# erAck: backport of expat CVE-2023-52425 DoS fix

# https://github.com/libexpat/libexpat/commit/34b598c5f594b015c513c73f06e7ced3323edbf1

#

--- firefox-115.9.0/parser/expat/lib/expat.h.expat-CVE-2023-52425	2024-03-11 20:36:11.000000000 +0100

+++ firefox-115.9.0/parser/expat/lib/expat.h	2024-03-13 20:46:45.648505015 +0100

@@ -1045,6 +1045,10 @@ XMLPARSEAPI(const XML_Feature *)

 XML_GetFeatureList(void);

+/* Added in Expat 2.6.0. */

+XMLPARSEAPI(XML_Bool)

+XML_SetReparseDeferralEnabled(XML_Parser parser, XML_Bool enabled);

+

 /* Expat follows the semantic versioning convention.

    See http://semver.org.

 */

--- firefox-115.9.0/parser/expat/lib/internal.h.expat-CVE-2023-52425	2024-03-11 20:36:11.000000000 +0100

+++ firefox-115.9.0/parser/expat/lib/internal.h	2024-03-14 00:14:39.334319725 +0100

@@ -80,6 +80,7 @@

 # endif

 #endif

+#include "expat.h" // so we can use type XML_Parser below

 #ifdef __cplusplus

 extern "C" {

@@ -90,6 +91,9 @@ void

 align_limit_to_full_utf8_characters(const char * from, const char ** fromLimRef);

+extern XML_Bool g_reparseDeferralEnabledDefault; // written ONLY in runtests.c

+extern unsigned int g_parseAttempts;             // used for testing only

+

 #ifdef __cplusplus

 }

 #endif

--- firefox-115.9.0/parser/expat/lib/xmlparse.c.expat-CVE-2023-52425	2024-03-11 20:36:11.000000000 +0100

+++ firefox-115.9.0/parser/expat/lib/xmlparse.c	2024-03-13 22:55:14.844756009 +0100

@@ -6,6 +6,7 @@

 #define _GNU_SOURCE                     /* syscall prototype */

+#include <stdbool.h>

 #include <stddef.h>

 #include <string.h>                     /* memset(), memcpy() */

 #include <assert.h>

@@ -89,6 +90,9 @@ typedef char ICHAR;

 /* Round up n to be a multiple of sz, where sz is a power of 2. */

 #define ROUND_UP(n, sz) (((n) + ((sz) - 1)) & ~((sz) - 1))

+/* Do safe (NULL-aware) pointer arithmetic */

+#define EXPAT_SAFE_PTR_DIFF(p, q) (((p) && (q)) ? ((p) - (q)) : 0)

+

 /* Handle the case where memmove() doesn't exist. */

 #ifndef HAVE_MEMMOVE

 #ifdef HAVE_BCOPY

@@ -98,6 +102,8 @@ typedef char ICHAR;

 #endif /* HAVE_BCOPY */

 #endif /* HAVE_MEMMOVE */

+#define EXPAT_MIN(a, b) (((a) < (b)) ? (a) : (b))

+

 #include "internal.h"

 #include "xmltok.h"

 #include "xmlrole.h"

@@ -476,6 +482,9 @@ parserInit(XML_Parser parser, const XML_

    ? 0 \

    : ((*((pool)->ptr)++ = c), 1))

+XML_Bool g_reparseDeferralEnabledDefault = XML_TRUE; // write ONLY in runtests.c

+unsigned int g_parseAttempts = 0;                    // used for testing only

+

 struct XML_ParserStruct {

   /* The first member must be userData so that the XML_GetUserData

      macro works. */

@@ -491,6 +500,9 @@ struct XML_ParserStruct {

   const char *m_bufferLim;

   XML_Index m_parseEndByteIndex;

   const char *m_parseEndPtr;

+  size_t m_partialTokenBytesBefore; /* used in heuristic to avoid O(n^2) */

+  XML_Bool m_reparseDeferralEnabled;

+  int m_lastBufferRequestSize;

   XML_Char *m_dataBuf;

   XML_Char *m_dataBufEnd;

   XML_StartElementHandler m_startElementHandler;

@@ -647,6 +659,9 @@ struct XML_ParserStruct {

 #define bufferEnd (parser->m_bufferEnd)

 #define parseEndByteIndex (parser->m_parseEndByteIndex)

 #define parseEndPtr (parser->m_parseEndPtr)

+#define partialTokenBytesBefore (parser->m_partialTokenBytesBefore)

+#define reparseDeferralEnabled (parser->m_reparseDeferralEnabled)

+#define lastBufferRequestSize (parser->m_lastBufferRequestSize)

 #define bufferLim (parser->m_bufferLim)

 #define dataBuf (parser->m_dataBuf)

 #define dataBufEnd (parser->m_dataBufEnd)

@@ -887,6 +902,47 @@ get_hash_secret_salt(XML_Parser parser)

   return parser->m_hash_secret_salt;

 }

+static enum XML_Error

+callProcessor(XML_Parser parser, const char *start, const char *end,

+              const char **endPtr) {

+  const size_t have_now = EXPAT_SAFE_PTR_DIFF(end, start);

+

+  if (parser->m_reparseDeferralEnabled

+      && ! parser->m_parsingStatus.finalBuffer) {

+    // Heuristic: don't try to parse a partial token again until the amount of

+    // available data has increased significantly.

+    const size_t had_before = parser->m_partialTokenBytesBefore;

+    // ...but *do* try anyway if we're close to causing a reallocation.

+    size_t available_buffer

+        = EXPAT_SAFE_PTR_DIFF(parser->m_bufferPtr, parser->m_buffer);

+#if XML_CONTEXT_BYTES > 0

+    available_buffer -= EXPAT_MIN(available_buffer, XML_CONTEXT_BYTES);

+#endif

+    available_buffer

+        += EXPAT_SAFE_PTR_DIFF(parser->m_bufferLim, parser->m_bufferEnd);

+    // m_lastBufferRequestSize is never assigned a value < 0, so the cast is ok

+    const bool enough

+        = (have_now >= 2 * had_before)

+          || ((size_t)parser->m_lastBufferRequestSize > available_buffer);

+

+    if (! enough) {

+      *endPtr = start; // callers may expect this to be set

+      return XML_ERROR_NONE;

+    }

+  }

+  g_parseAttempts += 1;

+  const enum XML_Error ret = parser->m_processor(parser, start, end, endPtr);

+  if (ret == XML_ERROR_NONE) {

+    // if we consumed nothing, remember what we had on this parse attempt.

+    if (*endPtr == start) {

+      parser->m_partialTokenBytesBefore = have_now;

+    } else {

+      parser->m_partialTokenBytesBefore = 0;

+    }

+  }

+  return ret;

+}

+

 static XML_Bool  /* only valid for root parser */

 startParsing(XML_Parser parser)

 {

@@ -1075,6 +1131,9 @@ parserInit(XML_Parser parser, const XML_

   bufferEnd = buffer;

   parseEndByteIndex = 0;

   parseEndPtr = NULL;

+  partialTokenBytesBefore = 0;

+  reparseDeferralEnabled = g_reparseDeferralEnabledDefault;

+  lastBufferRequestSize = 0;

   declElementType = NULL;

   declAttributeId = NULL;

   declEntity = NULL;

@@ -1232,6 +1291,7 @@ XML_ExternalEntityParserCreate(XML_Parse

      to worry which hash secrets each table has.

   */

   unsigned long oldhash_secret_salt;

+  XML_Bool oldReparseDeferralEnabled;

   /* Validate the oldParser parameter before we pull everything out of it */

   if (oldParser == NULL)

@@ -1276,6 +1336,7 @@ XML_ExternalEntityParserCreate(XML_Parse

      to worry which hash secrets each table has.

   */

   oldhash_secret_salt = hash_secret_salt;

+  oldReparseDeferralEnabled = reparseDeferralEnabled;

 #ifdef XML_DTD

   if (!context)

@@ -1330,6 +1391,7 @@ XML_ExternalEntityParserCreate(XML_Parse

   defaultExpandInternalEntities = oldDefaultExpandInternalEntities;

   ns_triplets = oldns_triplets;

   hash_secret_salt = oldhash_secret_salt;

+  reparseDeferralEnabled = oldReparseDeferralEnabled;

   parentParser = oldParser;

 #ifdef XML_DTD

   paramEntityParsing = oldParamEntityParsing;

@@ -1850,39 +1912,8 @@ XML_Parse(XML_Parser parser, const char

     ps_parsing = XML_PARSING;

   }

-  if (len == 0) {

-    ps_finalBuffer = (XML_Bool)isFinal;

-    if (!isFinal)

-      return XML_STATUS_OK;

-    positionPtr = bufferPtr;

-    parseEndPtr = bufferEnd;

-

-    /* If data are left over from last buffer, and we now know that these

-       data are the final chunk of input, then we have to check them again

-       to detect errors based on that fact.

-    */

-    errorCode = processor(parser, bufferPtr, parseEndPtr, &bufferPtr);

-

-    if (errorCode == XML_ERROR_NONE) {

-      switch (ps_parsing) {

-      case XML_SUSPENDED:

-        XmlUpdatePosition(encoding, positionPtr, bufferPtr, &position);

-        positionPtr = bufferPtr;

-        return XML_STATUS_SUSPENDED;

-      case XML_INITIALIZED:

-      case XML_PARSING:

-        ps_parsing = XML_FINISHED;

-        /* fall through */

-      default:

-        return XML_STATUS_OK;

-      }

-    }

-    eventEndPtr = eventPtr;

-    processor = errorProcessor;

-    return XML_STATUS_ERROR;

-  }

 #ifndef XML_CONTEXT_BYTES

-  else if (bufferPtr == bufferEnd) {

+  if (bufferPtr == bufferEnd) {

     const char *end;

     int nLeftOver;

     enum XML_Status result;

@@ -1899,11 +1930,14 @@ XML_Parse(XML_Parser parser, const char

        processor = errorProcessor;

        return XML_STATUS_ERROR;

     }

+    // though this isn't a buffer request, we assume that `len` is the app's

+    // preferred buffer fill size, and therefore save it here.

+    lastBufferRequestSize = len;

     parseEndByteIndex += len;

     positionPtr = s;

     ps_finalBuffer = (XML_Bool)isFinal;

-    errorCode = processor(parser, s, parseEndPtr = s + len, &end;;

+    errorCode = callProcessor(parser, s, parseEndPtr = s + len, &end;;

     if (errorCode != XML_ERROR_NONE) {

       eventEndPtr = eventPtr;

@@ -1930,6 +1964,8 @@ XML_Parse(XML_Parser parser, const char

     XmlUpdatePosition(encoding, positionPtr, end, &position);

     nLeftOver = s + len - end;

     if (nLeftOver) {

+#if 0

+// erAck: replace with XML_GetBuffer() below.

       if (buffer == NULL || nLeftOver > bufferLim - buffer) {

         /* avoid _signed_ integer overflow */

         char *temp = NULL;

@@ -1939,6 +1975,28 @@ XML_Parse(XML_Parser parser, const char

                 ? (char *)MALLOC(bytesToAllocate)

                 : (char *)REALLOC(buffer, bytesToAllocate));

         }

+#endif

+#if 1

+// erAck: the original patch context had a call to XML_GetBuffer() instead:

+      // Back up and restore the parsing status to avoid XML_ERROR_SUSPENDED

+      // (and XML_ERROR_FINISHED) from XML_GetBuffer.

+      const enum XML_Parsing originalStatus = ps_parsing;

+      ps_parsing = XML_PARSING;

+      void *const temp = XML_GetBuffer(parser, nLeftOver);

+      ps_parsing = originalStatus;

+#endif

+      // GetBuffer may have overwritten this, but we want to remember what the

+      // app requested, not how many bytes were left over after parsing.

+      lastBufferRequestSize = len;

+#if 1

+      if (temp == NULL) {

+        // NOTE: parser->m_errorCode has already been set by XML_GetBuffer().

+        eventPtr = eventEndPtr = NULL;

+        processor = errorProcessor;

+        return XML_STATUS_ERROR;

+      }

+#endif

+#if 0

         if (temp == NULL) {

           errorCode = XML_ERROR_NO_MEMORY;

           eventPtr = eventEndPtr = NULL;

@@ -1948,6 +2006,7 @@ XML_Parse(XML_Parser parser, const char

         buffer = temp;

         bufferLim = buffer + bytesToAllocate;

       }

+#endif

       memcpy(buffer, end, nLeftOver);

     }

     bufferPtr = buffer;

@@ -1959,15 +2018,14 @@ XML_Parse(XML_Parser parser, const char

     return result;

   }

 #endif  /* not defined XML_CONTEXT_BYTES */

-  else {

-    void *buff = XML_GetBuffer(parser, len);

-    if (buff == NULL)

-      return XML_STATUS_ERROR;

-    else {

-      memcpy(buff, s, len);

-      return XML_ParseBuffer(parser, len, isFinal);

-    }

+  void *buff = XML_GetBuffer(parser, len);

+  if (buff == NULL)

+    return XML_STATUS_ERROR;

+  if (len > 0) {

+    assert(s != NULL); // make sure s==NULL && len!=0 was rejected above

+    memcpy(buff, s, len);

   }

+  return XML_ParseBuffer(parser, len, isFinal);

 }

 enum XML_Status XMLCALL

@@ -2001,7 +2059,7 @@ XML_ParseBuffer(XML_Parser parser, int l

   parseEndByteIndex += len;

   ps_finalBuffer = (XML_Bool)isFinal;

-  errorCode = processor(parser, start, parseEndPtr, &bufferPtr);

+  errorCode = callProcessor(parser, start, parseEndPtr, &bufferPtr);

   if (errorCode != XML_ERROR_NONE) {

     eventEndPtr = eventPtr;

@@ -2047,7 +2105,11 @@ XML_GetBuffer(XML_Parser parser, int len

   default: ;

   }

-  if (len > bufferLim - bufferEnd) {

+  // whether or not the request succeeds, `len` seems to be the app's preferred

+  // buffer fill size; remember it.

+  lastBufferRequestSize = len;

+  if (len > EXPAT_SAFE_PTR_DIFF(bufferLim, bufferEnd)

+      || buffer == NULL) {

 #ifdef XML_CONTEXT_BYTES

     int keep;

 #endif  /* defined XML_CONTEXT_BYTES */

@@ -2063,7 +2125,9 @@ XML_GetBuffer(XML_Parser parser, int len

       keep = XML_CONTEXT_BYTES;

     neededSize += keep;

 #endif  /* defined XML_CONTEXT_BYTES */

-    if (neededSize  <= bufferLim - buffer) {

+    if (buffer && bufferPtr

+        && neededSize

+               <= EXPAT_SAFE_PTR_DIFF(bufferLim, buffer)) {

 #ifdef XML_CONTEXT_BYTES

       if (keep < bufferPtr - buffer) {

         int offset = (int)(bufferPtr - buffer) - keep;

@@ -2072,8 +2136,11 @@ XML_GetBuffer(XML_Parser parser, int len

         bufferPtr -= offset;

       }

 #else

-      memmove(buffer, bufferPtr, bufferEnd - bufferPtr);

-      bufferEnd = buffer + (bufferEnd - bufferPtr);

+      memmove(buffer, bufferPtr,

+              EXPAT_SAFE_PTR_DIFF(bufferEnd, bufferPtr));

+      bufferEnd

+          = buffer

+            + EXPAT_SAFE_PTR_DIFF(bufferEnd, bufferPtr);

       bufferPtr = buffer;

 #endif  /* not defined XML_CONTEXT_BYTES */

     }

@@ -2171,7 +2238,7 @@ XML_ResumeParser(XML_Parser parser)

   }

   ps_parsing = XML_PARSING;

-  errorCode = processor(parser, bufferPtr, parseEndPtr, &bufferPtr);

+  errorCode = callProcessor(parser, bufferPtr, parseEndPtr, &bufferPtr);

   if (errorCode != XML_ERROR_NONE) {

     eventEndPtr = eventPtr;

@@ -2481,6 +2548,15 @@ MOZ_XML_ProcessingEntityValue(XML_Parser

 }

 /* END MOZILLA CHANGE */

+XML_Bool XMLCALL

+XML_SetReparseDeferralEnabled(XML_Parser parser, XML_Bool enabled) {

+  if (parser != NULL && (enabled == XML_TRUE || enabled == XML_FALSE)) {

+    parser->m_reparseDeferralEnabled = enabled;

+    return XML_TRUE;

+  }

+  return XML_FALSE;

+}

+

 /* Initially tag->rawName always points into the parse buffer;

    for those TAG instances opened while the current parse buffer was

    processed, and not yet closed, we need to store tag->rawName in a more