Re: [PATCH v5 03/11] vsprintf: Consistent %pK handling for kptr_restrict == 0

[Andy Shevchenko]

On Wed, 2018-04-25 at 13:12 +0200, Petr Mladek wrote:
> restricted_pointer() pretends that it prints the address when
> kptr_restrict
> is set to zero. But it is never called in this situation. Instead,
> pointer() falls back to ptr_to_id() and hashes the pointer.
> 
> This patch removes the potential confusion. klp_restrict is checked
> only
> in restricted_pointer().
> 
> It actually fixes a small race when the address might get printed
> unhashed:
> 
> CPU0                            CPU1
> 
> pointer()
>   if (!kptr_restrict)
>      /* for example set to 2 */
>   restricted_pointer()
> 				/* echo 0
> >/proc/sys/kernel/kptr_restrict */
> 				proc_dointvec_minmax_sysadmin()
> 				  klpr_restrict = 0;
>     switch(kptr_restrict)
>       case 0:
> 	break:
> 
>     number()
> 

FWIW, 
Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>

> Fixes: commit ef0010a30935de4e0211 ("vsprintf: don't use
> 'restricted_pointer()' when not restricting")
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Cc: Tobin Harding <me@xxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Signed-off-by: Petr Mladek <pmladek@xxxxxxxx>
> ---
>  lib/vsprintf.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index eef9f725e9ff..2678dfe61d73 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -694,8 +694,8 @@ char *restricted_pointer(char *buf, char *end,
> const void *ptr,
>  {
>  	switch (kptr_restrict) {
>  	case 0:
> -		/* Always print %pK values */
> -		break;
> +		/* Handle as %p, hash and do _not_ leak addresses. */
> +		return ptr_to_id(buf, end, ptr, spec);
>  	case 1: {
>  		const struct cred *cred;
>  
> @@ -1915,8 +1915,6 @@ char *pointer(const char *fmt, char *buf, char
> *end, void *ptr,
>  			return buf;
>  		}
>  	case 'K':
> -		if (!kptr_restrict)
> -			break;
>  		return restricted_pointer(buf, end, ptr, spec);
>  	case 'N':
>  		return netdev_bits(buf, end, ptr, fmt);

-- 
Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Intel Finland Oy