Re: [PATCH] proc: use ns_capable instead of capable for timerslack_ns

[John Stultz <john.stultz@linaro.org>]

On Wed, Oct 17, 2018 at 3:47 PM,  <bmgordon@google.com> wrote:
> From: Benjamin Gordon <bmgordon@google.com>
>
> Access to timerslack_ns is controlled by a process having CAP_SYS_NICE
> in its effective capability set, but the current check looks in the root
> namespace instead of the process' user namespace.  Since a process is
> allowed to do other activities controlled by CAP_SYS_NICE inside a
> namespace, it should also be able to adjust timerslack_ns.
>
> Signed-off-by: Benjamin Gordon <bmgordon@google.com>
> Cc: John Stultz <john.stultz@linaro.org>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: "Serge E. Hallyn" <serge@hallyn.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Arjan van de Ven <arjan@linux.intel.com>
> Cc: Oren Laadan <orenl@cellrox.com>
> Cc: Ruchi Kandoi <kandoiruchi@google.com>
> Cc: Rom Lemarchand <romlem@android.com>
> Cc: Todd Kjos <tkjos@google.com>
> Cc: Colin Cross <ccross@android.com>
> Cc: Nick Kralevich <nnk@google.com>
> Cc: Dmitry Shmidt <dimitrysh@google.com>
> Cc: Elliott Hughes <enh@google.com>
> Cc: Android Kernel Team <kernel-team@android.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> ---
>  fs/proc/base.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 7e9f07bf260d..4b50937dff80 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -2356,7 +2356,7 @@ static ssize_t timerslack_ns_write(struct file *file, const char __user *buf,
>                 return -ESRCH;
>
>         if (p != current) {
> -               if (!capable(CAP_SYS_NICE)) {
> +               if (!ns_capable(file->f_cred->user_ns, CAP_SYS_NICE)) {
>                         count = -EPERM;
>                         goto out;
>                 }
> @@ -2393,7 +2393,7 @@ static int timerslack_ns_show(struct seq_file *m, void *v)
>
>         if (p != current) {
>
> -               if (!capable(CAP_SYS_NICE)) {
> +               if (!ns_capable(seq_user_ns(m), CAP_SYS_NICE)) {
>                         err = -EPERM;
>                         goto out;
>                 }

Looks reasonable to me.
Acked-by: John Stultz <john.stultz@linaro.org>

thanks
-john