Re: sshd help: setresgid() isn't working

["Neal H. Walfield" <neal@walfield.org>]

At Thu, 26 May 2005 12:08:03 +0100,
Colin Watson wrote:
> I've fixed all the Hurd build problems in openssh 1:4.0p1-1, which I'll
> be uploading to experimental shortly. However, I still can't get sshd to
> work, and it's beginning to look like a bug in glibc's Hurd support.
> 
> sshd's debug log looks like this:
> 
>   debug3: privsep user:group 101:65534
>   debug1: permanently_set_uid: 101/65534
>   permanently_set_uid: was able to restore old [e]gid
> 
> Now, I'm building this with glibc 2.3.2.ds1-22 that has weak aliases for
> setresuid and setresgid thanks to Michael Banck, so sshd is using those
> functions to switch IDs.

Interesting.  I've checked out 4.1p1 and we wouldn't use setres{u,g}id
as debian/rules includes code to make sure BROKEN_SETRES[UG]ID is
defined:

  perl -pi -e 's/.*#undef (BROKEN_SETRES[UG]ID).*/#define $$1 1/' build-deb/config.h

When I disable this code, openssh builds and runs correctly (i.e. I
don't get `permanently_set_uid: was able to restore old [e]gid').

The problem is that when we just use setreuid, we don't clear the
saved uid.  I am not sure if this is the right thing to do.

> I've attached a reduced test program which does this, and fails.

This doesn't fail on my Hurd box.

  # ./setresuid 
  # ids
  effective uids: 0(root)
  effective gids: 0(root)
  available uids: 0(root) 0(root)
  available gids: 0(root) 0(root)
  # dpkg -l libc0.3 | grep libc
  ii  libc0.3        2.3.2.ds1-22   GNU C Library: Shared libraries and Timezone

Thanks,
Neal