ptp: prevent string overflow

The ida_alloc_max() function can return up to INT_MAX so this buffer is
not large enough.  Also use snprintf() for extra safety.

Fixes: 403376dd ("ptp: add debugfs interface to see applied channel masks")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Link: https://lore.kernel.org/r/d4b1a995-a0cb-4125-aa1d-5fd5044aba1d@moroto.mountainSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/ptp/ptp_clock.c

@@ -220,7 +220,7 @@ struct ptp_clock *ptp_clock_register(struct ptp_clock_info *info,
 	struct ptp_clock *ptp;
 	struct timestamp_event_queue *queue = NULL;
 	int err = 0, index, major = MAJOR(ptp_devt);
-	char debugfsname[8];
+	char debugfsname[16];
 	size_t size;
 
 	if (info->n_alarm > PTP_MAX_ALARMS)
@@ -343,7 +343,7 @@ struct ptp_clock *ptp_clock_register(struct ptp_clock_info *info,
 	}
 
 	/* Debugfs initialization */
-	sprintf(debugfsname, "ptp%d", ptp->index);
+	snprintf(debugfsname, sizeof(debugfsname), "ptp%d", ptp->index);
 	ptp->debugfs_root = debugfs_create_dir(debugfsname, NULL);
 
 	return ptp;