Re: [PATCH 1/2] Fix printk() on ERR_PTR()

[Andrew Morton <akpm@linux-foundation.org>]

On Sun, 10 May 2015 21:42:15 +0200 Richard Weinberger <richard@nod.at> wrote:

> vbin_printf() checks whether the provided pointer is larger
> than -PAGE_SIZE such that it does not explode on ERR_PTR() pointers.
> printk() does not.
> 
> Let's add this check also to the printk() code such that
> trace_printk() and printk() are consistent again.
> 
> ..
>
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -511,7 +511,8 @@ char *string(char *buf, char *end, const char *s, struct printf_spec spec)
>  {
>  	int len, i;
>  
> -	if ((unsigned long)s < PAGE_SIZE)
> +	if ((unsigned long)s > (unsigned long)-PAGE_SIZE ||

hm, PAGE_SIZE has type ulong, so is the cast needed?

> +	    (unsigned long)s < PAGE_SIZE)

This would be a place for

	if (!within(PAGE_SIZE, (unsigned long)s, -PAGE_SIZE))
  		s = "(null)";

I'm counting at least five implementations of within(), not all the same.

Maybe.  Both the lower and upper bounds will sometimes want inclusive
semantics, sometimes exclusive.