Re: [tor-relays] running Tor relay live with AddressSanitizer

[starlight.2013q4@xxxxxxxxxxx]

At 18:14 10/24/2013 -0400, starlight.2013q4@xxxxxxxxxxx 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.

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