um: Add winch to winch_handlers before registering winch IRQ

stable inclusion
from stable-v4.19.316
commit 66ea9a7c6824821476914bed21a476cd20094f33
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/IA7YJR
CVE: CVE-2024-39292

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=66ea9a7c6824821476914bed21a476cd20094f33



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[ Upstream commit a0fbbd36c156b9f7b2276871d499c9943dfe5101 ]

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.

Fixes: 42a359e3 ("uml: SIGIO support cleanup")
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Reviewed-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Chen Zhongjin <chenzhongjin@huawei.com>