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From:	"A. Wik (awik32 AT gmail DOT com) [via djgpp AT delorie DOT com]" <djgpp AT delorie DOT com>
Date:	Fri, 24 Jul 2020 13:28:36 +0000
Message-ID:	<CALPW7mS5nMXUwsyU2mhi-AXkhG4VCrqUB5bqgN9=p-RLabbjtw@mail.gmail.com>
Subject:	Re: User id
To:	djgpp AT delorie DOT com
Reply-To:	djgpp AT delorie DOT com

Hi,

and thanks for your elaborate reply.

On Thu, 23 Jul 2020 at 19:15, Juan Manuel Guerrero
(juan DOT guerrero AT gmx DOT de) [via djgpp AT delorie DOT com] <djgpp AT delorie DOT com>
wrote:
>
> Am 21.07.2020 21:25, schrieb A. Wik (awik32 AT gmail DOT com) [via djgpp AT delorie DOT com]:
> > Hi all,
> >
> > How do I convince BASH that I'm root and that my UID is 0 and not 42?
> >
> > I've tried editing the "djgpp.env" file.
> >
> > I also tried installing an "etc/passwd" file under the djgpp
> > directory, with "dosuser" listed as having uid 0.
> >
> > Regards,
> > Albert.
>
> There is no way to do what you want to do.
> MSDOS does not know anything about uid and similars

Of course, I think we all know that.

> thus neither the port nor
> the c library supports them in the way it is known from unix.  All versions
> of this port have relayed on the getuid and setuid functions provided by the
> library.  Because there is nothing like uid and alike on MSDOS these functions
> emulate them for porting purposes with hard coded values.  In the case of uid/gid
> the value is 42 when read by getuid and expects an uid of 42 when set by setuid;
> any different value will make setuid fail with EPERM.

I understand.

> Currently I have no intentions to update the bash port providing such an uid/gid
> emulation.  I even would not really know how to implement it in a way that it
> becomes a serious emulation of the unix functionality completely missed on MSDOS.

It doesn't need to be "serious".  It does, in my mind, have to be configurable.

> If you are completely despaired to have a root uid behaviour, you will have
> to modify the code of the [g|s]etui() functions of the library in such a way
> that they read a defined environment variable that defines the current uid/gid
> to be used.

Right.  Using the environment variables sounds like a reasonable solution.

> With this modified libc.a you can then recompile the bash port and
> see what happens.  But it is clear that no other program than the recompiled
> bash port will know about this modified g|s]etui().  In the worst case you
> would have to recompile also the shell utilities and file utilities and some
> other ports more.  And if they really behave as root user mode on plain DOS
> needs to be investigated.
> If all this is worth to be done must be decided by you.  I am also not really
> convinced that this will work at all.

I used a shortcut solution.  I have a utility program called HIEW.EXE,
which can display a file in hex, ASCII, and 16/32-bit assembly
language, and also edit them.

First, I did this:
C:\djgpp\lib\x>ar -xov ../libc.a getuid.o
x - getuid.o

Examining getuid.o, I found out that the relevant machine code is
0xB8,2A,00,00,00 for "mov eax, 42".  I patched BASH, the C-library
(libc.a), and the "id.exe" utility, replacing 0x2A with 00.  I also
replaced "dosuser\0" with "root\0er\0".  I left the group name as
"dos" for obvious reasons.

Result:
C:\djgpp\lib\x>bash
bash-2.04# id
uid=0(root) gid=0(dos)
bash-2.04#

But in the longer term, this should be fixed in the C library.  I
guess it is easy enough that I could even do it myself.  We'll see.

Cheers,
Albert.

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