um: Add winch to winch_handlers before registering winch IRQ

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: um: Add winch to winch_handlers before registering winch IRQ Registering a winch IRQ is racy, an interrupt may occur before the winch is added to the winch_handlers list. If that happens, register_winch_irq() adds to that list a winch that is scheduled to be (or has already been) freed, causing a panic later in winch_cleanup(). Avoid the race by adding the winch to the winch_handlers list before registering the IRQ, and rolling back if um_request_irq() fails.

References

• https://git.kernel.org/stable/c/66ea9a7c6824821476914bed21a476cd20094f33
• https://git.kernel.org/stable/c/dc1ff95602ee908fcd7d8acee7a0dadb61b1a0c0
• https://git.kernel.org/stable/c/351d1a64544944b44732f6a64ed65573b00b9e14
• https://git.kernel.org/stable/c/31960d991e43c8d6dc07245f19fc13398e90ead2
• https://git.kernel.org/stable/c/0c02d425a2fbe52643a5859a779db0329e7dddd4
• https://git.kernel.org/stable/c/434a06c38ee1217a8baa0dd7c37cc85d50138fb0
• https://git.kernel.org/stable/c/73b8e21f76c7dda4905655d2e2c17dc5a73b87f1
• https://git.kernel.org/stable/c/a0fbbd36c156b9f7b2276871d499c9943dfe5101