linux-kernel - [PATCH 2/4] time: make getboottime64 aware of time namespace

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Message-Id: <20201007200015.30868-3-michael.weiss@aisec.fraunhofer.de>
Date:   Wed,  7 Oct 2020 22:00:13 +0200
From:   Michael Weiß <michael.weiss@...ec.fraunhofer.de>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Andrei Vagin <avagin@...il.com>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Christian Brauner <christian.brauner@...ntu.com>
Cc:     linux-kernel@...r.kernel.org,
        Michael Weiß <michael.weiss@...ec.fraunhofer.de>
Subject: [PATCH 2/4] time: make getboottime64 aware of time namespace

getboottime64() provides the time stamp of system boot. In case of
time namespaces, the offset to the boot time stamp was not applied
earlier. However, getboottime64 is used e.g., in /proc/stat to print
the system boot time to userspace. In container runtimes which utilize
time namespaces to virtualize boottime of a container, this leaks
information about the host system boot time.

Therefore, we make getboottime64() to respect the time namespace offset
for boottime by subtracting the boottime offset.

Signed-off-by: Michael Weiß <michael.weiss@...ec.fraunhofer.de>
---
 kernel/time/timekeeping.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 4c47f388a83f..67530cdb389e 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -17,6 +17,7 @@
 #include <linux/clocksource.h>
 #include <linux/jiffies.h>
 #include <linux/time.h>
+#include <linux/time_namespace.h>
 #include <linux/tick.h>
 #include <linux/stop_machine.h>
 #include <linux/pvclock_gtod.h>
@@ -2154,6 +2155,8 @@ void getboottime64(struct timespec64 *ts)
 {
 	struct timekeeper *tk = &tk_core.timekeeper;
 	ktime_t t = ktime_sub(tk->offs_real, tk->offs_boot);
+	/* shift boot time stamp according to the timens offset */
+	t = timens_ktime_to_host(CLOCK_BOOTTIME, t);
 
 	*ts = ktime_to_timespec64(t);
 }
-- 
2.20.1