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

usbip: vudc: fix NULL deref in vep_dequeue()

vep_alloc_request() wasn't initializing vrequest->udc, so cancellations
on the FunctionFS AIO path were arriving in vep_dequeue without a valid
UDC reference.

Since vrequest->udc is never actually properly used anywhere, we opt to
remove it, and update vep_dequeue to obtain a reference to the udc with
ep_to_vudc(), consistent with the other vep_ ops.

AFAICT this bug has existed for ~10 years. Seems that nobody has really
stressed the FunctionFS AIO path on usbip's vudc.

I tested this fix in a QEMU aarch64 guest driving FunctionFS endpoints
via AIO. Before the fix, running `usbip attach` from the host would
cause the guest to oops with the following backtrace:

Call trace:
 vep_dequeue+0x1c/0xe4 (P)
 usb_ep_dequeue+0x14/0x20
 ffs_aio_cancel+0x24/0x34
 __arm64_sys_io_cancel+0xb0/0x124
 do_el0_svc+0x68/0x100
 el0_svc+0x18/0x5c
 el0t_64_sync_handler+0x98/0xdc
 el0t_64_sync+0x154/0x158

https://git.kernel.org/stable/c/0025276175fbbe0dcbf3f84d090b0adee769e9d9

https://git.kernel.org/stable/c/0443e4416aa1ee97748d1ed904eaf3352c60045e

https://git.kernel.org/stable/c/1226293ec9bed3d4cc5b05eeeb811d315ca51652

https://git.kernel.org/stable/c/347b59e9f96719d89b6ef555d02a18ada1a5846f

https://git.kernel.org/stable/c/3750f75f29f99c0223601e2ee73ad084adec47bd

https://git.kernel.org/stable/c/9858c91d9ee6a13c45311569039413729fc9b757

https://git.kernel.org/stable/c/c5371e0b91b24159a3ebaa61e70b0980bcf03c0a

https://git.kernel.org/stable/c/d0ebf9cc7c2ddf95a7cfc654b940bdacb7edde97

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