time: Zero the upper 32-bits in __kernel_timespec on 32-bit

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.

Fixes: 98f7620 ("compat: Cleanup in_compat_syscall() callers")
Reported-by: Ben Hutchings <[email protected]>
Signed-off-by: Dmitry Safonov <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Cc: [email protected]
Link: https://lore.kernel.org/r/[email protected]

Author: 0x7f454c46

kernel/time/time.c

@@ -881,7 +881,8 @@ 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;