[libxml2] [CVE-2022-29824] Fix integer overflows in xmlBuf and xmlBuffer

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 6c283d83eccd940bcde15634ac8c7f100e3caefd
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Tue Mar 8 20:10:02 2022 +0100

    [CVE-2022-29824] Fix integer overflows in xmlBuf and xmlBuffer
    
    In several places, the code handling string buffers didn't check for
    integer overflow or used wrong types for buffer sizes. This could
    result in out-of-bounds writes or other memory errors when working on
    large, multi-gigabyte buffers.
    
    Thanks to Felix Wilhelm for the report.

 buf.c  | 84 ++++++++++++++++++++++++++----------------------------------------
 tree.c | 72 +++++++++++++++++++++-----------------------------------
 2 files changed, 60 insertions(+), 96 deletions(-)
---
diff --git a/buf.c b/buf.c
index 9d95e801..2b1fd793 100644
--- a/buf.c
+++ b/buf.c
@@ -26,6 +26,10 @@
 #include <libxml/parserInternals.h> /* for XML_MAX_TEXT_LENGTH */
 #include "buf.h"
 
+#ifndef SIZE_MAX
+#define SIZE_MAX ((size_t) -1)
+#endif
+
 #define WITH_BUFFER_COMPAT
 
 /**
@@ -151,6 +155,8 @@ xmlBufPtr
 xmlBufCreateSize(size_t size) {
     xmlBufPtr ret;
 
+    if (size == SIZE_MAX)
+        return(NULL);
     ret = (xmlBufPtr) xmlMalloc(sizeof(xmlBuf));
     if (ret == NULL) {
        xmlBufMemoryError(NULL, "creating buffer");
@@ -160,7 +166,7 @@ xmlBufCreateSize(size_t size) {
     ret->error = 0;
     ret->buffer = NULL;
     ret->alloc = xmlBufferAllocScheme;
-    ret->size = (size ? size+2 : 0);         /* +1 for ending null */
+    ret->size = (size ? size + 1 : 0);         /* +1 for ending null */
     UPDATE_COMPAT(ret);
     if (ret->size){
         ret->content = (xmlChar *) xmlMallocAtomic(ret->size * sizeof(xmlChar));
@@ -429,23 +435,17 @@ xmlBufGrowInternal(xmlBufPtr buf, size_t len) {
     CHECK_COMPAT(buf)
 
     if (buf->alloc == XML_BUFFER_ALLOC_IMMUTABLE) return(0);
-    if (buf->use + len < buf->size)
+    if (len < buf->size - buf->use)
         return(buf->size - buf->use);
+    if (len > SIZE_MAX - buf->use)
+        return(0);
 
-    /*
-     * Windows has a BIG problem on realloc timing, so we try to double
-     * the buffer size (if that's enough) (bug 146697)
-     * Apparently BSD too, and it's probably best for linux too
-     * On an embedded system this may be something to change
-     */
-#if 1
-    if (buf->size > (size_t) len)
-        size = buf->size * 2;
-    else
-        size = buf->use + len + 100;
-#else
-    size = buf->use + len + 100;
-#endif
+    if (buf->size > (size_t) len) {
+        size = buf->size > SIZE_MAX / 2 ? SIZE_MAX : buf->size * 2;
+    } else {
+        size = buf->use + len;
+        size = size > SIZE_MAX - 100 ? SIZE_MAX : size + 100;
+    }
 
     if (buf->alloc == XML_BUFFER_ALLOC_BOUNDED) {
         /*
@@ -731,7 +731,7 @@ xmlBufIsEmpty(const xmlBufPtr buf)
 int
 xmlBufResize(xmlBufPtr buf, size_t size)
 {
-    unsigned int newSize;
+    size_t newSize;
     xmlChar* rebuf = NULL;
     size_t start_buf;
 
@@ -759,9 +759,13 @@ xmlBufResize(xmlBufPtr buf, size_t size)
        case XML_BUFFER_ALLOC_IO:
        case XML_BUFFER_ALLOC_DOUBLEIT:
            /*take care of empty case*/
-           newSize = (buf->size ? buf->size*2 : size + 10);
+            if (buf->size == 0) {
+                newSize = (size > SIZE_MAX - 10 ? SIZE_MAX : size + 10);
+            } else {
+                newSize = buf->size;
+            }
            while (size > newSize) {
-               if (newSize > UINT_MAX / 2) {
+               if (newSize > SIZE_MAX / 2) {
                    xmlBufMemoryError(buf, "growing buffer");
                    return 0;
                }
@@ -769,15 +773,15 @@ xmlBufResize(xmlBufPtr buf, size_t size)
            }
            break;
        case XML_BUFFER_ALLOC_EXACT:
-           newSize = size+10;
+            newSize = (size > SIZE_MAX - 10 ? SIZE_MAX : size + 10);
            break;
         case XML_BUFFER_ALLOC_HYBRID:
             if (buf->use < BASE_BUFFER_SIZE)
                 newSize = size;
             else {
-                newSize = buf->size * 2;
+                newSize = buf->size;
                 while (size > newSize) {
-                    if (newSize > UINT_MAX / 2) {
+                    if (newSize > SIZE_MAX / 2) {
                         xmlBufMemoryError(buf, "growing buffer");
                         return 0;
                     }
@@ -787,7 +791,7 @@ xmlBufResize(xmlBufPtr buf, size_t size)
             break;
 
        default:
-           newSize = size+10;
+            newSize = (size > SIZE_MAX - 10 ? SIZE_MAX : size + 10);
            break;
     }
 
@@ -853,7 +857,7 @@ xmlBufResize(xmlBufPtr buf, size_t size)
  */
 int
 xmlBufAdd(xmlBufPtr buf, const xmlChar *str, int len) {
-    unsigned int needSize;
+    size_t needSize;
 
     if ((str == NULL) || (buf == NULL) || (buf->error))
        return -1;
@@ -875,8 +879,10 @@ xmlBufAdd(xmlBufPtr buf, const xmlChar *str, int len) {
     if (len < 0) return -1;
     if (len == 0) return 0;
 
-    needSize = buf->use + len + 2;
-    if (needSize > buf->size){
+    if ((size_t) len >= buf->size - buf->use) {
+        if ((size_t) len >= SIZE_MAX - buf->use)
+            return(-1);
+        needSize = buf->use + len + 1;
        if (buf->alloc == XML_BUFFER_ALLOC_BOUNDED) {
            /*
             * Used to provide parsing limits
@@ -1012,31 +1018,7 @@ xmlBufCat(xmlBufPtr buf, const xmlChar *str) {
  */
 int
 xmlBufCCat(xmlBufPtr buf, const char *str) {
-    const char *cur;
-
-    if ((buf == NULL) || (buf->error))
-        return(-1);
-    CHECK_COMPAT(buf)
-    if (buf->alloc == XML_BUFFER_ALLOC_IMMUTABLE) return -1;
-    if (str == NULL) {
-#ifdef DEBUG_BUFFER
-        xmlGenericError(xmlGenericErrorContext,
-               "xmlBufCCat: str == NULL\n");
-#endif
-       return -1;
-    }
-    for (cur = str;*cur != 0;cur++) {
-        if (buf->use  + 10 >= buf->size) {
-            if (!xmlBufResize(buf, buf->use+10)){
-               xmlBufMemoryError(buf, "growing buffer");
-                return XML_ERR_NO_MEMORY;
-            }
-        }
-        buf->content[buf->use++] = *cur;
-    }
-    buf->content[buf->use] = 0;
-    UPDATE_COMPAT(buf)
-    return 0;
+    return xmlBufCat(buf, (const xmlChar *) str);
 }
 
 /**
diff --git a/tree.c b/tree.c
index 2b02df3d..689a6b66 100644
--- a/tree.c
+++ b/tree.c
@@ -7120,6 +7120,8 @@ xmlBufferPtr
 xmlBufferCreateSize(size_t size) {
     xmlBufferPtr ret;
 
+    if (size >= UINT_MAX)
+        return(NULL);
     ret = (xmlBufferPtr) xmlMalloc(sizeof(xmlBuffer));
     if (ret == NULL) {
        xmlTreeErrMemory("creating buffer");
@@ -7127,7 +7129,7 @@ xmlBufferCreateSize(size_t size) {
     }
     ret->use = 0;
     ret->alloc = xmlBufferAllocScheme;
-    ret->size = (size ? size+2 : 0);         /* +1 for ending null */
+    ret->size = (size ? size + 1 : 0);         /* +1 for ending null */
     if (ret->size){
         ret->content = (xmlChar *) xmlMallocAtomic(ret->size * sizeof(xmlChar));
         if (ret->content == NULL) {
@@ -7187,6 +7189,8 @@ xmlBufferCreateStatic(void *mem, size_t size) {
 
     if ((mem == NULL) || (size == 0))
         return(NULL);
+    if (size > UINT_MAX)
+        return(NULL);
 
     ret = (xmlBufferPtr) xmlMalloc(sizeof(xmlBuffer));
     if (ret == NULL) {
@@ -7334,28 +7338,23 @@ xmlBufferShrink(xmlBufferPtr buf, unsigned int len) {
  */
 int
 xmlBufferGrow(xmlBufferPtr buf, unsigned int len) {
-    int size;
+    unsigned int size;
     xmlChar *newbuf;
 
     if (buf == NULL) return(-1);
 
     if (buf->alloc == XML_BUFFER_ALLOC_IMMUTABLE) return(0);
-    if (len + buf->use < buf->size) return(0);
+    if (len < buf->size - buf->use)
+        return(0);
+    if (len > UINT_MAX - buf->use)
+        return(-1);
 
-    /*
-     * Windows has a BIG problem on realloc timing, so we try to double
-     * the buffer size (if that's enough) (bug 146697)
-     * Apparently BSD too, and it's probably best for linux too
-     * On an embedded system this may be something to change
-     */
-#if 1
-    if (buf->size > len)
-        size = buf->size * 2;
-    else
-        size = buf->use + len + 100;
-#else
-    size = buf->use + len + 100;
-#endif
+    if (buf->size > (size_t) len) {
+        size = buf->size > UINT_MAX / 2 ? UINT_MAX : buf->size * 2;
+    } else {
+        size = buf->use + len;
+        size = size > UINT_MAX - 100 ? UINT_MAX : size + 100;
+    }
 
     if ((buf->alloc == XML_BUFFER_ALLOC_IO) && (buf->contentIO != NULL)) {
         size_t start_buf = buf->content - buf->contentIO;
@@ -7482,7 +7481,10 @@ xmlBufferResize(xmlBufferPtr buf, unsigned int size)
        case XML_BUFFER_ALLOC_IO:
        case XML_BUFFER_ALLOC_DOUBLEIT:
            /*take care of empty case*/
-           newSize = (buf->size ? buf->size : size + 10);
+            if (buf->size == 0)
+                newSize = (size > UINT_MAX - 10 ? UINT_MAX : size + 10);
+            else
+                newSize = buf->size;
            while (size > newSize) {
                if (newSize > UINT_MAX / 2) {
                    xmlTreeErrMemory("growing buffer");
@@ -7492,7 +7494,7 @@ xmlBufferResize(xmlBufferPtr buf, unsigned int size)
            }
            break;
        case XML_BUFFER_ALLOC_EXACT:
-           newSize = size+10;
+           newSize = (size > UINT_MAX - 10 ? UINT_MAX : size + 10);;
            break;
         case XML_BUFFER_ALLOC_HYBRID:
             if (buf->use < BASE_BUFFER_SIZE)
@@ -7510,7 +7512,7 @@ xmlBufferResize(xmlBufferPtr buf, unsigned int size)
             break;
 
        default:
-           newSize = size+10;
+           newSize = (size > UINT_MAX - 10 ? UINT_MAX : size + 10);;
            break;
     }
 
@@ -7596,8 +7598,10 @@ xmlBufferAdd(xmlBufferPtr buf, const xmlChar *str, int len) {
     if (len < 0) return -1;
     if (len == 0) return 0;
 
-    needSize = buf->use + len + 2;
-    if (needSize > buf->size){
+    if ((unsigned) len >= buf->size - buf->use) {
+        if ((unsigned) len >= UINT_MAX - buf->use)
+            return XML_ERR_NO_MEMORY;
+        needSize = buf->use + len + 1;
         if (!xmlBufferResize(buf, needSize)){
            xmlTreeErrMemory("growing buffer");
             return XML_ERR_NO_MEMORY;
@@ -7710,29 +7714,7 @@ xmlBufferCat(xmlBufferPtr buf, const xmlChar *str) {
  */
 int
 xmlBufferCCat(xmlBufferPtr buf, const char *str) {
-    const char *cur;
-
-    if (buf == NULL)
-        return(-1);
-    if (buf->alloc == XML_BUFFER_ALLOC_IMMUTABLE) return -1;
-    if (str == NULL) {
-#ifdef DEBUG_BUFFER
-        xmlGenericError(xmlGenericErrorContext,
-               "xmlBufferCCat: str == NULL\n");
-#endif
-       return -1;
-    }
-    for (cur = str;*cur != 0;cur++) {
-        if (buf->use  + 10 >= buf->size) {
-            if (!xmlBufferResize(buf, buf->use+10)){
-               xmlTreeErrMemory("growing buffer");
-                return XML_ERR_NO_MEMORY;
-            }
-        }
-        buf->content[buf->use++] = *cur;
-    }
-    buf->content[buf->use] = 0;
-    return 0;
+    return xmlBufferCat(buf, (const xmlChar *) str);
 }
 
 /**