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

[Leon Romanovsky <leon@kernel.org>]

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.

Thanks

>  	if (refcount_inc_not_zero(&devlink->refcount))
>  		return devlink;
>  	return NULL;
> -- 
> 2.25.1
>