Describe CVE-2021-47582.
What is CVE-2021-47582?
In the Linux kernel, the following vulnerability has been resolved:

USB: core: Make do_proc_control() and do_proc_bulk() killable

The USBDEVFS_CONTROL and USBDEVFS_BULK ioctls invoke
usb_start_wait_urb(), which contains an uninterruptible wait with a
user-specified timeout value.  If timeout value is very large and the
device being accessed does not respond in a reasonable amount of time,
the kernel will complain about "Task X blocked for more than N
seconds", as found in testing by syzbot:

INFO: task syz-executor.0:8700 blocked for more than 143 seconds.
      Not tainted 5.14.0-rc7-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor.0  state:D stack:23192 pid: 8700 ppid:  8455 flags:0x00004004
Call Trace:
 context_switch kernel/sched/core.c:4681 [inline]
 __schedule+0xc07/0x11f0 kernel/sched/core.c:5938
 schedule+0x14b/0x210 kernel/sched/core.c:6017
 schedule_timeout+0x98/0x2f0 kernel/time/timer.c:1857
 do_wait_for_common+0x2da/0x480 kernel/sched/completion.c:85
 __wait_for_common kernel/sched/completion.c:106 [inline]
 wait_for_common kernel/sched/completion.c:117 [inline]
 wait_for_completion_timeout+0x46/0x60 kernel/sched/completion.c:157
 usb_start_wait_urb+0x167/0x550 drivers/usb/core/message.c:63
 do_proc_bulk+0x978/0x1080 drivers/usb/core/devio.c:1236
 proc_bulk drivers/usb/core/devio.c:1273 [inline]
 usbdev_do_ioctl drivers/usb/core/devio.c:2547 [inline]
 usbdev_ioctl+0x3441/0x6b10 drivers/usb/core/devio.c:2713
...

To fix this problem, this patch replaces usbfs's calls to
usb_control_msg() and usb_bulk_msg() with special-purpose code that
does essentially the same thing (as recommended in the comment for
usb_start_wait_urb()), except that it always uses a killable wait and
it uses GFP_KERNEL rather than GFP_NOIO..