expat/SOURCES/expat-2.2.5-Protect-against-malicious-namespace-declarations.patch

commit fd5473ef5873048eadef344a1f16f71ad8eefe99
Author: Tomas Korbar <tkorbar@redhat.com>
Date:   Mon Mar 14 12:17:41 2022 +0100

    Protect against malicious namespace declarations

diff --git a/lib/xmlparse.c b/lib/xmlparse.c
index 581b9a4..6f3510b 100644
--- a/lib/xmlparse.c
+++ b/lib/xmlparse.c
@@ -661,8 +661,7 @@ XML_ParserCreate(const XML_Char *encodingName)
 XML_Parser XMLCALL
 XML_ParserCreateNS(const XML_Char *encodingName, XML_Char nsSep)
 {
-  XML_Char tmp[2];
-  *tmp = nsSep;
+  XML_Char tmp[2] = {nsSep, 0};
   return XML_ParserCreate_MM(encodingName, NULL, tmp);
 }
 
@@ -1288,8 +1287,7 @@ XML_ExternalEntityParserCreate(XML_Parser oldParser,
      would be otherwise.
   */
   if (parser->m_ns) {
-    XML_Char tmp[2];
-    *tmp = parser->m_namespaceSeparator;
+    XML_Char tmp[2] = {parser->m_namespaceSeparator, 0};
     parser = parserCreate(encodingName, &parser->m_mem, tmp, newDtd);
   }
   else {
@@ -3640,6 +3638,117 @@ storeAtts(XML_Parser parser, const ENCODING *enc,
   return XML_ERROR_NONE;
 }
 
+static XML_Bool
+is_rfc3986_uri_char(XML_Char candidate) {
+  // For the RFC 3986 ANBF grammar see
+  // https://datatracker.ietf.org/doc/html/rfc3986#appendix-A
+
+  switch (candidate) {
+  // From rule "ALPHA" (uppercase half)
+  case 'A':
+  case 'B':
+  case 'C':
+  case 'D':
+  case 'E':
+  case 'F':
+  case 'G':
+  case 'H':
+  case 'I':
+  case 'J':
+  case 'K':
+  case 'L':
+  case 'M':
+  case 'N':
+  case 'O':
+  case 'P':
+  case 'Q':
+  case 'R':
+  case 'S':
+  case 'T':
+  case 'U':
+  case 'V':
+  case 'W':
+  case 'X':
+  case 'Y':
+  case 'Z':
+
+  // From rule "ALPHA" (lowercase half)
+  case 'a':
+  case 'b':
+  case 'c':
+  case 'd':
+  case 'e':
+  case 'f':
+  case 'g':
+  case 'h':
+  case 'i':
+  case 'j':
+  case 'k':
+  case 'l':
+  case 'm':
+  case 'n':
+  case 'o':
+  case 'p':
+  case 'q':
+  case 'r':
+  case 's':
+  case 't':
+  case 'u':
+  case 'v':
+  case 'w':
+  case 'x':
+  case 'y':
+  case 'z':
+
+  // From rule "DIGIT"
+  case '0':
+  case '1':
+  case '2':
+  case '3':
+  case '4':
+  case '5':
+  case '6':
+  case '7':
+  case '8':
+  case '9':
+
+  // From rule "pct-encoded"
+  case '%':
+
+  // From rule "unreserved"
+  case '-':
+  case '.':
+  case '_':
+  case '~':
+
+  // From rule "gen-delims"
+  case ':':
+  case '/':
+  case '?':
+  case '#':
+  case '[':
+  case ']':
+  case '@':
+
+  // From rule "sub-delims"
+  case '!':
+  case '$':
+  case '&':
+  case '\'':
+  case '(':
+  case ')':
+  case '*':
+  case '+':
+  case ',':
+  case ';':
+  case '=':
+    return XML_TRUE;
+
+  default:
+    return XML_FALSE;
+  }
+}
+
 /* addBinding() overwrites the value of prefix->binding without checking.
    Therefore one must keep track of the old value outside of addBinding().
 */
@@ -3700,6 +3809,29 @@ addBinding(XML_Parser parser, PREFIX *prefix, const ATTRIBUTE_ID *attId,
     if (!mustBeXML && isXMLNS
         && (len > xmlnsLen || uri[len] != xmlnsNamespace[len]))
       isXMLNS = XML_FALSE;
+
+    // NOTE: While Expat does not validate namespace URIs against RFC 3986
+    //       today (and is not REQUIRED to do so with regard to the XML 1.0
+    //       namespaces specification) we have to at least make sure, that
+    //       the application on top of Expat (that is likely splitting expanded
+    //       element names ("qualified names") of form
+    //       "[uri sep] local [sep prefix] '\0'" back into 1, 2 or 3 pieces
+    //       in its element handler code) cannot be confused by an attacker
+    //       putting additional namespace separator characters into namespace
+    //       declarations.  That would be ambiguous and not to be expected.
+    //
+    //       While the HTML API docs of function XML_ParserCreateNS have been
+    //       advising against use of a namespace separator character that can
+    //       appear in a URI for >20 years now, some widespread applications
+    //       are using URI characters (':' (colon) in particular) for a
+    //       namespace separator, in practice.  To keep these applications
+    //       functional, we only reject namespaces URIs containing the
+    //       application-chosen namespace separator if the chosen separator
+    //       is a non-URI character with regard to RFC 3986.
+    if (parser->m_ns && (uri[len] == parser->m_namespaceSeparator)
+        && ! is_rfc3986_uri_char(uri[len])) {
+      return XML_ERROR_SYNTAX;
+    }
   }
   isXML = isXML && len == xmlLen;
   isXMLNS = isXMLNS && len == xmlnsLen;
diff --git a/tests/runtests.c b/tests/runtests.c
index ecc6f47..eabd55d 100644
--- a/tests/runtests.c
+++ b/tests/runtests.c
@@ -7950,6 +7950,38 @@ START_TEST(test_ns_double_colon_doctype)
 }
 END_TEST
 
+START_TEST(test_ns_separator_in_uri) {
+  struct test_case {
+    enum XML_Status expectedStatus;
+    const char *doc;
+    XML_Char namesep;
+  };
+  struct test_case cases[] = {
+      {XML_STATUS_OK, "<doc xmlns='one_two' />", XCS('\n')},
+      {XML_STATUS_ERROR, "<doc xmlns='one&#x0A;two' />", XCS('\n')},
+      {XML_STATUS_OK, "<doc xmlns='one:two' />", XCS(':')},
+  };
+
+  size_t i = 0;
+  size_t failCount = 0;
+  for (; i < sizeof(cases) / sizeof(cases[0]); i++) {
+    XML_Parser parser = XML_ParserCreateNS(NULL, cases[i].namesep);
+    XML_SetElementHandler(parser, dummy_start_element, dummy_end_element);
+    if (XML_Parse(parser, cases[i].doc, (int)strlen(cases[i].doc),
+                  /*isFinal*/ XML_TRUE)
+        != cases[i].expectedStatus) {
+      failCount++;
+    }
+    XML_ParserFree(parser);
+  }
+
+  if (failCount) {
+    fail("Namespace separator handling is broken");
+  }
+}
+END_TEST
+
+
 /* Control variable; the number of times duff_allocator() will successfully allocate */
 #define ALLOC_ALWAYS_SUCCEED (-1)
 #define REALLOC_ALWAYS_SUCCEED (-1)
@@ -12290,6 +12322,7 @@ make_suite(void)
     tcase_add_test(tc_namespace, test_ns_utf16_doctype);
     tcase_add_test(tc_namespace, test_ns_invalid_doctype);
     tcase_add_test(tc_namespace, test_ns_double_colon_doctype);
+    tcase_add_test(tc_namespace, test_ns_separator_in_uri);
 
     suite_add_tcase(s, tc_misc);
     tcase_add_checked_fixture(tc_misc, NULL, basic_teardown);