A null dereference was observed when a sysctl was being set
from userspace and rmnet was stuck trying to complete some actions
in the NETDEV_REGISTER callback. This is because the real_dev is set
only after the device registration handler completes.
sysctl call stack -
<6> Unable to handle kernel NULL pointer dereference at
virtual address 00000108
<2> pc : rmnet_vnd_get_iflink+0x1c/0x28
<2> lr : dev_get_iflink+0x2c/0x40
<2> rmnet_vnd_get_iflink+0x1c/0x28
<2> inet6_fill_ifinfo+0x15c/0x234
<2> inet6_ifinfo_notify+0x68/0xd4
<2> ndisc_ifinfo_sysctl_change+0x1b8/0x234
<2> proc_sys_call_handler+0xac/0x100
<2> proc_sys_write+0x3c/0x4c
<2> __vfs_write+0x54/0x14c
<2> vfs_write+0xcc/0x188
<2> SyS_write+0x60/0xc0
<2> el0_svc_naked+0x34/0x38
device register call stack -
<2> notifier_call_chain+0x84/0xbc
<2> raw_notifier_call_chain+0x38/0x48
<2> call_netdevice_notifiers_info+0x40/0x70
<2> call_netdevice_notifiers+0x38/0x60
<2> register_netdevice+0x29c/0x3d8
<2> rmnet_vnd_newlink+0x68/0xe8
<2> rmnet_newlink+0xa0/0x160
<2> rtnl_newlink+0x57c/0x6c8
<2> rtnetlink_rcv_msg+0x1dc/0x328
<2> netlink_rcv_skb+0xac/0x118
<2> rtnetlink_rcv+0x24/0x30
<2> netlink_unicast+0x158/0x1f0
<2> netlink_sendmsg+0x32c/0x338
<2> sock_sendmsg+0x44/0x60
<2> SyS_sendto+0x150/0x1ac
<2> el0_svc_naked+0x34/0x38
Fixes: b752eff5be ("net: qualcomm: rmnet: Implement ndo_get_iflink")
Signed-off-by: Sean Tranchetti <stranche@codeaurora.org>
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
d02854dc19