From fb8741a0ba7445503ebe648fd96cccc34d7d2088 Mon Sep 17 00:00:00 2001
From: John Stultz <john.stultz@linaro.org>
Date: Mon, 1 Aug 2016 16:49:07 -0700
Subject: 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>
---
 fs/proc/base.c | 34 +++++++++++++++++++---------------
 1 file changed, 19 insertions(+), 15 deletions(-)

(limited to 'fs/proc')

diff --git a/fs/proc/base.c b/fs/proc/base.c
index ac5d2aea63b5..49348349e156 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2260,15 +2260,17 @@ static ssize_t timerslack_ns_write(struct file *file, const char __user *buf,
 	if (!p)
 		return -ESRCH;
 
-	if (!capable(CAP_SYS_NICE)) {
-		count = -EPERM;
-		goto out;
-	}
+	if (p != current) {
+		if (!capable(CAP_SYS_NICE)) {
+			count = -EPERM;
+			goto out;
+		}
 
-	err = security_task_setscheduler(p);
-	if (err) {
-		count = err;
-		goto out;
+		err = security_task_setscheduler(p);
+		if (err) {
+			count = err;
+			goto out;
+		}
 	}
 
 	task_lock(p);
@@ -2294,14 +2296,16 @@ static int timerslack_ns_show(struct seq_file *m, void *v)
 	if (!p)
 		return -ESRCH;
 
-	if (!capable(CAP_SYS_NICE)) {
-		err = -EPERM;
-		goto out;
-	}
+	if (p != current) {
 
-	err = security_task_getscheduler(p);
-	if (err)
-		goto out;
+		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);
-- 
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