
> even leaking the address. For example, netdev_bits() prints the
> non-hashed pointer value or clock() prints "(null)".
> 
> The best solution seems to be in flags_string(). It does not print any
> misleading value. Instead it calls WARN_ONCE() describing the unknown
> specifier. Therefore it clearly shows the problem and helps to find
> it.
> 
> Note that WARN_ONCE() used to cause recursive printk(). But it is safe
> now because vscnprintf() is called in printk_safe context from
> vprintk_emit().
> 

> -	if (!IS_ENABLED(CONFIG_HAVE_CLK) || !clk)
> +	if (!IS_ENABLED(CONFIG_HAVE_CLK)) {
> +		WARN_ONCE(1, "Unsupported pointer format specifier:
> %%pC\n");
> +		return buf;
> +	}
> +
> +	if (!clk)
>  		return string(buf, end, NULL, spec);

This change collides with my patch series. Can you elaborate what your
thoughts are about my patches? Are you going incorporate them to your
series? Should I send them independently?

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy