In the Linux kernel, the following vulnerability has been resolved:

usb: atm: ueagle-atm: wait for pre-firmware load in .disconnect()

ueagle-atm uses the asynchronous request_firmware_nowait() in .probe(),
but does not wait for its completion, not even in .disconnect(); so, if the
device is unplugged meanwhile, its teardown runs concurrently with that.

Even though this inconsistency is worth addressing on its own, it has also
triggered several bug reports in syzbot over the years (some auto-closed)
where the firmware sysfs fallback mechanism (CONFIG_FW_LOADER_USER_HELPER)
creates a firmware subdirectory in the device directory during its removal,
which might hit unexpected conditions in kernfs, apparently, depending at
which point the add and remove operations raced. (See links.)

The pattern is:

usb ?-?: Direct firmware load for ueagle-atm/eagle?.fw failed with error -2
usb ?-?: Falling back to sysfs fallback for: ueagle-atm/eagle?.fw
<ERROR>
Call trace:
 ...
 kernfs_create_dir_ns
 sysfs_create_dir_ns
 create_dir
 kobject_add_internal
 kobject_add_varg
 kobject_add
 class_dir_create_and_add
 get_device_parent
 device_add
 fw_load_sysfs_fallback
 fw_load_from_user_helper
 firmware_fallback_sysfs
 _request_firmware
 request_firmware_work_func
 ...

(Some variations are observed, after fw_load_sysfs_fallback(), e.g., [1].)

While the kernfs side is being looked at, the ueagle-atm side can be fixed
by waiting for the pre-firmware load in the .disconnect() handler.

This change has a similar approach to previous work by Andrey Tsygunka [2]
(wait_for_completion() in .disconnect()), but it is relatively different in
design/implementation; using the Originally-by tag for credit assignment.

This has been tested with:
- synthetic reproducer to check the error path;
- USB gadget (virtual device) to check the firmware upload path;
- QEMU device emulator to check the device ID re-enumeration path;
(The latter two were written by Claude; no other code/text in this commit.)

Links (year first reported):
 2025 https://syzb

https://git.kernel.org/stable/c/509b51327320bdeaef1969248177a446ded073ab

https://git.kernel.org/stable/c/76861031b43a18065d13f9ffb8595d25c7576005

https://git.kernel.org/stable/c/bbfedc84714064ea4845e6b76f96316eb5bb65d8

https://git.kernel.org/stable/c/c581e30ae5b332d8acef64475a211b3f82099941

https://git.kernel.org/stable/c/d85f19aaef42a03e3e4765d659c761c8750a7f23

https://git.kernel.org/stable/c/ddcdac47e1f2651c7be60e299f98faf981522797

https://git.kernel.org/stable/c/e2674dfbed8a30d57e2bc872c4bfa6c3eec918bf

https://git.kernel.org/stable/c/f2a6abc670104fc3e383ee3b1cf35c070485e3df

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