TobbeSweden
26th January 2009 09:53 UTC

Crash when getting user's groups
Why does the following code crash sometimes when I run it?

Name "EnumUsersGroups"
OutFile "EnumUsersGroups.exe"

!macro GetUserGroups SERVER_NAME USERNAME GROUP_ARRAY_NAME
    Push $R0
    Push $R1
    Push $R2
    Push $R3

    # NET_API_STATUS NetUserGetLocalGroups(
    #     __in   LPCWSTR servername,
    #     __in   LPCWSTR username,
    #     __in   DWORD level,
    #     __in   DWORD flags,
    #     __out  LPBYTE *bufptr,
    #     __in   DWORD prefmaxlen,
    #     __out  LPDWORD entriesread,
    #     __out  LPDWORD totalentries
    # );

    # $R0 buffer with an array of LOCALGROUP_USERS_INFO_0 structures
    # $R1 holds the number of entries processed
    System::Call 'netapi32::NetUserGetLocalGroups(w "${SERVER_NAME}", w "${USERNAME}", \
        i 0, i 0, *i .R0, i ${NSIS_MAX_STRLEN}, *i .R1, *i .R2) i .R3'
    StrCpy $R2 $R0 ; Needed to free the buffer later

    # check for error
    StrCmp $R3 0 +1 +2

    System::Call "*$R0(w.R3)"

    # Cleanup
    StrCmp $R2 0 +2
        System::Call 'netapi32.dll::NetApiBufferFree(i R2) i .R0'

    Pop $R3
    Pop $R2
    Pop $R1
    Pop $R0
!macroend

!define GetUserGroups "!insertmacro GetUserGroups"

ShowInstDetails show
Page instfiles

Section ""
    ${GetUserGroups} "" "Tobbe" GroupArray
SectionEnd

TobbeSweden
26th January 2009 10:10 UTC

I have trimmed the code down in the post above to show the minimal code that still crashes.

If I remove the line 'System::Call "*$R0(w.R3)"' the crash goes away.

What am I doing wrong?

Anders
26th January 2009 14:18 UTC

other than the fact that you are passing NSIS_MAX_STRLEN for some weird reason, I don't see anything wrong

this code works fine for me

!define USERNAME Anders
System::Call 'netapi32::NetUserGetLocalGroups(i 0, w "${USERNAME}",i 0, i 0, *i .R0, i -1, *i .R1, *i .R2)i.R3'
StrCpy $0 $R0
loop:
${If} $R1 > 0
        System::Call "*$0(w.r1)"
        DetailPrint "$R1: $1"
        IntOp $0 $0 + 4
        IntOp $R1 $R1 - 1
        goto loop
${EndIf}
System::Call 'netapi32.dll::NetApiBufferFree(i $R0)i.R0'

Also, don't forget that a user might have deny only groups in their token, so even if administrator is returned, your process might not have admin rights (use the userinfo plugin for this detection)

TobbeSweden
26th January 2009 14:34 UTC

The reason I had NSIS_MAX_STRLEN was because that's what the original macro had... http://nsis.sourceforge.net/User_Man...s_Group.28s.29

Using -1 instead stops it from crashing :D Thanks a lot!

Am I correct in assuming that -1 is the biggest possible value for that parameter?

Also, don't forget that a user might have deny only groups in their token

I don't understand this. Can you please explain more?

Anders
26th January 2009 22:14 UTC

-1 = MAX_PREFERRED_LENGTH

I don't know why you need this code, but you just need to know that even if NetUserGetLocalGroups returns with Administrator as a group, it does not mean that you can do admin stuff, it is not the correct way to check if the current process has admin rights

TobbeSweden
26th January 2009 23:11 UTC

Thanks.

I'm not using this to check if the current process has admin rights :)