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
