[v2] time: Validate the usec before covert to nsec in do_adjtimex

[ZhangXiaoxu]

When covert the usec to nsec, it will multiple 1000, it maybe
overflow and lead an undefined behavior.

For example, users may input an negative tv_usec values when
call adjtimex syscall, then multiple 1000 maybe overflow it
to a positive and legal number.

So, we should validate the usec before coverted it to nsec.

Signed-off-by: ZhangXiaoxu <zhangxiaoxu5@xxxxxxxxxx>
---
 kernel/time/timekeeping.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 44b726b..778796d 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -2321,6 +2321,9 @@ int do_adjtimex(struct __kernel_timex *txc)
 
 	if (txc->modes & ADJ_SETOFFSET) {
 		struct timespec64 delta;
+
+		if (txc->time.tv_usec < 0 || txc->time.tv_usec >= USEC_PER_SEC)
+			return -EINVAL;
 		delta.tv_sec  = txc->time.tv_sec;
 		delta.tv_nsec = txc->time.tv_usec;
 		if (!(txc->modes & ADJ_NANO))
-- 
2.7.4