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

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?

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)

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 😁 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?

-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

Thanks.

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