Date:   Wed, 24 Nov 2021 08:50:18 -0400
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        syzbot+e4df4e1389e28972e955@syzkaller.appspotmail.com,
        Ziyang Xuan <william.xuanziyang@huawei.com>,
        "David S. Miller" <davem@davemloft.net>,
        Sasha Levin <sashal@kernel.org>
Subject: Re: [PATCH 4.14 181/251] net: vlan: fix a UAF in vlan_dev_real_dev()
Message-ID: <20211124125018.GG4670@nvidia.com>
References: <20211124115710.214900256@linuxfoundation.org>
 <20211124115716.547727004@linuxfoundation.org>
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On Wed, Nov 24, 2021 at 12:57:03PM +0100, Greg Kroah-Hartman wrote:
> From: Ziyang Xuan <william.xuanziyang@huawei.com>
> 
> [ Upstream commit 563bcbae3ba233c275c244bfce2efe12938f5363 ]
> 
> The real_dev of a vlan net_device may be freed after
> unregister_vlan_dev(). Access the real_dev continually by
> vlan_dev_real_dev() will trigger the UAF problem for the
> real_dev like following:
> 
> ==================================================================
> BUG: KASAN: use-after-free in vlan_dev_real_dev+0xf9/0x120
> Call Trace:
>  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
> ...
> 
> 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
> ...
> 
> Move the put_device(real_dev) to vlan_dev_free(). Ensure
> real_dev not be freed before vlan_dev unregistered.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Reported-by: syzbot+e4df4e1389e28972e955@syzkaller.appspotmail.com
> Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: David S. Miller <davem@davemloft.net>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
>  net/8021q/vlan.c     | 3 ---
>  net/8021q/vlan_dev.c | 3 +++
>  2 files changed, 3 insertions(+), 3 deletions(-)

This patch is known to be broken, it should not be backported

Jason