NFS4: avoid underflow when converting error to pointer.

In nfs4_create_sec_client, 'flavor' can hold a negative error code (returned from nfs4_negotiate_security), even though it is an 'enum' and hence unsigned.

The code is careful to cast it to an (int) before testing if it is negative, however it doesn't cast to an (int) before calling ERR_PTR.

On a machine where "void*" is larger than "int", this results in the unsigned equivalent of -1 (e.g. 0xffffffff) being converted to a pointer. Subsequent code determines that this is not negative, and so dereferences it with predictable results.

So: cast 'flavor' to a (signed) int before passing to ERR_PTR.

index 017b4b0..9bc56f6 100644
@@ -198,7 +198,7 @@ struct rpc_clnt *nfs4_create_sec_client(struct rpc_clnt *clnt, struct inode *ino
 
 	flavor = nfs4_negotiate_security(inode, name);
 	if ((int)flavor < 0)
-		return ERR_PTR(flavor);
+		return ERR_PTR((int)flavor);
 
 	clone = rpc_clone_client(clnt);
 	if (IS_ERR(clone))