NFSv4.2: fix reference count leaks in _nfs42_proc_copy_notify()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: NFSv4.2: fix reference count leaks in _nfs42_proc_copy_notify() [You don't often get email from xiongx18@fudan.edu.cn. Learn why this is important at http://aka.ms/LearnAboutSenderIdentification.] The reference counting issue happens in two error paths in the function _nfs42_proc_copy_notify(). In both error paths, the function simply returns the error code and forgets to balance the refcount of object `ctx`, bumped by get_nfs_open_context() earlier, which may cause refcount leaks. Fix it by balancing refcount of the `ctx` object before the function returns in both error paths.

References

• https://git.kernel.org/stable/c/9b9feec97c1fc7dd9bb69f62c4905cddf1801599
• https://git.kernel.org/stable/c/b37f482ba9f0e6382c188e3fccf6c4b2fdc938eb
• https://git.kernel.org/stable/c/fb73bf6305f4eb8f0cf9a61ee874d55f019d6dc4
• https://git.kernel.org/stable/c/f46f632f9cfae4b2e3635fa58840a8ec584c42e3
• https://git.kernel.org/stable/c/b7f114edd54326f730a754547e7cfb197b5bc132