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Re: [PATCH] tzset robustness [BZ#17715]

On Thu, Jan 15, 2015 at 02:45:55PM +0100, Florian Weimer wrote:
> On 01/15/2015 02:39 PM, Rich Felker wrote:
> >On Wed, Jan 14, 2015 at 11:11:42PM +0100, Florian Weimer wrote:
> >>This patch removes two different unbounded alloca calls, and also
> >>fixes the TZ parser issue identified here:
> >>
> >>
> >>
> >>This is not my preferred approach.  I would rather like to sanitize
> >>TZ in AT_SECURE mode, so that specifying a file from a non-default
> >>TZDIR does not work.  However, this alternative approach is a bit
> >>involved because the current setup code is not fit to handle
> >>content-dependent environment variable scrubbing.
> >
> >Doing the scrubbing in the dynamic linker does not seem appropriate
> >anyway. It wouldn't solve the problem for static-linked binaries and
> I have working scrubbing for statically linked binaries, I think.
> >it would wrongly remove environment entries rather than just ignoring
> >them. Instead, tzset should be doing its own path enforcement based on
> >the presence of getauxval(AT_SECURE) or similar (e.g. the proposed
> >issetugid function).
> We already do that, but we aren't consistent about it: We scrub
> TZDIR unconditionally (which is cleared in AT_SECURE mode), but we
> pass TZ variables containing absolute paths to subprocesses.  The
> latter means that the TZDIR scrubbing isn't effective.

I fail to see how removing env vars behind the program's back is
conforming. I understand that the _intent_ is to improve security, but
IMO any contract violation such as this is a potential cause of
vulnerabilities in itself (e.g. as a silly example, suppose the child
process you were executing is a tool that examines the environment and
exits with 0/1 to tell if the environment contained anything


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