timekeeping: Fix timex status validation for auxiliary clocks

The timekeeping_validate_timex() function validates the timex status
of an auxiliary system clock even when the status is not to be changed,
which causes 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 <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Link: https://patch.msgid.link/[e-mail]

kernel/time/timekeeping.c

···
 
 	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 */
···
 			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;
 	}