[PATCH] rtc: hctosys: Add missing range error reporting

[Maciej W. Rozycki]

Fix an issue with the 32-bit range error path in `rtc_hctosys' where no 
error code is set and consequently the successful preceding call result 
from `rtc_read_time' is propagated to `rtc_hctosys_ret'.  This in turn 
makes any subsequent call to `hctosys_show' incorrectly report in sysfs 
that the system time has been set from this RTC while it has not.

Set the error to ERANGE then if we can't express the result due to an 
overflow.

Signed-off-by: Maciej W. Rozycki <macro@xxxxxxxxxxxxxx>
Fixes: b3a5ac42ab18 ("rtc: hctosys: Ensure system time doesn't overflow time_t")
Cc: stable@xxxxxxxxxxxxxxx # 4.17+
---
 drivers/rtc/hctosys.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

linux-rtc-hctosys-range.diff
Index: linux-20181008-swarm64-eb/drivers/rtc/hctosys.c
===================================================================
--- linux-20181008-swarm64-eb.orig/drivers/rtc/hctosys.c
+++ linux-20181008-swarm64-eb/drivers/rtc/hctosys.c
@@ -50,8 +50,10 @@ static int __init rtc_hctosys(void)
 	tv64.tv_sec = rtc_tm_to_time64(&tm);
 
 #if BITS_PER_LONG == 32
-	if (tv64.tv_sec > INT_MAX)
+	if (tv64.tv_sec > INT_MAX) {
+		err = -ERANGE;
 		goto err_read;
+	}
 #endif
 
 	err = do_settimeofday64(&tv64);