Dear all, While working on http://twistedmatrix.com/trac/ticket/8912 and the associated PR at https://github.com/twisted/twisted/pull/647 I hit a segmentation fault on a test I was preparing. I think narrowed it down Linux + Python 2, but I'm not 100% sure. Can anyone please confirm the code below segfaults on such environment? For completeness, from my tests, it works fine on Linux + Python 3, and fails with socket.error/OSError on Mac OS 10.9.5 + Python 2/3. No BSDs at hand to try out... As far as I can tell, no code in Twisted uses sendmsg in the way the code is using it. However, twisted.python.sendmsg is a public API so someone somewhere may hit this like I just did. Other than looking for confirmation, I have a fix which I included two isolated commits in the PR. Twisted project members: if this is confirmed, maybe a ticket should be created in Trac and an independent PR created, correct? Thanks in advance for any input. Regards, -- exvito -[ cut here ]---------------------------------------------------------------------- import os import socket import struct import sys from twisted.python import sendmsg if __name__ == '__main__': # This code segfaults when running with twisted/trunk commit # 98a3df200968b78bd3b985dfd4fb10a5b415d6fc on Linux Python 2 # due to a bug in src/twisted/python/_sendmsg.c and glibc's # CMSG_NXTHDR implementation. # get connected sockets s1, s2 = socket.socketpair(socket.AF_UNIX) # two CMSGs in ancillary data (no segfault with just one) ancillary = [ (socket.SOL_SOCKET, sendmsg.SCM_RIGHTS, struct.pack('i', s1.fileno())), (socket.SOL_SOCKET, sendmsg.SCM_RIGHTS, struct.pack('i', s2.fileno())), ] expected = { 2: 'Expecting to segfault.', 3: 'Should not segfault.', } print expected.get(sys.version_info.major, 'Unexpected Python version.') retval = sendmsg.sendmsg(s1, data=b'some data', ancillary=ancillary) print 'Did not segfault.' -[ cut here ]----------------------------------------------------------------------