[Bug 20336] New: GetDriveTypeW exposes partially uninitialized out parameter iosb in NtDeviceIoControlFile ?

http://bugs.winehq.org/show_bug.cgi?id=20336

Summary: GetDriveTypeW exposes partially uninitialized out
                    parameter iosb in NtDeviceIoControlFile ?
           Product: Wine
           Version: 1.1.31
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Keywords: download, patch
          Severity: normal
          Priority: P2
         Component: ntdll
        AssignedTo: [e-mail]
        ReportedBy: [e-mail]

Building the chromium unit test suite and then running

valgrind --trace-children=all --track-origins=yes wine base_unittests.exe
--gtest_filter=FileUtilTest.CreateShortcutTest

sometimes yields the error

Syscall param writev(vector[...]) points to uninitialised byte(s)
   at writev (writev.c:46)
   by wine_server_call (server.c:214)
   by NTDLL_wait_for_multiple_objects (sync.c:1122)
   by NtWaitForMultipleObjects (sync.c:1166)
   by NtWaitForSingleObject (sync.c:1175)
   by server_ioctl_file (file.c:1252)
   by NtDeviceIoControlFile (file.c:1318)
   by DeviceIoControl (file.c:2379)
   by get_mountmgr_drive_type (volume.c:203)
   by GetDriveTypeW (volume.c:1381)
   by IShellLinkW_fnSetPath (shelllink.c:2155)
   ...
 Address 0x7f21f248 is on thread 1's stack
 Uninitialised value was created by a stack allocation
   at DeviceIoControl (file.c:2335)

and sometimes the error

Syscall param writev(vector[...]) points to uninitialised byte(s)
   at writev (writev.c:46)
   by wine_server_call (server.c:214)
   by NTDLL_wait_for_multiple_objects (sync.c:1122)
   by wait_suspend (exception.c:85)
   by usr1_handler (signal_i386.c:1993)
   by ??? (in /lib32/libpthread-2.9.so)
 Address 0x7ffdae08 is on thread 1's stack 
 Uninitialised value was created by a stack allocation
   at DeviceIoControl (file.c:2335)

The stack allocation in question is 
        IO_STATUS_BLOCK iosb;
in kernel32/file.c in DeviceIoControl().  Setting its fields
to known values before the call to NtDeviceIoControlFile()
shows that the undefined field is iosb.Information.
Setting that field before the call gets rid of the valgrind error.

I can't quite follow how ioctl's work, but:
the IOCTL_MOUNTMGR_QUERY_UNIX_DRIVE ioctl seems
to follow the call-once-to-get-buffer-size paradigm.
Its reply is a struct mountmgr_unix_drive plus
(if there is room) two nul-terminated strings.
The first field of that struct is the total size needed
to hold the entire reply.  If you call without a
big enough buffer, it fills in the size and returns
STATUS_MORE_ENTRIES.  It puts 0 in the Information field
of the iosb in this case.
GetDriveTypeW happens to not care about the two strings,
so it only calls once with a small buffer.

Now, server_ioctl_file only copies the Information field 
of the iosb if it gets STATUS_SUCCESS.  So it leaves
Information undefined in the STATUS_MORE_ENTRIES case.
MSDN says that Information is set to zero on failure,
so if server_ioctl_file isn't going to copy that field,
maybe it should set it to zero.  And in fact, setting
it to zero in the non-STATUS_SUCCESS case also gets
rid of the valgrind error.

I have no idea what Information is used for, or what's
really going on here, so I'll just attach the patch
to clear Information in the non-SUCCESS case and
hope somebody who knows what's going on can comment.