[libxml2] Fix integer overflow in xmlBufferResize

[Nick Wellnhofer <nwellnhof src gnome org>]

commit b07251215ef48c70c6e56f7351406c47cfca4d5b
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Fri Jan 10 15:55:07 2020 +0100

    Fix integer overflow in xmlBufferResize
    
    Found by OSS-Fuzz.

 tree.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)
---
diff --git a/tree.c b/tree.c
index 0d7fc98c..f43f6de1 100644
--- a/tree.c
+++ b/tree.c
@@ -7424,12 +7424,17 @@ xmlBufferResize(xmlBufferPtr buf, unsigned int size)
     if (size < buf->size)
         return 1;
 
+    if (size > UINT_MAX - 10) {
+        xmlTreeErrMemory("growing buffer");
+        return 0;
+    }
+
     /* figure out new size */
     switch (buf->alloc){
        case XML_BUFFER_ALLOC_IO:
        case XML_BUFFER_ALLOC_DOUBLEIT:
            /*take care of empty case*/
-           newSize = (buf->size ? buf->size*2 : size + 10);
+           newSize = (buf->size ? buf->size : size + 10);
            while (size > newSize) {
                if (newSize > UINT_MAX / 2) {
                    xmlTreeErrMemory("growing buffer");
@@ -7445,7 +7450,7 @@ xmlBufferResize(xmlBufferPtr buf, unsigned int size)
             if (buf->use < BASE_BUFFER_SIZE)
                 newSize = size;
             else {
-                newSize = buf->size * 2;
+                newSize = buf->size;
                 while (size > newSize) {
                     if (newSize > UINT_MAX / 2) {
                         xmlTreeErrMemory("growing buffer");