sys/sysinfo: Respect boottime inside time namespace

The sysinfo() syscall includes uptime in seconds but has no correction for
time namespaces which makes it inconsistent with the /proc/uptime inside of
a time namespace.

Add the missing time namespace adjustment call.
Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Dmitry Safonov <dima@arista.com>
Link: https://lkml.kernel.org/r/20200303150638.7329-1-chrubis@suse.cz

kernel/sys.c

@@ -47,6 +47,7 @@
 #include <linux/syscalls.h>
 #include <linux/kprobes.h>
 #include <linux/user_namespace.h>
+#include <linux/time_namespace.h>
 #include <linux/binfmts.h>
 
 #include <linux/sched.h>
@@ -2546,6 +2547,7 @@ static int do_sysinfo(struct sysinfo *info)
 	memset(info, 0, sizeof(struct sysinfo));
 
 	ktime_get_boottime_ts64(&tp);
+	timens_add_boottime(&tp);
 	info->uptime = tp.tv_sec + (tp.tv_nsec ? 1 : 0);
 
 	get_avenrun(info->loads, 0, SI_LOAD_SHIFT - FSHIFT);