nfsd: memory corruption in nfsd4_lock()

New struct nfsd4_blocked_lock allocated in find_or_allocate_block()
does not initialized nbl_list and nbl_lru.
If conflock allocation fails rollback can call list_del_init()
access uninitialized fields and corrupt memory.

v2: just initialize nbl_list and nbl_lru right after nbl allocation.

Fixes: 76d348fa ("nfsd: have nfsd4_lock use blocking locks for v4.1+ lock")
Signed-off-by: NVasily Averin <vvs@virtuozzo.com>
Reviewed-by: NJeff Layton <jlayton@kernel.org>
Signed-off-by: NChuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfs4state.c

@@ -267,6 +267,8 @@ find_or_allocate_block(struct nfs4_lockowner *lo, struct knfsd_fh *fh,
 	if (!nbl) {
 		nbl= kmalloc(sizeof(*nbl), GFP_KERNEL);
 		if (nbl) {
+			INIT_LIST_HEAD(&nbl->nbl_list);
+			INIT_LIST_HEAD(&nbl->nbl_lru);
 			fh_copy_shallow(&nbl->nbl_fh, fh);
 			locks_init_lock(&nbl->nbl_lock);
 			nfsd4_init_cb(&nbl->nbl_cb, lo->lo_owner.so_client,