[PULL 2/5] qga/win32: Use rundll for VSS installation

[Konstantin Kostiuk]

The custom action uses cmd.exe to run VSS Service installation
and removal which causes an interactive command shell to spawn.
This shell can be used to execute any commands as a SYSTEM user.
Even if call qemu-ga.exe directly the interactive command shell
will be spawned as qemu-ga.exe is a console application and used
by users from the console as well as a service.

As VSS Service runs from DLL which contains the installer and
uninstaller code, it can be run directly by rundll32.exe without
any interactive command shell.

Add specific entry points for rundll which is just a wrapper
for COMRegister/COMUnregister functions with proper arguments.

resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2167423
fixes: CVE-2023-0664 (part 2 of 2)

Signed-off-by: Konstantin Kostiuk <kkostiuk@redhat.com>
Reviewed-by: Yan Vugenfirer <yvugenfi@redhat.com>
Reported-by: Brian Wiltse <brian.wiltse@live.com>
---
 qga/installer/qemu-ga.wxs | 10 +++++-----
 qga/vss-win32/install.cpp |  9 +++++++++
 qga/vss-win32/qga-vss.def |  2 ++
 3 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/qga/installer/qemu-ga.wxs b/qga/installer/qemu-ga.wxs
index feb629ec47..46ae9e7a13 100644
--- a/qga/installer/qemu-ga.wxs
+++ b/qga/installer/qemu-ga.wxs
@@ -127,22 +127,22 @@
       </Directory>
     </Directory>
 
-    <Property Id="cmd" Value="cmd.exe"/>
+    <Property Id="rundll" Value="rundll32.exe"/>
     <Property Id="REINSTALLMODE" Value="amus"/>
 
     <?ifdef var.InstallVss?>
     <CustomAction Id="RegisterCom"
-              ExeCommand='/c "[qemu_ga_directory]qemu-ga.exe" -s vss-install'
+              ExeCommand='"[qemu_ga_directory]qga-vss.dll",DLLCOMRegister'
               Execute="deferred"
-              Property="cmd"
+              Property="rundll"
               Impersonate="no"
               Return="check"
               >
     </CustomAction>
     <CustomAction Id="UnRegisterCom"
-              ExeCommand='/c "[qemu_ga_directory]qemu-ga.exe" -s vss-uninstall'
+              ExeCommand='"[qemu_ga_directory]qga-vss.dll",DLLCOMUnregister'
               Execute="deferred"
-              Property="cmd"
+              Property="rundll"
               Impersonate="no"
               Return="check"
               >
diff --git a/qga/vss-win32/install.cpp b/qga/vss-win32/install.cpp
index b57508fbe0..68662a6dfc 100644
--- a/qga/vss-win32/install.cpp
+++ b/qga/vss-win32/install.cpp
@@ -357,6 +357,15 @@ out:
     return hr;
 }
 
+STDAPI_(void) CALLBACK DLLCOMRegister(HWND, HINSTANCE, LPSTR, int)
+{
+    COMRegister();
+}
+
+STDAPI_(void) CALLBACK DLLCOMUnregister(HWND, HINSTANCE, LPSTR, int)
+{
+    COMUnregister();
+}
 
 static BOOL CreateRegistryKey(LPCTSTR key, LPCTSTR value, LPCTSTR data)
 {
diff --git a/qga/vss-win32/qga-vss.def b/qga/vss-win32/qga-vss.def
index 927782c31b..ee97a81427 100644
--- a/qga/vss-win32/qga-vss.def
+++ b/qga/vss-win32/qga-vss.def
@@ -1,6 +1,8 @@
 LIBRARY      "QGA-PROVIDER.DLL"
 
 EXPORTS
+       DLLCOMRegister
+       DLLCOMUnregister
        COMRegister             PRIVATE
        COMUnregister           PRIVATE
        DllCanUnloadNow         PRIVATE
-- 
2.25.1