Based on my experience today, I'd say this is an excellent idea for any Tor relay operator.

Have been running 'tor' on the router since late November with AddressSanitizer and it has crashed exactly ONE time: Today when someone attempted to apply the OpenSSL "Heartbleed" attack against the relay.

I asked the AS devs about removing the need for mounting /proc in the 'chroot' jail and it turns out a simple call can be inserted to close /proc after AS caching of address maps is complete. Haven't created a patch for that yet, but here is the info

https://code.google.com/p/address-sanitizer/issues/detail?id=237

My current patch to direct sdtout/stderr to files is attached.

Only downside is that AS does consume a lot of memory. After a month it eats 80% of the 2G of RAM on the router. However it seems to level off there and cease growing.

At 15:04 10/31/2013 -0500, starlight.2013q4@binnacle.cx wrote:

At 18:14 10/24/2013 -0400, starlight.2013q4@binnacle.cx wrote:

...

Has anyone tried running a live relay with an image built using GCC 4.8 and -fsanitize=address?

Took an initial jab at it by compiling just 'tor' with

CFLAGS = -g -O1 -D_FORTIFY_SOURCE=2 -fstack-protector-all -Wstack-protector -fwrapv --param ssp-buffer-size=1 -fPIE -Wall -fno-strict-aliasing -fsanitize=address -fno-omit-frame-pointer

where the modified or added flags are are

-O1 -fsanitize=address -fno-omit-frame-pointer

Fired it up and is looking good so far. CPU consumption quite reasonable at below 10%, though the relay is capped at 350 Kbytes/sec (while spiking to 500+ on a regular basis). CPU hardly seems to have increased at all. Memory consumption is, of course, up substantially with 'tor' swallowing 40% of the available 2G.

Patched

src/common/util.c:finish_daemon()

to direct stdout/stderr to out/err.tor. If AS traps-out a violation the reported details will be captured.

Had to add

libasan.so.0 -> libasan.so.0.0.0 libasan.so.0.0.0 libstdc++.so.6 -> libstdc++.so.6.0.18 libstdc++.so.6.0.18

to the 'chroot' jail. Surprised to see that AS has C++ elements.

Unfortunately AS requires

/proc/self

for access to address-space map files so

mount -o bind /proc /chroot_tor/proc

is required, increasing the kernel and local process attack-surface substantially. Salved the pain with

echo "1" >/proc/sys/kernel/modules_disabled

'tor' is running on a box dedicated to routing and has no need for loading modules after boot completes.

---

Since it works well I'll probably look at compiling other components with AS in a couple of weeks. Those would primarily be

openssl libevent zlib

Though a ball-of-yarn dimension exists in that one should probably also look into compiling

glibc

with AS as well--a nightmare I suspect.

Hopefully applying AS to the 'tor' daemon has enhanced trip-wiring of much of the available the attack surface. Looking forward to running with the upcoming 'seccomp' sandbox.

On Thu, Apr 10, 2014 at 11:53 PM, starlight.2014q2@binnacle.cx wrote:

I updated the patch to

1. have AS close /proc

2. enable core dump files

One should add

/proc /chroot_tor/proc none noauto,bind 0 0

to /etc/fstab (note the 'noauto'). Then the 'tor' startup script does a

mount /chroot_tor/proc ...start tor sleep 10 umount /chroot_tor/proc

And it works like a charm. 'tor' starts up with full AddressSanitizer monitoring but with no pesky /proc file system available to potential attackers.

Attached are the patch and the /etc/rc.d/init.d/tor

I'm sold on integrating AddressSanitizer into Tor as a compile-time option. I've got a ticket for doing so #11477 (https://trac.torproject.org/projects/tor/ticket/11477). I've uploaded your patch there, and am looking into how to better integrate it. If you could make sure that the code _I_ have successfully builds Tor with AddressSanitizer when you configure --enable-compiler-hardening, that would rock.

(If you like sandboxes, and Linux, you might also like to try the seccomp2 sandbox code, once Tor 0.2.5.4-alpha is out. It's present in Tor 0.2.5.3-alpha, but it's kind of buggy.)

Also, see bug #11232 (https://trac.torproject.org/projects/tor/ticket/11232) for the stuff I found running under AddressSanitizer and ubsan already.

best wishes,

Finally got around to compiling 'openssl' and 'libevent' with AddressSanitizer. Found and patched one minor bug as a consequence

https://trac.torproject.org/projects/tor/ticket/12227

After running for a week the relay lost its guard status due to declining BWAUTH measurements. At the time Comcast seemed to be having network problems so I'm not sure if the slowdown from ASan in 'openssl' or Comcast was the cause. Buffer stats showed 80% of cells getting queued and an average delay of 380 ms the day before the guard flags was axed. Much better on earlier days. One BWAUTH had the relay at 400 KBytes/sec so I'm inclined to think the problem was Comcast.

Anyway, switched to running just 'libssl.so' with ASan and running the normal 'libcrypto.so' on the theory that the latter is CPU intensive and at least one call-level below the surface, while the former is the easier to exploit attackable-surface component. Couldn't find any CVE's mentioning 'libcrypto.so' as having an exploitable flaw --ever.

Started with new keys and it's back to being a Guard and the buffer stats are much better than even the good days from running 'libcrypto.so' with ASan.

At 23:53 4/10/2014 -0400, starlight.2014q2@binnacle.cx wrote:

I updated the patch to

1. have AS close /proc

2. enable core dump files

One should add

/proc /chroot_tor/proc none noauto,bind 0 0

to /etc/fstab (note the 'noauto'). Then the 'tor' startup script does a

mount /chroot_tor/proc ...start tor sleep 10 umount /chroot_tor/proc

And it works like a charm. 'tor' starts up with full AddressSanitizer monitoring but with no pesky /proc file system available to potential attackers.

Attached are the patch and the /etc/rc.d/init.d/tor startup script.