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

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Date:   Mon, 9 Apr 2018 15:50:28 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        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 Sat 2018-04-07 17:26:40, Andy Shevchenko wrote:
> 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?

Good question. I think that the best solution will be that I go
over your patchset and just add all valid ones into printk.git
for-4.18. Then I will base v5 of this patchset on top of it.

I should have done this earlier. But I did not expect that long
way for the access-check stuff. We originally planned to
do the access check first, see
https://lkml.kernel.org/r/1520000254.10722.389.camel@linux.intel.com
But the access check patchset still need some love, so it makes
sense to switch the order.

Best Regards,
Petr