[NFS]: Check that the server returns a valid regular file to our OPEN request

 Since it appears that some servers don't...
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/dir.c

@@ -957,10 +957,12 @@ static struct dentry *nfs_atomic_lookup(struct inode *dir, struct dentry *dentry
 				res = NULL;
 				goto out;
 			/* This turned out not to be a regular file */
+			case -EISDIR:
+			case -ENOTDIR:
+				goto no_open;
 			case -ELOOP:
 				if (!(nd->intent.open.flags & O_NOFOLLOW))
 					goto no_open;
-			/* case -EISDIR: */
 			/* case -EINVAL: */
 			default:
 				goto out;

fs/nfs/nfs4proc.c

@@ -419,6 +419,22 @@ static int _nfs4_proc_open(struct inode *dir, struct nfs4_state_owner  *sp, stru
 	o_arg->clientid = sp->so_client->cl_clientid;
 
 	status = rpc_call_sync(server->client, &msg, RPC_TASK_NOINTR);
+	if (status == 0) {
+		/* OPEN on anything except a regular file is disallowed in NFSv4 */
+		switch (o_res->f_attr->mode & S_IFMT) {
+			case S_IFREG:
+				break;
+			case S_IFLNK:
+				status = -ELOOP;
+				break;
+			case S_IFDIR:
+				status = -EISDIR;
+				break;
+			default:
+				status = -ENOTDIR;
+		}
+	}
+
 	nfs_increment_open_seqid(status, o_arg->seqid);
 	if (status != 0)
 		goto out;