manifest: fix out-of-bounds read of corrupted manifest entry stable 4.7.2

manifest: fix out-of-bounds read of corrupted manifest entry

Spotted by ASAN.

--- a/mercurial/cext/manifest.c	Wed Sep 05 21:32:45 2018 +0900
+++ b/mercurial/cext/manifest.c	Wed Sep 05 21:23:29 2018 +0900
@@ -51,7 +51,12 @@
 {
 	char *s = l->start;
 	ssize_t llen = pathlen(l);
-	PyObject *hash = unhexlify(s + llen + 1, 40);
+	PyObject *hash;
+	if (llen + 1 + 40 + 1 > l->len) { /* path '\0' hash '\n' */
+		PyErr_SetString(PyExc_ValueError, "manifest line too short");
+		return NULL;
+	}
+	hash = unhexlify(s + llen + 1, 40);
 	if (!hash) {
 		return NULL;
 	}
@@ -249,10 +254,13 @@
 	pl = pathlen(l);
 	path = PyBytes_FromStringAndSize(l->start, pl);
 	hash = nodeof(l);
+	if (!path || !hash) {
+		goto done;
+	}
 	consumed = pl + 41;
 	flags = PyBytes_FromStringAndSize(l->start + consumed,
 					   l->len - consumed - 1);
-	if (!path || !hash || !flags) {
+	if (!flags) {
 		goto done;
 	}
 	ret = PyTuple_Pack(3, path, hash, flags);