linux-kernel - Re: [PATCH] vsprintf: kptr_restrict is okay in IRQ when 2

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Message-ID: <CAGXu5jK02bj4XxRE60zXQFToDcHGRKY57E0k6-W23+Br9vyKjA@mail.gmail.com>
Date:	Fri, 5 Feb 2016 12:46:46 -0800
From:	Kees Cook <keescook@...omium.org>
To:	"Jason A. Donenfeld" <Jason@...c4.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] vsprintf: kptr_restrict is okay in IRQ when 2

On Fri, Feb 5, 2016 at 5:45 AM, Jason A. Donenfeld <Jason@...c4.com> wrote:
> The kptr_restrict flag, when set to 1, only prints the kernel
> address when the user has CAP_SYSLOG. When it is set to 2, the
> kernel address is always printed as zero. When set to 1, this
> needs to check whether or not we're in IRQ. However, when set to
> 2, this check is unneccessary, and produces confusing results
> in dmesg. Thus, only make sure we're not in IRQ when mode 1 is
> used, but not mode 2.

Cool, nice fix.

>
> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> ---
>  lib/vsprintf.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 80d8ce5..fab875f 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -1609,8 +1609,8 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
>                  * %pK cannot be used in IRQ context because its test
>                  * for CAP_SYSLOG would be meaningless.
>                  */
> -               if (kptr_restrict && (in_irq() || in_serving_softirq() ||
> -                                     in_nmi())) {
> +               if (kptr_restrict == 1 && (in_irq() || in_serving_softirq() ||
> +                                          in_nmi())) {

Instead of doing a double-check of kptr_restrict, how about moving
this logic down into the "case 1" test? I think that would be more
readable in the end.

-Kees

>                         if (spec.field_width == -1)
>                                 spec.field_width = default_width;
>                         return string(buf, end, "pK-error", spec);
> --
> 2.7.0
>



-- 
Kees Cook
Chrome OS & Brillo Security