[PATCH net v3] team: fix null-ptr-deref when team device type is changed

[Ziyang Xuan]

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.

Assign eth_header_ops to header_ops of team device when its type is changed
from non-ether to ether to fix the bug.

Fixes: 1d76efe1577b ("team: add support for non-ethernet devices")
Suggested-by: Hangbin Liu <liuhangbin@xxxxxxxxx>
Signed-off-by: Ziyang Xuan <william.xuanziyang@xxxxxxxxxx>
---
v3:
  - Export eth_header_ops to fix modpost error.
v2:
  - Just modify header_ops to eth_header_ops not use ether_setup().
---
 drivers/net/team/team.c | 5 ++++-
 net/ethernet/eth.c      | 1 +
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/net/team/team.c b/drivers/net/team/team.c
index d3dc22509ea5..12fb5f4cff06 100644
--- a/drivers/net/team/team.c
+++ b/drivers/net/team/team.c
@@ -2127,7 +2127,10 @@ static const struct ethtool_ops team_ethtool_ops = {
 static void team_setup_by_port(struct net_device *dev,
 			       struct net_device *port_dev)
 {
-	dev->header_ops	= port_dev->header_ops;
+	if (port_dev->type == ARPHRD_ETHER)
+		dev->header_ops	= &eth_header_ops;
+	else
+		dev->header_ops	= port_dev->header_ops;
 	dev->type = port_dev->type;
 	dev->hard_header_len = port_dev->hard_header_len;
 	dev->needed_headroom = port_dev->needed_headroom;
diff --git a/net/ethernet/eth.c b/net/ethernet/eth.c
index 2edc8b796a4e..157833509adb 100644
--- a/net/ethernet/eth.c
+++ b/net/ethernet/eth.c
@@ -347,6 +347,7 @@ const struct header_ops eth_header_ops ____cacheline_aligned = {
 	.cache_update	= eth_header_cache_update,
 	.parse_protocol	= eth_header_parse_protocol,
 };
+EXPORT_SYMBOL(eth_header_ops);
 
 /**
  * ether_setup - setup Ethernet network device
-- 
2.25.1