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: 98f76206b335 ("compat: Cleanup in_compat_syscall() callers")
Reported-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20191121000303.126523-1-dima@arista.com

diff --git a/kernel/time/time.c b/kernel/time/time.c
index 5c54ca632d08c0a5bf862b1c499faeb17bec1dc6..83f403e7a15c48747846be36fa76e0983d7ab429 100644 (file)
--- a/kernel/time/time.c
+++ b/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;