From: Maks Verver <maks@verver.ch>
Date: Tue, 8 Apr 2025 13:13:55 +0200
Subject: [PATCH 2/2] [CVE-2025-32414] python: Read at most len/4 characters.

Fixes #889 by reserving space in the buffer for UTF-8 encoding of text.

Index: libxml2-2.9.10+dfsg/python/libxml.c
===================================================================
--- libxml2-2.9.10+dfsg.orig/python/libxml.c	2025-04-28 12:34:16.797639445 +0200
+++ libxml2-2.9.10+dfsg/python/libxml.c	2025-04-28 12:34:16.793639446 +0200
@@ -286,7 +286,9 @@
 #endif
     file = (PyObject *) context;
     if (file == NULL) return(-1);
-    ret = PyEval_CallMethod(file, (char *) "read", (char *) "(i)", len);
+    /* When read() returns a string, the length is in characters not bytes, so
+       request at most len / 4 characters to leave space for UTF-8 encoding. */
+    ret = PyEval_CallMethod(file, (char *) "read", (char *) "(i)", len / 4);
     if (ret == NULL) {
 	printf("xmlPythonFileReadRaw: result is NULL\n");
 	return(-1);
@@ -321,10 +323,12 @@
 	Py_DECREF(ret);
 	return(-1);
     }
-    if (lenread > len)
-	memcpy(buffer, data, len);
-    else
-	memcpy(buffer, data, lenread);
+    if (lenread < 0 || lenread > len) {
+	printf("xmlPythonFileReadRaw: invalid lenread\n");
+	Py_DECREF(ret);
+	return(-1);
+    }
+    memcpy(buffer, data, lenread);
     Py_DECREF(ret);
     return(lenread);
 }
@@ -351,7 +355,9 @@
 #endif
     file = (PyObject *) context;
     if (file == NULL) return(-1);
-    ret = PyEval_CallMethod(file, (char *) "io_read", (char *) "(i)", len);
+    /* When read() returns a string, the length is in characters not bytes, so
+       request at most len / 4 characters to leave space for UTF-8 encoding. */
+    ret = PyEval_CallMethod(file, (char *) "io_read", (char *) "(i)", len / 4);
     if (ret == NULL) {
 	printf("xmlPythonFileRead: result is NULL\n");
 	return(-1);
@@ -386,10 +392,12 @@
 	Py_DECREF(ret);
 	return(-1);
     }
-    if (lenread > len)
-	memcpy(buffer, data, len);
-    else
-	memcpy(buffer, data, lenread);
+    if (lenread < 0 || lenread > len) {
+	printf("xmlPythonFileRead: invalid lenread\n");
+	Py_DECREF(ret);
+	return(-1);
+    }
+    memcpy(buffer, data, lenread);
     Py_DECREF(ret);
     return(lenread);
 }