[PATCH] time: Zerofy padding in __kernel_timespec on 32-bit

From: Dmitry Safonov
Date: Wed Nov 20 2019 - 19:03:27 EST

On compat interfaces, the high order bits of nanoseconds should
be zeroed out. This is because the application code or the libc
do not guarantee zeroing of these. If used without zeroing,
kernel might be at risk of using timespec values incorrectly.

Originally it was handled correctly, but lost during is_compat_syscall()
cleanup. Revert the condition back to check CONFIG_64BIT.

Reported-by: Ben Hutchings <ben.hutchings@xxxxxxxxxxxxxxx>
Fixes: 98f76206b335 ("compat: Cleanup in_compat_syscall() callers")
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Ben Hutchings <ben.hutchings@xxxxxxxxxxxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Cc: Stephen Boyd <sboyd@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: y2038@xxxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx # v4.20+
Signed-off-by: Dmitry Safonov <dima@xxxxxxxxxx>
kernel/time/time.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/time/time.c b/kernel/time/time.c
index 5c54ca632d08..1cb045c5c97e 100644
--- a/kernel/time/time.c
+++ b/kernel/time/time.c
@@ -881,7 +881,7 @@ int get_timespec64(struct timespec64 *ts,
ts->tv_sec = kts.tv_sec;

/* Zero out the padding for 32 bit systems or in compat mode */
- if (IS_ENABLED(CONFIG_64BIT_TIME) && in_compat_syscall())
+ if (IS_ENABLED(CONFIG_64BIT_TIME) && (!IS_ENABLED(CONFIG_64BIT) || in_compat_syscall()))
kts.tv_nsec &= 0xFFFFFFFFUL;

ts->tv_nsec = kts.tv_nsec;