nfsd: fix possible badness in FREE_STATEID

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: nfsd: fix possible badness in FREE_STATEID When multiple FREE_STATEIDs are sent for the same delegation stateid, it can lead to a possible either use-after-free or counter refcount underflow errors. In nfsd4_free_stateid() under the client lock we find a delegation stateid, however the code drops the lock before calling nfs4_put_stid(), that allows another FREE_STATE to find the stateid again. The first one will proceed to then free the stateid which leads to either use-after-free or decrementing already zeroed counter.

References

• https://git.kernel.org/stable/c/7ca9e472ce5c67daa3188a348ece8c02a0765039
• https://git.kernel.org/stable/c/c88c150a467fcb670a1608e2272beeee3e86df6e