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Re: [PATCH] tzset robustness [BZ#17715]
- From: Florian Weimer <fweimer at redhat dot com>
- To: Rich Felker <dalias at libc dot org>
- Cc: GNU C Library <libc-alpha at sourceware dot org>
- Date: Thu, 15 Jan 2015 14:45:55 +0100
- Subject: Re: [PATCH] tzset robustness [BZ#17715]
- Authentication-results: sourceware.org; auth=none
- References: <54B6E99E dot 4030109 at redhat dot com> <20150115133911 dot GR4574 at brightrain dot aerifal dot cx>
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:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=772705
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 ld.so 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.
--
Florian Weimer / Red Hat Product Security