In the Linux kernel, the following vulnerability has been resolved:

team: fix null-ptr-deref when team device type is changed

Get a null-ptr-deref bug as follows with reproducer [1].

BUG: kernel NULL pointer dereference, address: 0000000000000228
…
RIP: 0010:vlan_dev_hard_header+0x35/0x140 [8021q]
…
Call Trace:
<TASK>
? __die+0x24/0x70
? page_fault_oops+0x82/0x150
? exc_page_fault+0x69/0x150
? asm_exc_page_fault+0x26/0x30
? vlan_dev_hard_header+0x35/0x140 [8021q]
? vlan_dev_hard_header+0x8e/0x140 [8021q]
neigh_connected_output+0xb2/0x100
ip6_finish_output2+0x1cb/0x520
? nf_hook_slow+0x43/0xc0
? ip6_mtu+0x46/0x80
ip6_finish_output+0x2a/0xb0
mld_sendpack+0x18f/0x250
mld_ifc_work+0x39/0x160
process_one_work+0x1e6/0x3f0
worker_thread+0x4d/0x2f0
? __pfx_worker_thread+0x10/0x10
kthread+0xe5/0x120
? __pfx_kthread+0x10/0x10
ret_from_fork+0x34/0x50
? __pfx_kthread+0x10/0x10
ret_from_fork_asm+0x1b/0x30

[1]
\( teamd -t team0 -d -c '{"runner": {"name": "loadbalance"}}' \) ip link add name t-dummy type dummy
\( ip link add link t-dummy name t-dummy.100 type vlan id 100 \) ip link add name t-nlmon type nlmon
\( ip link set t-nlmon master team0 \) ip link set t-nlmon nomaster
\( ip link set t-dummy up \) ip link set team0 up
\( ip link set t-dummy.100 down \) ip link set t-dummy.100 master team0

When enslave a vlan device to team device and team device type is changed
from non-ether to ether, header_ops of team device is changed to
vlan_header_ops. That is incorrect and will trigger null-ptr-deref
for vlan->real_dev in vlan_dev_hard_header() because team device is not
a vlan device.

Cache eth_header_ops in team_setup(), then assign cached header_ops to
header_ops of team net device when its type is changed from non-ether
to ether to fix the bug.