[PATCH] fs/timerfd: reject ALARM timerfds without CAP_WAKE_ALARM

From: Eric Caruso <ejcaruso@chromium.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Todd Poynor <toddpoynor@google.com>,
	linux-kernel@vger.kernel.org, Eric Caruso <ejcaruso@google.com>
Subject: [PATCH] fs/timerfd: reject ALARM timerfds without CAP_WAKE_ALARM
Date: Wed,  8 Jun 2016 16:08:59 -0700	[thread overview]
Message-ID: <1465427339-96209-1-git-send-email-ejcaruso@chromium.org> (raw)

From: Eric Caruso <ejcaruso@google.com>

timerfd gives processes a way to set wake alarms, but
unlike timers made using timer_create, timerfds don't
check whether the process has CAP_WAKE_ALARM before
setting alarm-time timers. CAP_WAKE_ALARM is supposed to
gate this behavior and so it makes sense that we should
deny permission to create such timerfds if the process
doesn't have this capability.

Signed-off-by: Eric Caruso <ejcaruso@google.com>
---
 fs/timerfd.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/fs/timerfd.c b/fs/timerfd.c
index 053818d..9ae4abb 100644
--- a/fs/timerfd.c
+++ b/fs/timerfd.c
@@ -390,6 +390,11 @@ SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
 	     clockid != CLOCK_BOOTTIME_ALARM))
 		return -EINVAL;
 
+	if (!capable(CAP_WAKE_ALARM) &&
+	    (clockid == CLOCK_REALTIME_ALARM ||
+	     clockid == CLOCK_BOOTTIME_ALARM))
+		return -EPERM;
+
 	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
 	if (!ctx)
 		return -ENOMEM;
@@ -433,6 +438,11 @@ static int do_timerfd_settime(int ufd, int flags,
 		return ret;
 	ctx = f.file->private_data;
 
+	if (!capable(CAP_WAKE_ALARM) && isalarm(ctx)) {
+		fdput(f);
+		return -EPERM;
+	}
+
 	timerfd_setup_cancel(ctx, flags);
 
 	/*
-- 
2.8.0.rc3.226.g39d4020
