NFSD: Fix use-after-free warning when doing inter-server copy

The source file nfsd_file is not constructed the same as other
nfsd_file's via nfsd_file_alloc. nfsd_file_put should not be
called to free the object; nfsd_file_put is not the inverse of
kzalloc, instead kfree is called by nfsd4_do_async_copy when done.

Fixes: ce0887ac ("NFSD add nfs4 inter ssc to nfsd4_copy")
Signed-off-by: NDai Ngo <dai.ngo@oracle.com>
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4proc.c

@@ -1299,7 +1299,7 @@ nfsd4_cleanup_inter_ssc(struct vfsmount *ss_mnt, struct nfsd_file *src,
 			struct nfsd_file *dst)
 {
 	nfs42_ssc_close(src->nf_file);
-	nfsd_file_put(src);
+	/* 'src' is freed by nfsd4_do_async_copy */
 	nfsd_file_put(dst);
 	mntput(ss_mnt);
 }