Re: [PATCH net] net: devlink: fix UAF in devlink_compat_running_version()

[Yang Yingliang <yangyingliang@huawei.com>]

Hi,

On 2022/11/22 22:32, Leon Romanovsky wrote:
> On Tue, Nov 22, 2022 at 08:10:48PM +0800, Yang Yingliang wrote:
>> I got a UAF report as following when doing fault injection test:
>>
>> BUG: KASAN: use-after-free in devlink_compat_running_version+0x5b9/0x6a0
>> Read of size 8 at addr ffff88810ac591f0 by task systemd-udevd/458
>>
>> CPU: 2 PID: 458 Comm: systemd-udevd Not tainted 6.1.0-rc5-00155-ga9d2b54dd4e7-dirty #1359
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
>> Call Trace:
>>   <TASK>
>>   kasan_report+0x90/0x190
>>   devlink_compat_running_version+0x5b9/0x6a0
>>   dev_ethtool+0x2ca/0x340
>>   dev_ioctl+0x16c/0xff0
>>   sock_do_ioctl+0x1ae/0x220
>>
>> Allocated by task 456:
>>   kasan_save_stack+0x1c/0x40
>>   kasan_set_track+0x21/0x30
>>   __kasan_kmalloc+0x7e/0x90
>>   __kmalloc+0x59/0x1b0
>>   devlink_alloc_ns+0xf7/0xa10
>>   nsim_drv_probe+0xa8/0x150 [netdevsim]
>>   really_probe+0x1ff/0x660
>>
>> Freed by task 456:
>>   kasan_save_stack+0x1c/0x40
>>   kasan_set_track+0x21/0x30
>>   kasan_save_free_info+0x2a/0x50
>>   __kasan_slab_free+0x102/0x190
>>   __kmem_cache_free+0xca/0x400
>>   nsim_drv_probe.cold.31+0x2af/0xf62 [netdevsim]
>>   really_probe+0x1ff/0x660
>>
>> It happened like this:
>>
>> processor A							processor B
>> nsim_drv_probe()
>>    devlink_alloc_ns()
>>    nsim_dev_port_add_all()
>>      __nsim_dev_port_add() // add eth1 successful
>> 								dev_ethtool()
>> 								  ethtool_get_drvinfo(eth1)
>> 								    netdev_to_devlink_get(eth1)
>> 								      devlink_try_get() // get devlink here
>>      __nsim_dev_port_add() // add eth2 failed, goto error
>>        devlink_free() // it's called in the error path
>> 								  devlink_compat_running_version() <- causes UAF
>>    devlink_register() // it's in normal path, not called yet
>>
>> There is two ports to add in nsim_dev_port_add_all(), if first
>> port is added successful, the devlink is visable and can be get
>> by devlink_try_get() on another cpu, but it is not registered
>> yet. And then the second port is failed to added, in the error
>> path, devlink_free() is called, at last it causes UAF.
>>
>> Add check in devlink_try_get(), if the 'devlink' is not registered
>> it returns NULL to avoid UAF like this case.
>>
>> Fixes: a62fdbbe9403 ("netdevsim: implement ndo_get_devlink_port")
>> Reported-by: Zhengchao Shao <shaozhengchao@huawei.com>
>> Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
>> ---
>>   net/core/devlink.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/net/core/devlink.c b/net/core/devlink.c
>> index 89baa7c0938b..6453ac0558fb 100644
>> --- a/net/core/devlink.c
>> +++ b/net/core/devlink.c
>> @@ -250,6 +250,9 @@ void devlink_put(struct devlink *devlink)
>>   
>>   struct devlink *__must_check devlink_try_get(struct devlink *devlink)
>>   {
>> +	 if (!xa_get_mark(&devlinks, devlink->index, DEVLINK_REGISTERED))
>> +		return NULL;
>> +
> Please fix nsim instead of devlink.
I think if devlink is not registered, it can not be get and used, but there
is no API for driver to check this, can I introduce a new helper name
devlink_is_registered() for driver using.

Thanks,
Yang
>
> Thanks
>
>>   	if (refcount_inc_not_zero(&devlink->refcount))
>>   		return devlink;
>>   	return NULL;
>> -- 
>> 2.25.1
>>
> .