From: Girish Moodalbail <girish.moodalb...@oracle.com>
Date: Fri, 27 Oct 2017 00:00:16 -0700
> 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.moodalb...@oracle.com>
Applied and queued up for -stable.
