nfsd: fix nfsd4_deleg_getattr_conflict in presence of third party lease

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: nfsd: fix nfsd4_deleg_getattr_conflict in presence of third party lease It is not safe to dereference fl->c.flc_owner without first confirming fl->fl_lmops is the expected manager. nfsd4_deleg_getattr_conflict() tests fl_lmops but largely ignores the result and assumes that flc_owner is an nfs4_delegation anyway. This is wrong. With this patch we restore the "!= &nfsd_lease_mng_ops" case to behave as it did before the change mentioned below. This is the same as the current code, but without any reference to a possible delegation.

References

• https://git.kernel.org/stable/c/1b46a871e980e3daa16fd5e77539966492e8910a
• https://git.kernel.org/stable/c/40927f3d0972bf86357a32a5749be71a551241b6