[PATCH v3 08/10] shell32/autocomplete: Avoid another buffer overflow and handle arbitrary sizes for the auto-append string

[Gabriel Ivăncescu]

The previous code caps the auto-append text at 255 characters, which can be
easily exploited. It's also less efficient as it scans the string multiple
times.

Signed-off-by: Gabriel Ivăncescu 
---
 dlls/shell32/autocomplete.c | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/dlls/shell32/autocomplete.c b/dlls/shell32/autocomplete.c
index c46b897..fc4c595 100644
--- a/dlls/shell32/autocomplete.c
+++ b/dlls/shell32/autocomplete.c
@@ -286,12 +286,23 @@ static LRESULT APIENTRY ACEditSubclassProc(HWND hwnd, UINT uMsg, WPARAM wParam,

if (!strncmpiW(hwndText, strs, len)) {
                     if (cpt == 0 && noautoappend == FALSE) {
-                        WCHAR buffW[255];
+                        /* The character capitalization can be different,
+                           so merge hwndText and strs into a new string */
+                        WCHAR *tmp;
+                        size_t strslen = len + strlenW(&strs[len]);
+
+                        if ((tmp = heap_alloc((strslen+1) * sizeof(WCHAR))))
+                        {
+                            memcpy(tmp, hwndText, len * sizeof(WCHAR));
+                            memcpy(&tmp[len], &strs[len], (strslen-len+1) * sizeof(WCHAR));
+                        }
+                        else tmp = strs;
+
+                        SendMessageW(hwnd, WM_SETTEXT, 0, (LPARAM)tmp);
+                        SendMessageW(hwnd, EM_SETSEL, len, strslen);
+                        if (tmp != strs)
+                            heap_free(tmp);

-                        strcpyW(buffW, hwndText);
-                        strcatW(buffW, &strs[len]);
-                        SetWindowTextW(hwnd, buffW);
-                        SendMessageW(hwnd, EM_SETSEL, len, strlenW(strs));
                         if (!(This->options & ACO_AUTOSUGGEST)) {
                             CoTaskMemFree(strs);
                             break;