Bug 14969 - getaddrinfo() with AI_ADDRCONFIG replaces ::1 with 127.0.0.1
Summary: getaddrinfo() with AI_ADDRCONFIG replaces ::1 with 127.0.0.1
Status: NEW
Alias: None
Product: glibc
Classification: Unclassified
Component: network (show other bugs)
Version: 2.15
: P2 normal
Target Milestone: ---
Assignee: Not yet assigned to anyone
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2012-12-17 17:08 UTC by Pavel Šimerda
Modified: 2020-07-16 07:52 UTC (History)
3 users (show)

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Host:
Target:
Build:
Last reconfirmed:
fweimer: security-

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Description Pavel Šimerda 2012-12-17 17:08:20 UTC 
getaddrinfo() with AI_ADDRCONFIG replaces all ::1 with 127.0.0.1 on hosts without non-loopback IPv6 addresses. See the following test result:

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether f0:de:f1:b8:6a:ee brd ff:ff:ff:ff:ff:ff
    inet 84.246.161.88/28 brd 84.246.161.95 scope global eth0

getaddrinfo host="None" hints.ai_flags=AI_ADDRCONFIG:
  ::1
  127.0.0.1
getaddrinfo host="localhost" hints.ai_flags=AI_ADDRCONFIG:
  127.0.0.1
  127.0.0.1
getaddrinfo host="127.0.0.1" hints.ai_flags=AI_ADDRCONFIG:
  127.0.0.1
getaddrinfo host="localhost4" hints.ai_flags=AI_ADDRCONFIG:
  127.0.0.1
getaddrinfo host="::1" hints.ai_flags=AI_ADDRCONFIG:
  ::1
getaddrinfo host="localhost6" hints.ai_flags=AI_ADDRCONFIG:
  127.0.0.1
getaddrinfo host="195.47.235.3" hints.ai_flags=AI_ADDRCONFIG:
  195.47.235.3
getaddrinfo host="2a02:38::1001" hints.ai_flags=AI_ADDRCONFIG:
  2a02:38::1001
getaddrinfo host="info.nix.cz" hints.ai_flags=AI_ADDRCONFIG:
  195.47.235.3
getaddrinfo host="www.google.com" hints.ai_flags=AI_ADDRCONFIG:
  173.194.39.81
  173.194.39.82
  173.194.39.80
  173.194.39.84
  173.194.39.83

Especially notable are:

getaddrinfo(localhost) -> 127.0.0.1, 127.0.0.1 (duplicate)
getaddrinfo(localhost6) -> 127.0.0.1 (wrong)

Contents of /etc/hosts:

127.0.0.1	localhost localhost4
::1		localhost localhost6

Looks like some sort of black magic someone was trying to solve something.
Comment 1 Pavel Šimerda 2012-12-17 17:09:23 UTC 
Testing script:

#!/usr/bin/python3
import sys
from socket import *
hosts = [
    None,
    "localhost",
    "127.0.0.1",
    "localhost4",
    "::1",
    "localhost6",
    "195.47.235.3",
    "2a02:38::1001",
    "info.nix.cz",
    "www.google.com",
]
for host in hosts:
    print("getaddrinfo host=\"{}\" hints.ai_flags=AI_ADDRCONFIG:".format(host))
    try:
        for item in getaddrinfo(host, "http", AF_UNSPEC, SOCK_STREAM, SOL_TCP, AI_ADDRCONFIG):
            print("  {}".format(item[4][0]))
    except gaierror as error:
    	print("  !! {} !!".format(error))
Comment 2 Alex Grönholm 2020-07-16 07:52:01 UTC 
This is what the attached script gives me now (Fedora 32, Glibc 2.31):

getaddrinfo host="None" hints.ai_flags=AI_ADDRCONFIG:
  ::1
  127.0.0.1
getaddrinfo host="localhost" hints.ai_flags=AI_ADDRCONFIG:
  ::1
  127.0.0.1
getaddrinfo host="127.0.0.1" hints.ai_flags=AI_ADDRCONFIG:
  127.0.0.1
getaddrinfo host="localhost4" hints.ai_flags=AI_ADDRCONFIG:
  127.0.0.1
getaddrinfo host="::1" hints.ai_flags=AI_ADDRCONFIG:
  ::1
getaddrinfo host="localhost6" hints.ai_flags=AI_ADDRCONFIG:
  ::1
getaddrinfo host="195.47.235.3" hints.ai_flags=AI_ADDRCONFIG:
  195.47.235.3
getaddrinfo host="2a02:38::1001" hints.ai_flags=AI_ADDRCONFIG:
  2a02:38::1001
getaddrinfo host="info.nix.cz" hints.ai_flags=AI_ADDRCONFIG:
  2a02:38::1001
  195.47.235.3
getaddrinfo host="www.google.com" hints.ai_flags=AI_ADDRCONFIG:
  2a00:1450:400f:809::2004
  172.217.21.132

So the output is fine now.
HOWEVER, if I query with family=AF_INET, I still get two results:
[(<AddressFamily.AF_INET: 2>, <SocketKind.SOCK_STREAM: 1>, 6, '', ('127.0.0.1', 0)),
 (<AddressFamily.AF_INET: 2>, <SocketKind.SOCK_STREAM: 1>, 6, '', ('127.0.0.1', 0))]