ipack: ipoctal: fix stack information leak

The tty driver name is used also after registering the driver and must
specifically not be allocated on the stack to avoid leaking information
to user space (or triggering an oops).

Drivers should not try to encode topology information in the tty device
name but this one snuck in through staging without anyone noticing and
another driver has since copied this malpractice.

Fixing the ABI is a separate issue, but this at least plugs the security
hole.

Fixes: ba4dc61f ("Staging: ipack: add support for IP-OCTAL mezzanine board")
Cc: stable@vger.kernel.org      # 3.5
Acked-by: NSamuel Iglesias Gonsalvez <siglesias@igalia.com>
Signed-off-by: NJohan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20210917114622.5412-2-johan@kernel.orgSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/ipack/devices/ipoctal.c

@@ -264,7 +264,6 @@ static int ipoctal_inst_slot(struct ipoctal *ipoctal, unsigned int bus_nr,
 	int res;
 	int i;
 	struct tty_driver *tty;
-	char name[20];
 	struct ipoctal_channel *channel;
 	struct ipack_region *region;
 	void __iomem *addr;
@@ -355,8 +354,11 @@ static int ipoctal_inst_slot(struct ipoctal *ipoctal, unsigned int bus_nr,
 	/* Fill struct tty_driver with ipoctal data */
 	tty->owner = THIS_MODULE;
 	tty->driver_name = KBUILD_MODNAME;
-	sprintf(name, KBUILD_MODNAME ".%d.%d.", bus_nr, slot);
-	tty->name = name;
+	tty->name = kasprintf(GFP_KERNEL, KBUILD_MODNAME ".%d.%d.", bus_nr, slot);
+	if (!tty->name) {
+		res = -ENOMEM;
+		goto err_put_driver;
+	}
 	tty->major = 0;
 
 	tty->minor_start = 0;
@@ -371,8 +373,7 @@ static int ipoctal_inst_slot(struct ipoctal *ipoctal, unsigned int bus_nr,
 	res = tty_register_driver(tty);
 	if (res) {
 		dev_err(&ipoctal->dev->dev, "Can't register tty driver.\n");
-		tty_driver_kref_put(tty);
-		return res;
+		goto err_free_name;
 	}
 
 	/* Save struct tty_driver for use it when uninstalling the device */
@@ -409,6 +410,13 @@ static int ipoctal_inst_slot(struct ipoctal *ipoctal, unsigned int bus_nr,
 				       ipoctal_irq_handler, ipoctal);
 
 	return 0;
+
+err_free_name:
+	kfree(tty->name);
+err_put_driver:
+	tty_driver_kref_put(tty);
+
+	return res;
 }
 
 static inline int ipoctal_copy_write_buffer(struct ipoctal_channel *channel,
@@ -696,6 +704,7 @@ static void __ipoctal_remove(struct ipoctal *ipoctal)
 	}
 
 	tty_unregister_driver(ipoctal->tty_drv);
+	kfree(ipoctal->tty_drv->name);
 	tty_driver_kref_put(ipoctal->tty_drv);
 	kfree(ipoctal);
 }