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

[Sergey Senozhatsky]

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