ptp: Ensure info->enable callback is always set

JIRA: https://issues.redhat.com/browse/RHEL-85028
Upstream Status: net.git commit fd53aa4
CVE: CVE-2025-21814

commit fd53aa4
Author: Thomas Weißschuh <linux@weissschuh.net>
Date:   Thu Jan 23 08:22:40 2025 +0100

    ptp: Ensure info->enable callback is always set

    The ioctl and sysfs handlers unconditionally call the ->enable callback.
    Not all drivers implement that callback, leading to NULL dereferences.
    Example of affected drivers: ptp_s390.c, ptp_vclock.c and ptp_mock.c.

    Instead use a dummy callback if no better was specified by the driver.

    Fixes: d94ba80 ("ptp: Added a brand new class driver for ptp clocks.")
    Cc: stable@vger.kernel.org
    Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
    Acked-by: Richard Cochran <richardcochran@gmail.com>
    Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
    Link: https://patch.msgid.link/20250123-ptp-enable-v1-1-b015834d3a47@weissschuh.net
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: Hangbin Liu <haliu@redhat.com>

Author: Hangbin Liu

drivers/ptp/ptp_clock.c

@@ -192,6 +192,11 @@ static int ptp_getcycles64(struct ptp_clock_info *info, struct timespec64 *ts)
 		return info->gettime64(info, ts);
 }
 
+static int ptp_enable(struct ptp_clock_info *ptp, struct ptp_clock_request *request, int on)
+{
+	return -EOPNOTSUPP;
+}
+
 static void ptp_aux_kworker(struct kthread_work *work)
 {
 	struct ptp_clock *ptp = container_of(work, struct ptp_clock,
@@ -254,6 +259,9 @@ struct ptp_clock *ptp_clock_register(struct ptp_clock_info *info,
 			ptp->info->getcrosscycles = ptp->info->getcrosststamp;
 	}
 
+	if (!ptp->info->enable)
+		ptp->info->enable = ptp_enable;
+
 	if (ptp->info->do_aux_work) {
 		kthread_init_delayed_work(&ptp->aux_work, ptp_aux_kworker);
 		ptp->kworker = kthread_create_worker(0, "ptp%d", ptp->index);