Torrc parser crashing for long ExitPolicy lists

[hellais]

While running tor as a relay and having a long (300 lines) list of ExitPolicy directives in the torrc file I get the following error:
Jan 09 19:12:55.541 [warn] router_dump_router_to_string(): Bug: descriptor policy_write_item ran out of room!
Jan 09 19:12:55.541 [warn] router_rebuild_descriptor(): Bug: Couldn't generate router descriptor.

And Tor will not start.

Steps to reproduce:

• Add 200-300 lines of ExitPolicy directives

for example:

ExitPolicy reject 217.169.96.0/20:*, reject 217.169.112.0/20:*, reject 217.170.224.0/20:*
ExitPolicy reject 217.171.32.0/20:*, reject 217.171.160.0/20:*, reject 217.172.0.0/20:*
ExitPolicy reject 217.172.192.0/19:*, reject 217.174.112.0/20:*, reject 217.174.128.0/20:*
...

• Start tor
• cat /var/log/tor/log

Jan 09 19:12:00.938 [warn] router_dump_router_to_string(): Bug: descriptor policy_write_item ran out of room!
Jan 09 19:12:00.938 [warn] router_rebuild_descriptor(): Bug: Couldn't generate router descriptor.

[hellais]

UPDATE:
I now noticed that this is issue is also partly discussed in this ticket:
https://trac.torproject.org/projects/tor/ticket/993

And I have encountered this issue while trying to block traffic to specific countries.
In case you need it to reproduce the issue you can find my script here:
​https://github.com/hellais/blockfinder/blob/master/torexit.py

[Sebastian]

Reproducing this is no problem; it is a known design limitation. I'm going to close this bug and add a reference to bug #993. I'm afraid that a fix will take a long time, because a lot of design is involved.