svn commit: r334543 - head/usr.bin/top

[Ian Lepore]

On Sun, 2018-06-03 at 14:33 -0700, Rodney W. Grimes wrote:
> > 
> > On Sat, Jun 2, 2018 at 11:08 PM, Eitan Adler <eadler at freebsd.org> wrote:
> > 
> > > 
> > > On 2 June 2018 at 16:56, Rodney W. Grimes
> > > <freebsd at pdx.rh.cn85.dnsmgr.net> wrote:
> > > > 
> > > > > 
> > > > > Author: eadler
> > > > > Date: Sat Jun  2 22:06:27 2018
> > > > > New Revision: 334543
> > > > > URL: https://svnweb.freebsd.org/changeset/base/334543
> > > > > 
> > > > > Log:
> > > > >   top(1): chdir to / as init; remove unneeded comment
> > > > > 
> > > > >   - chdir to / to allow unmounting of wd
> > > > >   - remove warning about running top(1) as setuid. If this is a concern
> > > we
> > > > 
> > > > > 
> > > > >   should just drop privs instead.
> > > > > 
> > > > > Modified:
> > > > >   head/usr.bin/top/machine.c
> > > > >   head/usr.bin/top/top.c
> > > > > 
> > > > > Modified: head/usr.bin/top/machine.c
> > > > > ============================================================
> > > ==================
> > > > 
> > > > > 
> > > > > --- head/usr.bin/top/machine.c        Sat Jun  2 21:50:00 2018
> > > (r334542)
> > > > 
> > > > > 
> > > > > +++ head/usr.bin/top/machine.c        Sat Jun  2 22:06:27 2018
> > > (r334543)
> > > > 
> > > > > 
> > > > > @@ -1613,11 +1613,6 @@ compare_ivcsw(const void *arg1, const void *arg2)
> > > > >  /*
> > > > >   * proc_owner(pid) - returns the uid that owns process "pid", or -1 if
> > > > >   *           the process does not exist.
> > > > > - *           It is EXTREMELY IMPORTANT that this function work
> > > correctly.
> > > > 
> > > > > 
> > > > > - *           If top runs setuid root (as in SVR4), then this function
> > > > > - *           is the only thing that stands in the way of a serious
> > > > > - *           security problem.  It validates requests for the "kill"
> > > > > - *           and "renice" commands.
> > > > >   */
> > > > > 
> > > > >  int
> > > > > 
> > > > > Modified: head/usr.bin/top/top.c
> > > > > ============================================================
> > > ==================
> > > > 
> > > > > 
> > > > > --- head/usr.bin/top/top.c    Sat Jun  2 21:50:00 2018        (r334542)
> > > > > +++ head/usr.bin/top/top.c    Sat Jun  2 22:06:27 2018        (r334543)
> > > > > @@ -260,6 +260,15 @@ main(int argc, char *argv[])
> > > > >  #define CMD_order    26
> > > > >  #define CMD_pid              27
> > > > > 
> > > > > +    /*
> > > > > +     * Since top(1) is often long running and
> > > > > +     * doesn't typically care about where its running from
> > > > > +     * chdir to the root to allow unmounting of its
> > > > > +     * originall wd. Failure is alright as this is
> > > > > +     * just a courtesy for users.
> > > > > +     */
> > > > > +    chdir("/");
> > > > > +
> > > > Bad side effect of doing that is it is not hard to get a "core"
> > > > from top when run as a user, as it is going to try to write
> > > > to /, and it probably does not have permission for that.
> > > Another person made the point that other similar applications don't do
> > > this, so I just reverted it.
> > > 
> > Actually,  it was a good change.
> > 
> > I've had issues on other systems where I couldn't unmount a filesystem for
> > reasons unknown.
> lsof is your friend here.  That is the tool of choice for finding
> cwd of processes that are in directories you can not unmount.
> 

Actually, rather than lsof (which I never even bother to install
anymore), I think the newer version of this advice is to use
procstat(1) from base. For example, to see why you can't umount /foo:

  procstat -af | grep /foo

-- Ian