Re: [PATCH net v4] xdp, net: fix use-after-free in bpf_xdp_link_release

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On Mon, Jul 12, 2021 at 4:22 PM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Fri, Jul 9, 2021 at 8:16 PM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote:
> >
> > The problem occurs between dev_get_by_index() and dev_xdp_attach_link().
> > At this point, dev_xdp_uninstall() is called. Then xdp link will not be
> > detached automatically when dev is released. But link->dev already
> > points to dev, when xdp link is released, dev will still be accessed,
> > but dev has been released.
> >
> > dev_get_by_index()        |
> > link->dev = dev           |
> >                           |      rtnl_lock()
> >                           |      unregister_netdevice_many()
> >                           |          dev_xdp_uninstall()
> >                           |      rtnl_unlock()
> > rtnl_lock();              |
> > dev_xdp_attach_link()     |
> > rtnl_unlock();            |
> >                           |      netdev_run_todo() // dev released
> > bpf_xdp_link_release()    |
> >     /* access dev.        |
> >        use-after-free */  |
> >
> > [   45.966867] BUG: KASAN: use-after-free in bpf_xdp_link_release+0x3b8/0x3d0
> > [   45.967619] Read of size 8 at addr ffff00000f9980c8 by task a.out/732
> > [   45.968297]
> > [   45.968502] CPU: 1 PID: 732 Comm: a.out Not tainted 5.13.0+ #22
> > [   45.969222] Hardware name: linux,dummy-virt (DT)
> > [   45.969795] Call trace:
> > [   45.970106]  dump_backtrace+0x0/0x4c8
> > [   45.970564]  show_stack+0x30/0x40
> > [   45.970981]  dump_stack_lvl+0x120/0x18c
> > [   45.971470]  print_address_description.constprop.0+0x74/0x30c
> > [   45.972182]  kasan_report+0x1e8/0x200
> > [   45.972659]  __asan_report_load8_noabort+0x2c/0x50
> > [   45.973273]  bpf_xdp_link_release+0x3b8/0x3d0
> > [   45.973834]  bpf_link_free+0xd0/0x188
> > [   45.974315]  bpf_link_put+0x1d0/0x218
> > [   45.974790]  bpf_link_release+0x3c/0x58
> > [   45.975291]  __fput+0x20c/0x7e8
> > [   45.975706]  ____fput+0x24/0x30
> > [   45.976117]  task_work_run+0x104/0x258
> > [   45.976609]  do_notify_resume+0x894/0xaf8
> > [   45.977121]  work_pending+0xc/0x328
> > [   45.977575]
> > [   45.977775] The buggy address belongs to the page:
> > [   45.978369] page:fffffc00003e6600 refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x4f998
> > [   45.979522] flags: 0x7fffe0000000000(node=0|zone=0|lastcpupid=0x3ffff)
> > [   45.980349] raw: 07fffe0000000000 fffffc00003e6708 ffff0000dac3c010 0000000000000000
> > [   45.981309] raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
> > [   45.982259] page dumped because: kasan: bad access detected
> > [   45.982948]
> > [   45.983153] Memory state around the buggy address:
> > [   45.983753]  ffff00000f997f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> > [   45.984645]  ffff00000f998000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> > [   45.985533] >ffff00000f998080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> > [   45.986419]                                               ^
> > [   45.987112]  ffff00000f998100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> > [   45.988006]  ffff00000f998180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> > [   45.988895] ==================================================================
> > [   45.989773] Disabling lock debugging due to kernel taint
> > [   45.990552] Kernel panic - not syncing: panic_on_warn set ...
> > [   45.991166] CPU: 1 PID: 732 Comm: a.out Tainted: G    B             5.13.0+ #22
> > [   45.991929] Hardware name: linux,dummy-virt (DT)
> > [   45.992448] Call trace:
> > [   45.992753]  dump_backtrace+0x0/0x4c8
> > [   45.993208]  show_stack+0x30/0x40
> > [   45.993627]  dump_stack_lvl+0x120/0x18c
> > [   45.994113]  dump_stack+0x1c/0x34
> > [   45.994530]  panic+0x3a4/0x7d8
> > [   45.994930]  end_report+0x194/0x198
> > [   45.995380]  kasan_report+0x134/0x200
> > [   45.995850]  __asan_report_load8_noabort+0x2c/0x50
> > [   45.996453]  bpf_xdp_link_release+0x3b8/0x3d0
> > [   45.997007]  bpf_link_free+0xd0/0x188
> > [   45.997474]  bpf_link_put+0x1d0/0x218
> > [   45.997942]  bpf_link_release+0x3c/0x58
> > [   45.998429]  __fput+0x20c/0x7e8
> > [   45.998833]  ____fput+0x24/0x30
> > [   45.999247]  task_work_run+0x104/0x258
> > [   45.999731]  do_notify_resume+0x894/0xaf8
> > [   46.000236]  work_pending+0xc/0x328
> > [   46.000697] SMP: stopping secondary CPUs
> > [   46.001226] Dumping ftrace buffer:
> > [   46.001663]    (ftrace buffer empty)
> > [   46.002110] Kernel Offset: disabled
> > [   46.002545] CPU features: 0x00000001,23202c00
> > [   46.003080] Memory Limit: none
> >
> > Fixes: aa8d3a716b59db6c ("bpf, xdp: Add bpf_link-based XDP attachment API")
> > Reported-by: Abaci <abaci@xxxxxxxxxxxxxxxxx>
> > Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> > Reviewed-by: Dust Li <dust.li@xxxxxxxxxxxxxxxxx>
> > ---
>
> LGTM, thanks for the fix!
>
> Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>

Applied. Thanks



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