4da9f87ccb
Fix undefined behaviour and application crash that might take place in some rare cases after calling evdns_base_free when there are requests in the waiting queue. Current cleanup procedure in evdns_base_free_and_unlock function includes 2 steps: 1. Finish all inflight requests. 2. Finish all waiting requests. During the first step we iterate over each list in req_heads structure and finish all requests in these lists. With current logic finishing an inflight request (function request_finished) removes it from the inflight requests container and forces a wating connection to be sent (by calling evdns_requests_pump_waiting_queue). When these new requests are sent it is possible that they will be inserted to the list in req_heads that we've already cleaned. So in some cases container of the inflight requests is not empty after this procedure and some requests are not finished and deleted. When timeouts for these requests expire evdns_request_timeout_callback is called but corresponding evdns_base has been already deleted which causes undefined behaviour and possible applicaton crash. It is interesting to note that in old versions of libevent such situation was not possible. This bug was introduced by the commit 14f84bbdc77d90b1d936076661443cdbf516c593. Before this commit nameservers were deleted before finishing the requests. Therefore it was not possible that requests from the waiting queue be sent while we finish the inflight requests.
1. BUILDING AND INSTALLATION
Autoconf
$ ./configure
$ make
$ make verify # (optional)
$ sudo make install
See Documentation/Building#Autoconf for more information
CMake (Windows)
Install CMake: https://www.cmake.org
$ md build && cd build
$ cmake -G "Visual Studio 10" .. # Or use any generator you want to use. Run cmake --help for a list
$ cmake --build . --config Release # Or "start libevent.sln" and build with menu in Visual Studio.
See Documentation/Building#Building on Windows for more information
CMake (Unix)
$ mkdir build && cd build
$ cmake .. # Default to Unix Makefiles.
$ make
$ make verify # (optional)
See Documentation/Building#Building on Unix (With CMake) for more information
Package Managers
You can download and install libevent using the vcpkg dependency manager:
git clone https://github.com/Microsoft/vcpkg.git
cd vcpkg
./bootstrap-vcpkg.sh
./vcpkg integrate install
./vcpkg install libevent
The libevent port in vcpkg is kept up to date by Microsoft team members and community contributors. If the version is out of date, please create an issue or pull request on the vcpkg repository.
2. USEFUL LINKS:
For the latest released version of Libevent, see the official website at http://libevent.org/ .
There's a pretty good work-in-progress manual up at http://www.wangafu.net/~nickm/libevent-book/ .
For the latest development versions of Libevent, access our Git repository via
$ git clone https://github.com/libevent/libevent.git
You can browse the git repository online at:
https://github.com/libevent/libevent
To report bugs, issues, or ask for new features:
Patches: https://github.com/libevent/libevent/pulls
OK, those are not really patches. You fork, modify, and hit the "Create Pull Request" button. You can still submit normal git patches via the mailing list.
Bugs, Features [RFC], and Issues: https://github.com/libevent/libevent/issues
Or you can do it via the mailing list.
There's also a libevent-users mailing list for talking about Libevent use and development:
http://archives.seul.org/libevent/users/
3. ACKNOWLEDGMENTS
The following people have helped with suggestions, ideas, code or fixing bugs.