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


On 01/16/2015 09:27 PM, Carlos O'Donell wrote:
>>> 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
>> dangerous).
> 
> I can't help but agree. Removing env vars is a bad idea, ignoring them
> is the only way I'd handle this.

On the other hand, looking at TZDIR at all is non-confirming as well.

It is certainly easier not to scrub the TZ variable because no
additional patch is required.  But I'm worried that the TZ parser
crosses a trust boundary, and we'll have to patch it again (and again).
 Ulrich already tried to robustify the parser in commit
97ac2654b2d831acaa18a2b018b0736245903fd2, BZ #13506, but missed a few
corner cases.  I don't feel very confident that my latest patch
addresses all remaining issues.

-- 
Florian Weimer / Red Hat Product Security


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