Re: Outstanding question

On Sun, 9 Feb 2003, adam morley wrote:

> On Sun, Feb 09, 2003 at 03:24:09PM +0800, Adrian Ho wrote:
> > No, you should be seeing /tcpserver/ running as root -- it spawns ftpd
> > or httpd after accepting a connection.

This is right.

> > As a one-off test, simply replace the call to httpd in your run script
> > with /usr/bin/id (or whatever utility you use to determine the real and
> > effective UIDs/GIDs on your system) and restart the service.  Then telnet
> > to your httpd port and see for yourself.  Once you're satisfied, undo
> > the above change and restart the service again.

This is incorrect advice. tcpserver does have an option to read the
UID/GID environment variables and automatically switch ids (while
waiting for connections). However, publicfile is not able to use them
because it also wants to chroot.  So it execs httpd/ftpd as root, which
chroot, chdir("."), and then drop privs. This can be clearly seen in the
strace output you provided:

> [...]
> execve("/usr/bin/httpd", ["/usr/bin/httpd", "/home/public/file"], [/* 20 vars */]) = 0
> [...]
> chdir("/home/public/file")              = 0
> chroot(".")                             = 0
> setgroups32(0x1, 0xbffffd30)            = 0
> setgid32(0x15)                          = 0
> setuid32(0x15)                          = 0

tcpserver doesn't handle chrooting automatically. And even if it did, it
would be a collosal pain since it would require .../bin/{ftpd,httpd} and
all of their dynamic libraries to be in the new root.

> Looks to me like httpd does do the proper setuid32 and setgid32 calls,
> but id does not.  Why?  Well, I looked at main.c from publicfile-0.52,
> and I found it was doing some testing with gid/uid, so I'm guessing
> thats where the setuid/setgid happen (but I could be wrong)

Right. It looks like Adrian was thinking of tcpserver's -G/-U. However,
if those are in use, the tcpserver process should show up as the ftpd id
(it drops privs after opening the listen socket).

-Peff