[vdr] creating core dumps with 1.3.42

[Ville Skyttä]

On Sun, 2006-02-19 at 15:35 +0100, Klaus Schmidinger wrote:
> Ville Skyttä wrote:
> > On Thu, 2006-02-16 at 20:01 +0100, leo2 at pec.homeip.net wrote:
> > 
> >>The current function to activate core-dumps for vdr running setuid ist only 
> >>working for kernel > 2.6.13 ( says the comment in vdr.c ).
> >>Actualy it is not working for 2.4.21 but it was easy an easy change, just 
> >>replace
> >>	prctl(PR_SET_DUMPABLE, 2, 0, 0, 0)
> >>with 
> >>	prctl(PR_SET_DUMPABLE, 1, 0, 0, 0)
> >>
> >>If you need the switch with "2" ( what does "2" mean for >2.6.13 ??)
> > 
> > 
> > It's "2" intentionally.  "1" is a "no security" mode, "2" makes the core
> > dumps readable by root only and applies additional checks.  Like the
> > comment says, "2" is available in kernels >= 2.6.13 only.  For more
> > info, see eg. the suid_dumpable description here:
> > http://marc.theaimsgroup.com/?l=linux-kernel&m=109647550421014&w=2
> > 
> > Yes, the net effect is that the unmodified VDR 1.3.42 won't produce core
> > dumps at all when not running as root with < 2.6.13 kernels, but IMO
> > that's a reasonable tradeoff, at least as far as the default is
> > concerned.
> 
> So does this mean that '1' would work on older kernels?

For some values of "work", yes ;)

> Would it be feasible to use just '1' - after all, there's not
> much security about a VDR core file.

Well, the above link contains descriptions about what 1 means.  The
documentation says "... no security is applied. This is intended for
system debugging situations only." whereas for 2 they say "...
attempting to debug problems in a normal environment".  Note that it's
not only about the file permissions or the core file's contents.  Only 2
opens the dump file with O_EXCL.  Both 1 and 2 seem to use O_NOFOLLOW
though.