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From: ebiederm@xmission.com (Eric W. Biederman)
To: bmgordon@google.com
Cc: linux-kernel@vger.kernel.org,
	John Stultz <john.stultz@linaro.org>,
	Kees Cook <keescook@chromium.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Arjan van de Ven <arjan@linux.intel.com>,
	Oren Laadan <orenl@cellrox.com>,
	Ruchi Kandoi <kandoiruchi@google.com>,
	Rom Lemarchand <romlem@android.com>, Todd Kjos <tkjos@google.com>,
	Colin Cross <ccross@android.com>, Nick Kralevich <nnk@google.com>,
	Dmitry Shmidt <dimitrysh@google.com>,
	Elliott Hughes <enh@google.com>,
	Android Kernel Team <kernel-team@android.com>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] proc: use ns_capable instead of capable for timerslack_ns
Date: Thu, 25 Oct 2018 13:56:27 -0500	[thread overview]
Message-ID: <87in1pn9d0.fsf@xmission.com> (raw)
In-Reply-To: <20181017224738.193598-1-bmgordon@google.com> (bmgordon@google.com's message of "Wed, 17 Oct 2018 16:47:38 -0600")

bmgordon@google.com writes:

> 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.

The goal seems legitimate.  However the permission checks look wrong.

In particular the choice of user namespace should be
"p->cred->user_ns".  This will limit this to tasks that have
CAP_SYS_NICE in the same namespace as the task that is being modified.

Testing file->f_cred->user_ns it is testing whoever opened the file and
that could be anyone.

Eric


> 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;
>  		}

  parent reply	other threads:[~2018-10-25 18:57 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-17 22:47 bmgordon
2018-10-25 17:09 ` Benjamin Gordon
2018-10-25 17:20 ` John Stultz
2018-10-25 18:56 ` Eric W. Biederman [this message]
2018-10-30 16:40   ` Benjamin Gordon

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