Remove support for out of bounds params in Delete

The existing implementation of Delete on the string classes handles
some cases where the range being deleted is out of bounds by clipping
it to the valid range. This behaviour can lead to programming problems
in the calling code being masked by the fact the Delete method still
does something. The new version of these methods does an early return
if the parameters are invalid.

This change also effectively removes support for negative string sizes
from the Delete method, so converting FX_STRSIZE to be unsigned will
be easier.

BUG=pdfium:828

Change-Id: Idbb4a62f70a75eba06e7809e011b25da2d7404c4
Reviewed-on: https://pdfium-review.googlesource.com/9890
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Ryan Harrison <rharrison@chromium.org>

1 files changed, 13 insertions, 16 deletions

diff --git a/core/fxcrt/cfx_bytestring.cpp b/core/fxcrt/cfx_bytestring.cpp
index e031c87d2d..6cbd15e693 100644
--- a/core/fxcrt/cfx_bytestring.cpp
+++ b/core/fxcrt/cfx_bytestring.cpp
@@ -411,26 +411,23 @@ char* CFX_ByteString::GetBuffer(FX_STRSIZE nMinBufLength) {
   return m_pData->m_String;
 }
 
-FX_STRSIZE CFX_ByteString::Delete(FX_STRSIZE nIndex, FX_STRSIZE nCount) {
+FX_STRSIZE CFX_ByteString::Delete(FX_STRSIZE index, FX_STRSIZE count) {
   if (!m_pData)
     return 0;
 
-  if (nIndex < 0)
-    nIndex = 0;
+  FX_STRSIZE old_length = m_pData->m_nDataLength;
+  if (count <= 0 || index != pdfium::clamp(index, 0, old_length))
+    return old_length;
 
-  FX_STRSIZE nOldLength = m_pData->m_nDataLength;
-  if (nCount > 0 && nIndex < nOldLength) {
-    FX_STRSIZE mLength = nIndex + nCount;
-    if (mLength >= nOldLength) {
-      m_pData->m_nDataLength = nIndex;
-      return m_pData->m_nDataLength;
-    }
-    ReallocBeforeWrite(nOldLength);
-    int nCharsToCopy = nOldLength - mLength + 1;
-    memmove(m_pData->m_String + nIndex, m_pData->m_String + mLength,
-            nCharsToCopy);
-    m_pData->m_nDataLength = nOldLength - nCount;
-  }
+  FX_STRSIZE removal_length = index + count;
+  if (removal_length > old_length)
+    return old_length;
+
+  ReallocBeforeWrite(old_length);
+  int chars_to_copy = old_length - removal_length + 1;
+  memmove(m_pData->m_String + index, m_pData->m_String + removal_length,
+          chars_to_copy);
+  m_pData->m_nDataLength = old_length - count;
   return m_pData->m_nDataLength;
 }