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time: Add do_timens_ktime_to_host() helper

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

Co-developed-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Andrei Vagin <avagin@gmail.com>
Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20191112012724.250792-13-dima@arista.com
This commit is contained in:
Andrei Vagin
2019-11-12 01:27:01 +00:00
committed by Thomas Gleixner
parent 5a590f35ad
commit 89dd8eecfe
2 changed files with 53 additions and 0 deletions
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36
kernel/time/namespace.c
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@@ -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);