Commit fb8741a0 authored Aug 01, 2016 by John Stultz Committed by Dmitry Shmidt Aug 11, 2016

FROMLIST: proc: Fix timerslack_ns CAP_SYS_NICE check when adjusting self

In changing from checking ptrace_may_access(p, PTRACE_MODE_ATTACH_FSCREDS)
to capable(CAP_SYS_NICE), I missed that ptrace_my_access succeeds
when p == current, but the CAP_SYS_NICE doesn't.

Thus while the previous commit was intended to loosen the needed
privledges to modify a processes timerslack, it needlessly restricted
a task modifying its own timerslack via the proc/<tid>/timerslack_ns
(which is permitted also via the PR_SET_TIMERSLACK method).

This patch corrects this by checking if p == current before checking
the CAP_SYS_NICE value.

Cc: Kees Cook <keescook@chromium.org>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
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>
Mailing-list-url: http://www.spinics.net/lists/kernel/msg2317488.html


Change-Id: Ia3e8aff07c2d41f55b6617502d33c39b7d781aac
Signed-off-by: John Stultz <john.stultz@linaro.org>

parent edb97738

fs/proc/base.c

+19 −15

Original line number	Diff line number	Diff line
		@@ -2260,6 +2260,7 @@ static ssize_t timerslack_ns_write(struct file file, const char __user buf,
		if (!p)
		return -ESRCH;

		if (p != current) {
		if (!capable(CAP_SYS_NICE)) {
		count = -EPERM;
		goto out;
		@@ -2270,6 +2271,7 @@ static ssize_t timerslack_ns_write(struct file file, const char __user buf,
		count = err;
		goto out;
		}
		}

		task_lock(p);
		if (slack_ns == 0)
		@@ -2294,14 +2296,16 @@ static int timerslack_ns_show(struct seq_file m, void v)
		if (!p)
		return -ESRCH;

		if (p != current) {

		if (!capable(CAP_SYS_NICE)) {
		err = -EPERM;
		goto out;
		}

		err = security_task_getscheduler(p);
		if (err)
		goto out;
		}

		task_lock(p);
		seq_printf(m, "%llu\n", p->timer_slack_ns);