4.13-stable review patch. If anyone has any objections, please let me know.
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From: Girish Moodalbail girish.moodalbail@oracle.com
[ 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.
Fixes: 9a393b5d5988ea4e (tap: tap as an independent module) Signed-off-by: Girish Moodalbail girish.moodalbail@oracle.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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(-)
--- a/drivers/net/ipvlan/ipvtap.c +++ b/drivers/net/ipvlan/ipvtap.c @@ -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;
--- a/drivers/net/macvtap.c +++ b/drivers/net/macvtap.c @@ -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;
--- a/drivers/net/tap.c +++ b/drivers/net/tap.c @@ -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; --- a/include/linux/if_tap.h +++ b/include/linux/if_tap.h @@ -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_*/