Re: [RFC][PATCH] printf: Harden accessing pointer dereference in vsprintf()

[Sergey Senozhatsky]

On (25/01/06 17:27), Steven Rostedt wrote:
> @@ -695,12 +695,18 @@ static char *error_string(char *buf, char *end, const char *s,
>   */
>  static const char *check_pointer_msg(const void *ptr)
>  {
> +	char ch;
> +
>  	if (!ptr)
>  		return "(null)";
>  
>  	if ((unsigned long)ptr < PAGE_SIZE || IS_ERR_VALUE(ptr))
>  		return "(efault)";
>  
> +	/* Just test a single byte */
> +	if (copy_from_kernel_nofault(&ch, ptr, 1) < 0)
> +		return "(efault)";
> +

I might be wrong, but I recall that copy_from_kernel() (previously known
as probe_kernel_read()) did cause boot regressions in the past.  E.g.
Petr's commit 2ac5a3bf7042 ("vsprintf: Do not break early boot with
probing addresses").