Use asyncio to avoid blocking sock.getaddrinfo

when DNS resolution fails.

Author: tesuji

CHANGELOG.md

@@ -74,6 +74,7 @@ The table below shows which release corresponds to each branch, and what date th
 
 ## 5.0.0 (`dev`)
 
+- [#2541][2541] Fix blocking `tube.remote()` when DNS resolution fail.
 - [#2519][2519] Drop Python 2.7 support / Require Python 3.10
 - [#2507][2507] Add `+LINUX` and `+WINDOWS` doctest options and start proper testing on Windows
 - [#2522][2522] Support starting a kitty debugging window with the 'kitten' command
@@ -84,6 +85,7 @@ The table below shows which release corresponds to each branch, and what date th
 - [#2530][2530] Do NOT error when passing directory arguments in `checksec` commandline tool.
 - [#2529][2529] Add LoongArch64 support
 
+[2541]: https://github.com/Gallopsled/pwntools/pull/2541
 [2519]: https://github.com/Gallopsled/pwntools/pull/2519
 [2507]: https://github.com/Gallopsled/pwntools/pull/2507
 [2522]: https://github.com/Gallopsled/pwntools/pull/2522

pwnlib/tubes/remote.py

@@ -1,6 +1,7 @@
 from __future__ import absolute_import
 from __future__ import division
 
+import asyncio
 import socket
 import socks
 
@@ -109,8 +110,17 @@ def _connect(self, fam, typ):
         sock    = None
         timeout = self.timeout
 
+        async def resolve_hostname(host, port, fam=0, typ=0, proto=0, flags=0):
+            loop = asyncio.get_event_loop()
+            result = await loop.getaddrinfo(host, port, family=fam, type=typ, proto=proto, flags=flags)
+            return result
+
         with self.waitfor('Opening connection to %s on port %s' % (self.rhost, self.rport)) as h:
-            for res in socket.getaddrinfo(self.rhost, self.rport, fam, typ, 0, socket.AI_PASSIVE):
+            # Using asyncio to avoid blocking when DNS resolution fail. It's probably better
+            # to use async all the ways to `sock.connect`. However, let's keep the changes
+            # small until we have the needs.
+            hostnames = asyncio.run(resolve_hostname(self.rhost, self.rport, fam, typ, 0, socket.AI_PASSIVE))
+            for res in hostnames:
                 self.family, self.type, self.proto, _canonname, sockaddr = res
 
                 if self.type not in [socket.SOCK_STREAM, socket.SOCK_DGRAM]: