nfsd: Initialize ssc before laundromat_work to prevent NULL dereference

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: nfsd: Initialize ssc before laundromat_work to prevent NULL dereference In nfs4_state_start_net(), laundromat_work may access nfsd_ssc through nfs4_laundromat -> nfsd4_ssc_expire_umount. If nfsd_ssc isn't initialized, this can cause NULL pointer dereference. Normally the delayed start of laundromat_work allows sufficient time for nfsd_ssc initialization to complete. However, when the kernel waits too long for userspace responses (e.g. in nfs4_state_start_net -> nfsd4_end_grace -> nfsd4_record_grace_done -> nfsd4_cld_grace_done -> cld_pipe_upcall -> __cld_pipe_upcall -> wait_for_completion path), the delayed work may start before nfsd_ssc initialization finishes. Fix this by moving nfsd_ssc initialization before starting laundromat_work.

References

• https://git.kernel.org/stable/c/deaeb74ae9318252829c59a84a7d2316fc335660
• https://git.kernel.org/stable/c/0fccf5f01ed28725cc313a66ca1247eef911d55e
• https://git.kernel.org/stable/c/a97668ec6d73dab237cd1c15efe012a10090a4ed
• https://git.kernel.org/stable/c/5060e1a5fef184bd11d298e3f0ee920d96a23236
• https://git.kernel.org/stable/c/d622c2ee6c08147ab8c9b9e37d93b6e95d3258e0
• https://git.kernel.org/stable/c/83ac1ba8ca102ab5c0ed4351f8ac6e74ac4d5d64
• https://git.kernel.org/stable/c/b31da62889e6d610114d81dc7a6edbcaa503fcf8