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.

Fixes: c5967721e106 ("NFSD: handle GETATTR conflict with write delegation")
Signed-off-by: NeilBrown <[e-mail]>
Reviewed-by: Jeff Layton <[e-mail]>
Signed-off-by: Chuck Lever <[e-mail]>

fs/nfsd/nfs4state.c

···
 			 */
 			if (type == F_RDLCK)
 				break;
-			goto break_lease;
+
+			nfsd_stats_wdeleg_getattr_inc(nn);
+			spin_unlock(&ctx->flc_lock);
+
+			status = nfserrno(nfsd_open_break_lease(inode, NFSD_MAY_READ));
+			if (status != nfserr_jukebox ||
+			    !nfsd_wait_for_delegreturn(rqstp, inode))
+				return status;
+			return 0;
 		}
 		if (type == F_WRLCK) {
 			struct nfs4_delegation *dp = fl->c.flc_owner;
···
 				spin_unlock(&ctx->flc_lock);
 				return 0;
 			}
-break_lease:
 			nfsd_stats_wdeleg_getattr_inc(nn);
 			dp = fl->c.flc_owner;
 			refcount_inc(&dp->dl_stid.sc_count);