August 2019 - tor-dev - lists.torproject.org

Enhanced Tor Browser sandboxing upstreaming
by procmem＠riseup.net 24 Aug '19

24 Aug '19

Hi. We aim to make enhanced sandboxing for Tor Browser widely available on Linux that's well maintained in the long term. We would appreciate it if TBB team provides the currently developed Apparmor and firejail profiles below from your repos and run unit testing and check/fix any breakages with updated browser versions. It turns out there is an advantage to stacking both Apparmor and Firejail. Firejail doesn’t offer nearly as good file path whitelisting as AppArmor. Firejail also can’t do many things AppArmor can such as managing ptrace or signals, yet firejail can use xpra to isolate Tor Browser's access to X, pulseaudio and the clipboard. The Firejail package included in Debian stable cannot keep pace with the needed changes as Tor Browser continues to change. Stacking is also a good defense in depth. If there’s a vulnerability in Firejail then AppArmor will still restrict the application or vice versa. Firejail provides a maintained official profile for Tor Browser [0]. We have a Apparmor profile that we've maintained for years [1]. [0] https://github.com/netblue30/firejail/blob/master/etc/start-tor-browser.pro… [1] https://github.com/Whonix/apparmor-profile-torbrowser

1 0

TBB Memory Allocator choice fingerprint implications
by procmem＠riseup.net 21 Aug '19

21 Aug '19

Question for the Tor Browser experts. Do you know if it is possible to remotely fingerprint the browser based on the memory allocator it is using? (via JS or content rendering) We are thinking of switching Tor Browser to use the minimalist and security oriented hardened_malloc written by Daniel Micay. Thanks.

10 17

[prop305] Introduction Point Behavior
by David Goulet 20 Aug '19

20 Aug '19

Greetings, This is part of the many discussions about proposal 305 which is the ESTABLISH_INTRO DoS defenses cell extension. Implementation is close to done and under review in ticket #30924. However, there is one part that is yet to be cleared out. asn and I thought it would be better to bring it to tor-dev@ to get a more informed decision. As a reminder, the service operator will be able set torrc options that are the DoS defenses parameters. Those values are validated (bound check) and then sent to an introduction point, supporting the extension (protover HSIntro=5), in the ESTABLISH_INTRO cell. The intro point then gets them and apply them only to that specific circuit. If no cell extension is seen, the intro point will honor the consensus parameters for these DoS defenses. What we want to discuss is what happened when the introduction points receives bad values. What does it do with the circuit? Below is the list of possible bad values and the proposed behavior: 1) One of the paramater (at this point in time, only 2 exists) is out of bound that is above INT32_MAX. Behavior: We propose to ignore the cell extension, and fallback to follow the consensus parameters. Keeping the circuit alive and working. The reason for this is because if let say the intro point would close the circuit due to "bad protocol", then the service would open a new circuit to an intro point supporting the extension and it would fail again. Effectively turning the service into a "zombie" and "DoS" weapon itself ;). At this point, there is really no reason on why the service would send bad values since torrc options are validated and then sent to the intro point. But this doesn't protect us from our future-developer-self making coding or protocol mistake ;). 2) A parameter type is unrecognized. This one is mostly about forward compatibility. Behavior: Ignore the parameter type, and continue parsing the cell extension. If all the right parameters are found, apply defenses. 3) None or 1 parameter out of 2 is given. Behavior: This would be considered bad protocol so it would be like (1) where the intro point uses the consensus parameters. 4) <insert whatever case you can think about> So, for (1) and (3), there lies mostly the discussion. There is no way to send feedback to the service if a problem occurred and that the DoS defenses weren't applied due to reason X. If we had that, we could not only try to warn the operator (log or control event) but make tor smarter when an error is returned so it doesn't try to infinity other intro points with values that makes them fail. One avenue there is to pass down such error code into the INTRO_ESTABLISHED cell with probably a new extension. That requires more work and likely either extending prop305 or a new proposal. Thus, what is the minimal viable product here we are ok with? I'm leaning towards not closing the circuit and falling back on the consensus parameters. And at some point in time, we'll be able to implement the INTRO_ESTABLISHED response. In the meantime, there is little chances that tor vanilla start sending bad values since they are validated from the torrc file. Cheers! David -- eHE50zZRZOX3zLNHdPwN5gGQBUvDnfGyOuYr/afK2XY=

3 2

Re: [tor-dev] TBB Memory Allocator choice fingerprint implications
by procmem＠riseup.net 17 Aug '19

17 Aug '19

*On Sat, 17 Aug 2019 at**21:17, Tom Ritter* <tom at ritter.vg <mailto:tor-dev%40lists.torproject.org?Subject=Re%3A%20%5Btor-dev%5D%20TBB%20Memory%20Allocator%20choice%20fingerprint%20implications&In-Reply-To=%3CCA%2BcU71%3DPeZGCAJNsPQy9QpKY9%3Dwz3vPdW8QKruF_ZwyanoyYzQ%40mail.gmail.com%3E>> wrote: > On Sat, 17 Aug 2019 at 15:06, procmem at riseup.net <https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-dev> <procmem at riseup.net <https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-dev>> wrote: > >/Question for the Tor Browser experts. Do you know if it is possible to />/remotely fingerprint the browser based on the memory allocator it is />/using? (via JS or content rendering) / > Fingerprint what aspect of the browser/machine? I'm not really sure (I'm of the opinion it should not matter) and so I'm curious as to what could be affected if anything. Some members of our team are divided about making it the default because of unknown consequences which is what I'm trying to clear up. > >/We are thinking of switching Tor Browser to use the minimalist and />/security oriented hardened_malloc written by Daniel Micay. Thanks. / > I wouldn't advise giving up partitioning for.... what exactly? What > features does this allocator have that 68's jemalloc doesn't? > > -tom So the original suggestion [0] was prompted by past research done by the Tor Browser team for a jemalloc alternative. [1] Hardened_malloc wasn't around back then so it may be a worthy alternative for you guys to switch to too. Hardened_malloc has a partitioned heap among many other defenses implemented if I understand their label correctly (please see "Security properties" section in [2]). Also available on ARM. [0] https://forums.whonix.org/t/hardened-malloc/7474 [1] https://trac.torproject.org/projects/tor/ticket/10281 [2] https://github.com/GrapheneOS/hardened_malloc *** PS. A related debate is on whether we should enable Apparmor and Firejail sandboxing for Tor Browser by default, but again we don't know if restriction to resources and file paths on the machine is something that is remotely detectable as an anomaly or not, ruining the fingerprint in the process. Input is appreciated. related thread: https://forums.whonix.org/t/tor-browser-hardening-hardened-malloc-firejail-…

1 0