media: pvrusb2: fix use after free on context disconnection

stable inclusion
from stable-v5.10.209
commit 3233d8bf7893550045682192cb227af7fa3defeb
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I932VV
CVE: CVE-2023-52445

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3233d8bf7893550045682192cb227af7fa3defeb



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[ Upstream commit ded85b0c0edd8f45fec88783d7555a5b982449c1 ]

Upon module load, a kthread is created targeting the
pvr2_context_thread_func function, which may call pvr2_context_destroy
and thus call kfree() on the context object. However, that might happen
before the usb hub_event handler is able to notify the driver. This
patch adds a sanity check before the invalid read reported by syzbot,
within the context disconnection call stack.

Reported-and-tested-by:  <syzbot+621409285c4156a009b3@syzkaller.appspotmail.com>
Closes: https://lore.kernel.org/all/000000000000a02a4205fff8eb92@google.com/



Fixes: e5be15c6 ("V4L/DVB (7711): pvrusb2: Fix race on module unload")
Signed-off-by: Ricardo B. Marliere <ricardo@marliere.net>
Acked-by: Mike Isely <isely@pobox.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Guan Jing <guanjing6@huawei.com>