Patch "tap: reference to KVA of an unloaded module causes kernel panic" has been added to the 4.13-stable tree

This is a note to let you know that I've just added the patch titled

tap: reference to KVA of an unloaded module causes kernel panic

to the 4.13-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
tap-reference-to-kva-of-an-unloaded-module-causes-kernel-panic.patch
and it can be found in the queue-4.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Girish Moodalbail <[email protected]>
Date: Fri, 27 Oct 2017 00:00:16 -0700
Subject: tap: reference to KVA of an unloaded module causes kernel panic

From: Girish Moodalbail <[email protected]>

[ Upstream commit dea6e19f4ef746aa18b4c33d1a7fed54356796ed ]

The commit 9a393b5d5988 ("tap: tap as an independent module") created a separate tap module that implements tap functionality and exports interfaces that will be used by macvtap and ipvtap modules to create create respective tap devices.

However, that patch introduced a regression wherein the modules macvtap and ipvtap can be removed (through modprobe -r) while there are applications using the respective /dev/tapX devices. These applications cause kernel to hold reference to /dev/tapX through 'struct cdev macvtap_cdev' and 'struct cdev ipvtap_dev' defined in macvtap and ipvtap modules respectively. So, when the application is later closed the kernel panics because we are referencing KVA that is present in the unloaded modules.

----------8<------- Example ----------8<----------

$ sudo ip li add name mv0 link enp7s0 type macvtap
$ sudo ip li show mv0 |grep mv0| awk -e '{print $1 $2}'
  14:mv0@enp7s0:
$ cat /dev/tap14 &
$ lsmod |egrep -i 'tap|vlan'
macvtap                16384  0
macvlan                24576  1 macvtap
tap                    24576  3 macvtap
$ sudo modprobe -r macvtap
$ fg
cat /dev/tap14
^C

<...system panics...>

BUG: unable to handle kernel paging request at ffffffffa038c500
IP: cdev_put+0xf/0x30

----------8<-----------------8<----------

The fix is to set cdev.owner to the module that creates the tap device (either macvtap or ipvtap). With this set, the operations (in fs/char_dev.c) on char device holds and releases the module through cdev_get() and cdev_put() and will not allow the module to unload prematurely.

---
 drivers/net/ipvlan/ipvtap.c |    4 ++--
 drivers/net/macvtap.c       |    4 ++--
 drivers/net/tap.c           |    5 +++--
 include/linux/if_tap.h      |    4 ++--
 4 files changed, 9 insertions(+), 8 deletions(-)

@@ -197,8 +197,8 @@ static int ipvtap_init(void)
 {
 	int err;
 
-	err = tap_create_cdev(&ipvtap_cdev, &ipvtap_major, "ipvtap");
-
+	err = tap_create_cdev(&ipvtap_cdev, &ipvtap_major, "ipvtap",
+			      THIS_MODULE);
 	if (err)
 		goto out1;
 

@@ -204,8 +204,8 @@ static int macvtap_init(void)
 {
 	int err;
 
-	err = tap_create_cdev(&macvtap_cdev, &macvtap_major, "macvtap");
-
+	err = tap_create_cdev(&macvtap_cdev, &macvtap_major, "macvtap",
+			      THIS_MODULE);
 	if (err)
 		goto out1;
 

@@ -1252,8 +1252,8 @@ static int tap_list_add(dev_t major, con
 	return 0;
 }
 
-int tap_create_cdev(struct cdev *tap_cdev,
-		    dev_t *tap_major, const char *device_name)
+int tap_create_cdev(struct cdev *tap_cdev, dev_t *tap_major,
+		    const char *device_name, struct module *module)
 {
 	int err;
 

@@ -1262,6 +1262,7 @@ int tap_create_cdev(struct cdev *tap_cde
 		goto out1;
 
 	cdev_init(tap_cdev, &tap_fops);
+	tap_cdev->owner = module;
 	err = cdev_add(tap_cdev, *tap_major, TAP_NUM_DEVS);
 	if (err)
 		goto out2;

@@ -73,8 +73,8 @@ void tap_del_queues(struct tap_dev *tap)
 int tap_get_minor(dev_t major, struct tap_dev *tap);
 void tap_free_minor(dev_t major, struct tap_dev *tap);
 int tap_queue_resize(struct tap_dev *tap);
-int tap_create_cdev(struct cdev *tap_cdev,
-		    dev_t *tap_major, const char *device_name);
+int tap_create_cdev(struct cdev *tap_cdev, dev_t *tap_major,
+		    const char *device_name, struct module *module);
 void tap_destroy_cdev(dev_t major, struct cdev *tap_cdev);
 
 #endif /*_LINUX_IF_TAP_H_*/

Patches currently in stable-queue which might be from [email protected] are

queue-4.13/tap-reference-to-kva-of-an-unloaded-module-causes-kernel-panic.patch queue-4.13/tap-double-free-in-error-path-in-tap_open.patch