[libxml2/ddkilzer/fix-missing-xmlBuf-xmlBuffer-NUL-terminators] Fix missing NUL terminators in xmlBuf and xmlBuffer functions

[David Kilzer <ddkilzer src gnome org>]

commit 78a4920847b4354bdb1cad999340200b6ee26a2b
Author: David Kilzer <ddkilzer apple com>
Date:   Sun May 29 09:46:00 2022 -0700

    Fix missing NUL terminators in xmlBuf and xmlBuffer functions
    
    * buf.c:
    (xmlBufGrowInternal):
    - Always set NUL terminator at the end of the current buffer.
      Code paths that resized the buffer failed to set the NUL
      termintor.
    (xmlBufAddLen):
    - Change check for remaining space to account for the NUL
      terminator.  When adding a length exactly equal to the number
      of unused bytes, a NUL terminator was not written.
    (xmlBufResize):
    - Move setting of NUL terminator to common code.  More than one
      path through the function failed to set a NUL terminator.
    * tree.c:
    (xmlBufferGrow):
    - Always set NUL terminator at the end of the current buffer.
      Resizing the buffer failed to set the NUL termintor.
    (xmlBufferResize):
    - Move setting of NUL terminator to common code.  More than one
      path through the function failed to set a NUL terminator.
    (xmlBufferAddHead):
    - Set NUL terminator before returning early when shifting
      contents.

 buf.c  | 11 ++++-------
 tree.c |  5 +++--
 2 files changed, 7 insertions(+), 9 deletions(-)
---
diff --git a/buf.c b/buf.c
index 0a798f59..b9bc2f30 100644
--- a/buf.c
+++ b/buf.c
@@ -478,6 +478,7 @@ xmlBufGrowInternal(xmlBufPtr buf, size_t len) {
        buf->content = newbuf;
     }
     buf->size = size;
+    buf->content[buf->use] = 0;
     UPDATE_COMPAT(buf)
     return(buf->size - buf->use);
 }
@@ -591,14 +592,11 @@ xmlBufAddLen(xmlBufPtr buf, size_t len) {
     if ((buf == NULL) || (buf->error))
         return(-1);
     CHECK_COMPAT(buf)
-    if (len > (buf->size - buf->use))
+    if (len >= (buf->size - buf->use))
         return(-1);
     buf->use += len;
+    buf->content[buf->use] = 0;
     UPDATE_COMPAT(buf)
-    if (buf->size > buf->use)
-        buf->content[buf->use] = 0;
-    else
-        return(-1);
     return(0);
 }
 
@@ -762,7 +760,6 @@ xmlBufResize(xmlBufPtr buf, size_t size)
            /* move data back to start */
            memmove(buf->contentIO, buf->content, buf->use);
            buf->content = buf->contentIO;
-           buf->content[buf->use] = 0;
            buf->size += start_buf;
        } else {
            rebuf = (xmlChar *) xmlRealloc(buf->contentIO, start_buf + newSize);
@@ -788,7 +785,6 @@ xmlBufResize(xmlBufPtr buf, size_t size)
            if (rebuf != NULL) {
                memcpy(rebuf, buf->content, buf->use);
                xmlFree(buf->content);
-               rebuf[buf->use] = 0;
            }
        }
        if (rebuf == NULL) {
@@ -798,6 +794,7 @@ xmlBufResize(xmlBufPtr buf, size_t size)
        buf->content = rebuf;
     }
     buf->size = newSize;
+    buf->content[buf->use] = 0;
     UPDATE_COMPAT(buf)
 
     return 1;
diff --git a/tree.c b/tree.c
index df17fa33..b5d94c57 100644
--- a/tree.c
+++ b/tree.c
@@ -7400,6 +7400,7 @@ xmlBufferGrow(xmlBufferPtr buf, unsigned int len) {
        buf->content = newbuf;
     }
     buf->size = size;
+    buf->content[buf->use] = 0;
     return(buf->size - buf->use);
 }
 
@@ -7548,7 +7549,6 @@ xmlBufferResize(xmlBufferPtr buf, unsigned int size)
            /* move data back to start */
            memmove(buf->contentIO, buf->content, buf->use);
            buf->content = buf->contentIO;
-           buf->content[buf->use] = 0;
            buf->size += start_buf;
        } else {
            rebuf = (xmlChar *) xmlRealloc(buf->contentIO, start_buf + newSize);
@@ -7574,7 +7574,6 @@ xmlBufferResize(xmlBufferPtr buf, unsigned int size)
            if (rebuf != NULL) {
                memcpy(rebuf, buf->content, buf->use);
                xmlFree(buf->content);
-               rebuf[buf->use] = 0;
            }
        }
        if (rebuf == NULL) {
@@ -7584,6 +7583,7 @@ xmlBufferResize(xmlBufferPtr buf, unsigned int size)
        buf->content = rebuf;
     }
     buf->size = newSize;
+    buf->content[buf->use] = 0;
 
     return 1;
 }
@@ -7690,6 +7690,7 @@ xmlBufferAddHead(xmlBufferPtr buf, const xmlChar *str, int len) {
             memmove(&buf->content[0], str, len);
            buf->use += len;
            buf->size += len;
+            buf->content[buf->use] = 0;
            return(0);
        }
     }