Re: uid of user who mounts

[Steve French <smfrench@austin.rr.com>]

On Sat, 2004-07-31 at 19:31 +0200, Miklos Szeredi wrote:
> Steve French wrote:
> >
> > I confirmed what Randy had mantioned about the user= entries in mtab
> > allowing umounts (at least it works that way for a few of the local
> > filesystems I tried) but did not seem to work so well on other
> > filesystems - I had odd results on umounting my cifs mounts e.g. - after
> > adding at mount time "user=someuser" to /etc/mtab (by a minor change to
> > the mount helper mount.cifs.c, when running mount.cifs suid).  umount of
> > those mounts failed
> 
> I've seen failure to unmount only if there is no matching entry in
> /etc/fstab.  It sounds a bit too much paranoia, but who knows.
> 
> Miklos

This is getting hard to debug because the mount and umount that ship
with Fedora doesn't match the behavior of mount & umount current source
on kernel.org for the mount utils.  What I have discovered so far is
that the failure in unmount is the check in sys_umount in fs/namespace.c

        if (!capable(CAP_SYS_ADMIN))

which fails presumably because mount did not find a match in /etc/fstab
although I have tried various experiments and it looks like the umount
should have matched the /etc/mtab entry.  My guess is that the matching
rules don't work very well for filesystems unless they specify either a
physical device or name (I had been specifying a UNC name as the device,
but am experimenting with having cifs use the nfs server:export format
to see if that will make umount happier).