[PATCH] timekeeping: Fix timex status validation for auxiliary clocks

[Miroslav Lichvar]

The timekeeping_validate_timex() function validated the timex status
of an auxiliary system clock even when the status is not to be changed,
which caused unexpected errors for applications that make read-only
clock_adjtime() calls, or set some other timex fields, but without
clearing the status field.

Do the AUX-specific status validation only when the modes field contains
ADJ_STATUS, i.e. the application is actually trying to change the
status. This makes the AUX-specific clock_adjtime() behavior consistent
with CLOCK_REALTIME.

Fixes: 4eca49d0b621 ("timekeeping: Prepare do_adtimex() for auxiliary clocks")
Signed-off-by: Miroslav Lichvar <mlichvar@xxxxxxxxxx>
---
 kernel/time/timekeeping.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 91fa2003351c..c07e562ee4c1 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -2653,7 +2653,8 @@ static int timekeeping_validate_timex(const struct __kernel_timex *txc, bool aux
 
 	if (aux_clock) {
 		/* Auxiliary clocks are similar to TAI and do not have leap seconds */
-		if (txc->status & (STA_INS | STA_DEL))
+		if (txc->modes & ADJ_STATUS &&
+		    txc->status & (STA_INS | STA_DEL))
 			return -EINVAL;
 
 		/* No TAI offset setting */
@@ -2661,7 +2662,8 @@ static int timekeeping_validate_timex(const struct __kernel_timex *txc, bool aux
 			return -EINVAL;
 
 		/* No PPS support either */
-		if (txc->status & (STA_PPSFREQ | STA_PPSTIME))
+		if (txc->modes & ADJ_STATUS &&
+		    txc->status & (STA_PPSFREQ | STA_PPSTIME))
 			return -EINVAL;
 	}
 
-- 
2.53.0