Re: [PATCH v5 10/11] vsprintf: WARN() on invalid pointer access

From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Petr Mladek <pmladek@suse.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	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 10/11] vsprintf: WARN() on invalid pointer access
Date: Thu, 26 Apr 2018 10:28:05 +0900	[thread overview]
Message-ID: <20180426012805.GA3282@jagdpanzerIV> (raw)
In-Reply-To: <20180425111251.13246-11-pmladek@suse.com>

On (04/25/18 13:12), Petr Mladek wrote:
[..]
>   /*
>    * This is not a fool-proof test. 99% of the time that this will fault is
>    * due to a bad pointer, not one that crosses into bad memory. Just test
> @@ -623,8 +626,12 @@ static const char *check_pointer_access(const void *ptr)
>  	if (!ptr)
>  		return "(null)";
>  
> -	if (probe_kernel_address(ptr, byte))
> +	/* Prevent silent crashes when called in printk_safe context. */
> +	if (probe_kernel_address(ptr, byte)) {
> +		WARN(!panic_on_warn && !test_printf_pointer_access,
> +		     "vsprintf: invalid pointer address\n");
>  		return "(efault)";
> +	}

Can we have a rate-limited print out here? Or may be even a WARN_ONCE()?
Yes, printk()-s from check_pointer_access() are OK, printk_safe() helps us,
but at the same time every single invalid pointer access printk()-message
will log_store() WARN() extra entries. Theoretically, this can harm. What
do you think?

	-ss