[PATCH] Tor crashes when nodes restrictions are changed at runtime
Changing nodes restrictions using a controller while Tor is doing DNS resolution could makes Tor crashes (on WinXP at least). The problem can be repeated by trying to reach a non-existent domain using Tor: curl --socks4a 127.0.0.1:9050 inexistantdomain.ext .. and changing the ExitNodes parameter through the control port before Tor returns a DNS resolution error (of course, the following command won't work directly if the control port is password protected): echo SETCONF ExitNodes=TinyTurtle | nc -v 127.0.0.1 9051
Using a non-existent domain is needed to repeat the issue so that Tor takes a few seconds for resolving the domain (which allows us to change the configuration). Tor will crash while processing the configuration change.
The bug is located in the addressmap_clear_excluded_trackexithosts method which iterates over the entries of the addresses map in order to check whether the changes made to the configuration will impact those entries. When a DNS resolving is in progress, the new_adress field of the associated entry will be set to NULL. The method doesn't expect this field to be NULL, hence the crash.
I attached a patch that fixes the problem.