[PATCHv8 12/34] kernel: Add do_timens_ktime_to_host() helper

From: Dmitry Safonov <dima@arista.com>
To: linux-kernel@vger.kernel.org
Cc: Dmitry Safonov <0x7f454c46@gmail.com>,
	Andrei Vagin <avagin@gmail.com>, Dmitry Safonov <dima@arista.com>,
	Adrian Reber <adrian@lisas.de>, Andrei Vagin <avagin@openvz.org>,
	Andy Lutomirski <luto@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	Christian Brauner <christian.brauner@ubuntu.com>,
	Cyrill Gorcunov <gorcunov@openvz.org>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
	Jann Horn <jannh@google.com>, Jeff Dike <jdike@addtoit.com>,
	Oleg Nesterov <oleg@redhat.com>,
	Pavel Emelyanov <xemul@virtuozzo.com>,
	Shuah Khan <shuah@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	containers@lists.linux-foundation.org, criu@openvz.org,
	linux-api@vger.kernel.org, x86@kernel.org
Subject: [PATCHv8 12/34] kernel: Add do_timens_ktime_to_host() helper
Date: Tue, 12 Nov 2019 01:27:01 +0000	[thread overview]
Message-ID: <20191112012724.250792-13-dima@arista.com> (raw)
In-Reply-To: <20191112012724.250792-1-dima@arista.com>

From: Andrei Vagin <avagin@gmail.com>

The helper subtracts namespace's clock offset from the given time
and checks that the result is in [0, KTIME_MAX].

Signed-off-by: Andrei Vagin <avagin@gmail.com>
Co-developed-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Dmitry Safonov <dima@arista.com>
---
 include/linux/time_namespace.h | 17 ++++++++++++++++
 kernel/time/namespace.c        | 36 ++++++++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+)

diff --git a/include/linux/time_namespace.h b/include/linux/time_namespace.h
index 3d429c7ecca5..a68b1ab7b5bb 100644
--- a/include/linux/time_namespace.h
+++ b/include/linux/time_namespace.h
@@ -57,6 +57,18 @@ static inline void timens_add_boottime(struct timespec64 *ts)
 	*ts = timespec64_add(*ts, ns_offsets->boottime);
 }
 
+ktime_t do_timens_ktime_to_host(clockid_t clockid, ktime_t tim,
+				struct timens_offsets *offsets);
+static inline ktime_t timens_ktime_to_host(clockid_t clockid, ktime_t tim)
+{
+	struct time_namespace *ns = current->nsproxy->time_ns;
+
+	if (likely(ns == &init_time_ns))
+		return tim;
+
+	return do_timens_ktime_to_host(clockid, tim, &ns->offsets);
+}
+
 #else
 static inline struct time_namespace *get_time_ns(struct time_namespace *ns)
 {
@@ -83,6 +95,11 @@ static inline int timens_on_fork(struct nsproxy *nsproxy, struct task_struct *ts
 
 static inline void timens_add_monotonic(struct timespec64 *ts) {}
 static inline void timens_add_boottime(struct timespec64 *ts) {}
+
+static inline ktime_t timens_ktime_to_host(clockid_t clockid, ktime_t tim)
+{
+	return tim;
+}
 #endif
 
 #endif /* _LINUX_TIMENS_H */
diff --git a/kernel/time/namespace.c b/kernel/time/namespace.c
index c2a58e45fc4b..1a0fbaa5d2d4 100644
--- a/kernel/time/namespace.c
+++ b/kernel/time/namespace.c
@@ -16,6 +16,42 @@
 #include <linux/err.h>
 #include <linux/mm.h>
 
+ktime_t do_timens_ktime_to_host(clockid_t clockid, ktime_t tim,
+				struct timens_offsets *ns_offsets)
+{
+	ktime_t offset;
+
+	switch (clockid) {
+	case CLOCK_MONOTONIC:
+		offset = timespec64_to_ktime(ns_offsets->monotonic);
+		break;
+	case CLOCK_BOOTTIME:
+	case CLOCK_BOOTTIME_ALARM:
+		offset = timespec64_to_ktime(ns_offsets->boottime);
+		break;
+	default:
+		return tim;
+	}
+
+	/*
+	 * Check that @tim value is in [offset, KTIME_MAX + offset]
+	 * and subtract offset.
+	 */
+	if (tim < offset) {
+		/*
+		 * User can specify @tim *absolute* value - if it's lesser than
+		 * the time namespace's offset - it's already expired.
+		 */
+		tim = 0;
+	} else {
+		tim = ktime_sub(tim, offset);
+		if (unlikely(tim > KTIME_MAX))
+			tim = KTIME_MAX;
+	}
+
+	return tim;
+}
+
 static struct ucounts *inc_time_namespaces(struct user_namespace *ns)
 {
 	return inc_ucount(ns, current_euid(), UCOUNT_TIME_NAMESPACES);
-- 
2.24.0

