[PATCHv4 06/28] timerfd/timens: Take into account ns clock offsets

[Dmitry Safonov]

From: Andrei Vagin <avagin@xxxxxxxxx>

Make timerfd respect timens offsets.
Provide a helper timens_ktime_to_host() that is useful to wire up
timens to different kernel subsystems.

Signed-off-by: Andrei Vagin <avagin@xxxxxxxxxx>
Co-developed-by: Dmitry Safonov <dima@xxxxxxxxxx>
Signed-off-by: Dmitry Safonov <dima@xxxxxxxxxx>
---
 fs/timerfd.c                   |  3 +++
 include/linux/time_namespace.h | 18 ++++++++++++++++++
 kernel/time_namespace.c        | 27 +++++++++++++++++++++++++++
 3 files changed, 48 insertions(+)

diff --git a/fs/timerfd.c b/fs/timerfd.c
index 6a6fc8aa1de7..9b0c2f65e7e8 100644
--- a/fs/timerfd.c
+++ b/fs/timerfd.c
@@ -26,6 +26,7 @@
 #include <linux/syscalls.h>
 #include <linux/compat.h>
 #include <linux/rcupdate.h>
+#include <linux/time_namespace.h>
 
 struct timerfd_ctx {
 	union {
@@ -196,6 +197,8 @@ static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
 	}
 
 	if (texp != 0) {
+		if (flags & TFD_TIMER_ABSTIME)
+			texp = timens_ktime_to_host(clockid, texp);
 		if (isalarm(ctx)) {
 			if (flags & TFD_TIMER_ABSTIME)
 				alarm_start(&ctx->t.alarm, texp);
diff --git a/include/linux/time_namespace.h b/include/linux/time_namespace.h
index 1dda8af6b9fe..d32b55fad953 100644
--- a/include/linux/time_namespace.h
+++ b/include/linux/time_namespace.h
@@ -56,6 +56,19 @@ 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 timens_offsets *offsets = current->nsproxy->time_ns->offsets;
+
+	if (!offsets) /* fast-path for the root time namespace */
+	       return tim;
+
+	return do_timens_ktime_to_host(clockid, tim, offsets);
+}
+
+
 #else
 static inline struct time_namespace *get_time_ns(struct time_namespace *ns)
 {
@@ -82,6 +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 4828447721ec..b3cffdf2635c 100644
--- a/kernel/time_namespace.c
+++ b/kernel/time_namespace.c
@@ -15,6 +15,33 @@
 #include <linux/sched/task.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 koff;
+
+	switch (clockid) {
+	case CLOCK_MONOTONIC:
+		koff = timespec64_to_ktime(ns_offsets->monotonic);
+		break;
+	case CLOCK_BOOTTIME:
+	case CLOCK_BOOTTIME_ALARM:
+		koff = timespec64_to_ktime(ns_offsets->boottime);
+		break;
+	default:
+		return tim;
+	}
+
+	/* tim - off has to be in [0, KTIME_MAX) */
+	if (tim < koff)
+		tim = 0;
+	else if (KTIME_MAX - tim < -koff)
+		tim = KTIME_MAX;
+	else
+		tim = ktime_sub(tim, koff);
+
+	return tim;
+}
+
 static struct ucounts *inc_time_namespaces(struct user_namespace *ns)
 {
 	return inc_ucount(ns, current_euid(), UCOUNT_TIME_NAMESPACES);
-- 
2.22.0