Re: [PATCH 4.14 181/251] net: vlan: fix a UAF in vlan_dev_real_dev()

[Jason Gunthorpe]

On Wed, Nov 24, 2021 at 02:15:10PM +0100, Greg Kroah-Hartman wrote:
> On Wed, Nov 24, 2021 at 08:50:18AM -0400, Jason Gunthorpe wrote:
> > On Wed, Nov 24, 2021 at 12:57:03PM +0100, Greg Kroah-Hartman wrote:
> > > From: Ziyang Xuan <william.xuanziyang@xxxxxxxxxx>
> > > 
> > > [ 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@xxxxxxxxxxxxxxxxxxxxxxxxx
> > > Signed-off-by: Ziyang Xuan <william.xuanziyang@xxxxxxxxxx>
> > > Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> > > Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
> > > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> > >  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
> 
> It is already in a bunch of branches :(
> 
> What is the upstream revert of this commit in Linus's tree?

It isn't in a Linus released kernel yet, Ziyang and Petr are working
on fixing it.

Jason