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

Dmitry Safonov
2019-11-12T01:27:01Z

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