CVE-2021-47299: In the Linux kernel, the following vulnerability has been resolved:  xdp, net: Fix use-after-free in bpf_xdp_link_release  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 ---truncated---