Re: _ftello() modification requires additional capsicum rights, breaking tcpdump and dhclient

On Wed, Sep 10, 2014 at 3:00 AM, Andrey Chernov <ache_at_freebsd.org> wrote:

> On 09.09.2014 21:53, Patrick Kelsey wrote:
> > I don't think it is worth the trouble, as given the larger pattern of
> > libc routines requiring multiple capsicum rights, it seems one will in
> > general have to have libc implementation knowledge when using it in
> > concert with capsicum.  For example, consider the limitfd() routine in
> > kdump.c, which provides rights for the TIOCGETA ioctl to be used on
> > stdout so the eventual call to isatty() via printf() will work as
> intended.
> >
> > I think the above kdump example is a good one for the subtle issues that
> > can arise when using capsicum with libc.  That call to isatty() is via a
> > widely-used internal libc routine __smakebuf().  __smakebuf() also calls
> > __swhatbuf(), which in turn calls _fstat(), all to make sure that output
> > to a tty is line buffered by default.  It would appear that programs
> > that restrict rights on stdout without allowing CAP_IOCTL and CAP_FSTAT
> > could be disabling the normally default line buffering when stdout is a
> > tty.  kdump goes the distance, but dhclient does not (restricting stdout
> > to CAP_WRITE only).
> >
> > In any event, the patch attached to my first message is seeming like the
> > way to go.
>
> Well, then commit it (if capsicum team agrees).
>
>
>
Will do - thanks for the feedback.

-Patrick