path: root/expat-CVE-2023-52425.patch

# 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