[PATCH 5.3 006/105] time: Zero the upper 32-bits in __kernel_timespec on 32-bit

From: Greg Kroah-Hartman
Date: Wed Dec 11 2019 - 10:13:47 EST

From: Dmitry Safonov <dima@xxxxxxxxxx>

commit 7b8474466ed97be458c825f34a85f2c2b84c3f95 upstream.

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@xxxxxxxxxxxxxxx>
Signed-off-by: Dmitry Safonov <dima@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/20191121000303.126523-1-dima@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

kernel/time/time.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- 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())
+ in_compat_syscall()))
kts.tv_nsec &= 0xFFFFFFFFUL;

ts->tv_nsec = kts.tv_nsec;