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From: Petr Mladek <pmladek@suse.com>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	"Tobin C . Harding" <me@tobin.cc>, Joe Perches <joe@perches.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Michal Hocko <mhocko@suse.cz>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 09/11] vsprintf: Prevent crash when dereferencing invalid pointers
Date: Fri, 27 Apr 2018 14:47:21 +0200	[thread overview]
Message-ID: <20180427124721.z2vrsrlohxzyv6vh@pathway.suse.cz> (raw)
In-Reply-To: <1524669054.21176.566.camel@linux.intel.com>

On Wed 2018-04-25 18:10:54, Andy Shevchenko wrote:
> On Wed, 2018-04-25 at 13:12 +0200, Petr Mladek wrote:
> > We already prevent crash when dereferencing some obviously broken
> > pointers. But the handling is not consistent. Sometimes we print
> > "(null)"
> > only for pure NULL pointer, sometimes for pointers in the first
> > page and sometimes also for pointers in the last page (error codes).
> > 
> > Note that printk() call this code under logbuf_lock. Any recursive
> > printks are redirected to the printk_safe implementation and the
> > messages
> > are stored into per-CPU buffers. These buffers might be eventually
> > flushed
> > in printk_safe_flush_on_panic() but it is not guaranteed.
> 
> > +static const char *check_pointer_access(const void *ptr)
> > +{
> > +	char byte;
> > +
> > +	if (!ptr)
> > +		return "(null)";
> > +
> > +	if (probe_kernel_address(ptr, byte))
> > +		return "(efault)";
> > +
> > +	return NULL;
> > +}
> > +
> > +static bool valid_pointer_access(char **buf, char *end, const void
> > *ptr,
> > +				 struct printf_spec spec)
> > +{
> > +	const char *err_msg;
> > +
> > +	err_msg = check_pointer_access(ptr);
> > +	if (err_msg) {
> > +		*buf = valid_string(*buf, end, err_msg, spec);
> > +		return false;
> > +	}
> > +
> > +	return true;
> > +}
> 
> I would preserve similar style of buf pointer handling, i.e.
> 
> static char *valid_pointer_access(char **buf, char *end,
> 				  const void *ptr, struct printf_spec spec)
> {
> 	const char *err_msg;
> 
> 	err_msg = check_pointer_access(ptr);
> 	if (err_msg)
> 		return = valid_string(*buf, end, err_msg, spec);
> 
> 	return NULL;
> }

Heh, I actually started with exactly this code. But it caused confusion.
The name suggests that it should return true on success and NULL
is false:

	if (!valid_pointer_access())
		return err;

Any better naming/code is welcome.

Best Reagrds,
Petr

  parent reply	other threads:[~2018-04-27 12:47 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-25 11:12 [PATCH v5 00/11] vsprintf: Prevent silent crashes and consolidate error handling Petr Mladek
2018-04-25 11:12 ` [PATCH v5 01/11] vsprintf: Shuffle misc pointer to string functions Petr Mladek
2018-04-25 14:57   ` Andy Shevchenko
2018-04-25 11:12 ` [PATCH v5 02/11] vsprintf: Add missing const ptr qualifier to prt_to_id() Petr Mladek
2018-04-25 14:57   ` Andy Shevchenko
2018-04-25 11:12 ` [PATCH v5 03/11] vsprintf: Consistent %pK handling for kptr_restrict == 0 Petr Mladek
2018-04-25 14:58   ` Andy Shevchenko
2018-04-25 11:12 ` [PATCH v5 04/11] vsprintf: Do not check address of well-known strings Petr Mladek
2018-04-25 11:44   ` Andy Shevchenko
2018-04-25 11:12 ` [PATCH v5 05/11] vsprintf: Consolidate handling of unknown pointer specifiers Petr Mladek
2018-04-25 13:08   ` Andy Shevchenko
2018-04-25 11:12 ` [PATCH v5 06/11] vsprintf: Factor out %p[iI] handler as ip_addr_string() Petr Mladek
2018-04-25 13:11   ` Andy Shevchenko
2018-04-25 11:12 ` [PATCH v5 07/11] vsprintf: Factor out %pV handler as va_format() Petr Mladek
2018-04-25 14:56   ` Andy Shevchenko
2018-04-25 11:12 ` [PATCH v5 08/11] vsprintf: Factor out %pO handler as kobject_string() Petr Mladek
2018-04-25 15:01   ` Andy Shevchenko
2018-04-25 11:12 ` [PATCH v5 09/11] vsprintf: Prevent crash when dereferencing invalid pointers Petr Mladek
2018-04-25 15:10   ` Andy Shevchenko
2018-04-25 15:32     ` Andy Shevchenko
2018-04-27 12:47     ` Petr Mladek [this message]
2018-05-03 11:55       ` Andy Shevchenko
2018-04-26 21:46   ` kbuild test robot
2018-04-25 11:12 ` [PATCH v5 10/11] vsprintf: WARN() on invalid pointer access Petr Mladek
2018-04-25 12:43   ` Rasmus Villemoes
2018-04-26  1:28   ` Sergey Senozhatsky
2018-04-27 12:37     ` Petr Mladek
2018-04-25 11:12 ` [PATCH v5 11/11] vsprintf: Avoid confusion between invalid address and value Petr Mladek
2018-04-27 14:10 ` [PATCH v5 00/11] vsprintf: Prevent silent crashes and consolidate error handling Petr Mladek

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