Re: [PATCH rdma-rc] IB/core: fix a UAF for netdev in netdevice_event process

[Ziyang Xuan (William)]

> On Mon, Oct 25, 2021 at 11:42:58AM +0800, Ziyang Xuan wrote:
>> When a vlan netdev enter netdevice_event process although it is not a
>> roce netdev, it will be passed to netdevice_event_work_handler() to
>> process. In order to hold the netdev of netdevice_event after
>> netdevice_event() return, call dev_hold() to hold the netdev in
>> netdevice_queue_work(). But that did not consider the real_dev of a vlan
>> netdev, the real_dev can be freed within netdevice_event_work_handler()
>> be scheduled. It would trigger the UAF problem for the real_dev like
>> following:
>>
>> ==================================================================
>> BUG: KASAN: use-after-free in vlan_dev_real_dev+0xf9/0x120
>> Read of size 4 at addr ffff88801648a0c4 by task kworker/u8:0/8
>> Workqueue: gid-cache-wq netdevice_event_work_handler
>> Call Trace:
>>  dump_stack_lvl+0xcd/0x134
>>  print_address_description.constprop.0.cold+0x93/0x334
>>  kasan_report.cold+0x83/0xdf
>>  vlan_dev_real_dev+0xf9/0x120
>>  is_eth_port_of_netdev_filter.part.0+0xb1/0x2c0
>>  is_eth_port_of_netdev_filter+0x28/0x40
>>  ib_enum_roce_netdev+0x1a3/0x300
>>  ib_enum_all_roce_netdevs+0xc7/0x140
>>  netdevice_event_work_handler+0x9d/0x210
>> ...
>>
>> Allocated by task 9289:
>>  kasan_save_stack+0x1b/0x40
>>  __kasan_kmalloc+0x9b/0xd0
>>  __kmalloc_node+0x20a/0x330
>>  kvmalloc_node+0x61/0xf0
>>  alloc_netdev_mqs+0x9d/0x1140
>>  rtnl_create_link+0x955/0xb70
>>  __rtnl_newlink+0xe10/0x15b0
>>  rtnl_newlink+0x64/0xa0
>> ...
>>
>> Freed by task 9288:
>>  kasan_save_stack+0x1b/0x40
>>  kasan_set_track+0x1c/0x30
>>  kasan_set_free_info+0x20/0x30
>>  __kasan_slab_free+0xfc/0x130
>>  slab_free_freelist_hook+0xdd/0x240
>>  kfree+0xe4/0x690
>>  kvfree+0x42/0x50
>>  device_release+0x9f/0x240
>>  kobject_put+0x1c8/0x530
>>  put_device+0x1b/0x30
>>  free_netdev+0x370/0x540
>>  ppp_destroy_interface+0x313/0x3d0
>>  ppp_release+0x1bf/0x240
>> ...
>>
>> Hold the real_dev for a vlan netdev in netdevice_event_work_handler()
>> to fix the UAF problem.
>>
>> Fixes: 238fdf48f2b5 ("IB/core: Add RoCE table bonding support")
>> Reported-by: syzbot+e4df4e1389e28972e955@xxxxxxxxxxxxxxxxxxxxxxxxx
>> Signed-off-by: Ziyang Xuan <william.xuanziyang@xxxxxxxxxx>
>> ---
>>  drivers/infiniband/core/roce_gid_mgmt.c | 16 +++++++++++++++-
>>  1 file changed, 15 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/infiniband/core/roce_gid_mgmt.c b/drivers/infiniband/core/roce_gid_mgmt.c
>> index 68197e576433..063dbe72b7c2 100644
>> --- a/drivers/infiniband/core/roce_gid_mgmt.c
>> +++ b/drivers/infiniband/core/roce_gid_mgmt.c
>> @@ -621,6 +621,7 @@ static void netdevice_event_work_handler(struct work_struct *_work)
>>  {
>>  	struct netdev_event_work *work =
>>  		container_of(_work, struct netdev_event_work, work);
>> +	struct net_device *real_dev;
>>  	unsigned int i;
>>  
>>  	for (i = 0; i < ARRAY_SIZE(work->cmds) && work->cmds[i].cb; i++) {
>> @@ -628,6 +629,12 @@ static void netdevice_event_work_handler(struct work_struct *_work)
>>  					 work->cmds[i].filter_ndev,
>>  					 work->cmds[i].cb,
>>  					 work->cmds[i].ndev);
>> +		real_dev = rdma_vlan_dev_real_dev(work->cmds[i].ndev);
>> +		if (real_dev)
>> +			dev_put(real_dev);
>> +		real_dev = rdma_vlan_dev_real_dev(work->cmds[i].filter_ndev);
>> +		if (real_dev)
>> +			dev_put(real_dev);
>>  		dev_put(work->cmds[i].ndev);
>>  		dev_put(work->cmds[i].filter_ndev);
>>  	}
>> @@ -638,9 +645,10 @@ static void netdevice_event_work_handler(struct work_struct *_work)
>>  static int netdevice_queue_work(struct netdev_event_work_cmd *cmds,
>>  				struct net_device *ndev)
>>  {
>> -	unsigned int i;
>>  	struct netdev_event_work *ndev_work =
>>  		kmalloc(sizeof(*ndev_work), GFP_KERNEL);
>> +	struct net_device *real_dev;
>> +	unsigned int i;
>>  
>>  	if (!ndev_work)
>>  		return NOTIFY_DONE;
>> @@ -653,6 +661,12 @@ static int netdevice_queue_work(struct netdev_event_work_cmd *cmds,
>>  			ndev_work->cmds[i].filter_ndev = ndev;
>>  		dev_hold(ndev_work->cmds[i].ndev);
>>  		dev_hold(ndev_work->cmds[i].filter_ndev);
>> +		real_dev = rdma_vlan_dev_real_dev(ndev_work->cmds[i].ndev);
>> +		if (real_dev)
>> +			dev_hold(real_dev);
>> +		real_dev = rdma_vlan_dev_real_dev(ndev_work->cmds[i].filter_ndev);
>> +		if (real_dev)
>> +			dev_hold(real_dev);
>>  	}
>>  	INIT_WORK(&ndev_work->work, netdevice_event_work_handler);
> 
> Probably, this is the right change, but I don't know well enough that
> part of code. What prevents from "real_dev" to disappear right after
> your call to rdma_vlan_dev_real_dev()?
> 

It is known that free the net_device until its dev_refcnt is one. The
detail realization see netdev_run_todo().The real_dev's dev_refcnt of
a vlan net_device will reach one after unregister_netdevice(&real_dev)
and unregister_vlan_dev(&vlan_ndev, ...) but the dev_refcnt of the vlan
net_device is bigger than one because netdevice_queue_work() will hold
the vlan net_device. So my solution is hold the real_dev too in
netdevice_queue_work().

> Thanks
> 
>>  
>> -- 
>> 2.25.1
>>
> .
>