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Date: Thu, 27 Feb 2020 09:45:23 -0500
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: getaddrinfo(3) with AI_V4MAPPED and AI_ALL flags

On Thu, Feb 27, 2020 at 01:17:20PM +0300, Alexander Scherbatiy wrote:
> Hello,
> 
> When I call getaddrinfo() with different families, SOCK_STREAM
> socktype, IPPROTO_TCP protocol, and AI_PASSIVE flag the result is
> the same on the Alpine Linux 3.11.3 and Ubuntu 19.10 (the code
> sample is below):
> 
> ----------------
> 
> family: AF_UNSPEC, flags: AI_PASSIVE
> AF_INET  IPv4 addr '0.0.0.0'
> AF_INET6 IPv6 addr '::'
> 
> family: AF_INET,   flags: AI_PASSIVE
> AF_INET  IPv4 addr '0.0.0.0'
> 
> family: AF_INET6,  flags: AI_PASSIVE
> AF_INET6 IPv6 addr '::'
> 
> ----------------
> 
> When I use getaddrinfo() with AF_INET6 family and additional
> AI_V4MAPPED | AI_ALL (return both IPv6 and IPv4-mapped IPv6
> addresses) flags the result on Ubuntu contains only IPv6 '::'
> address:
> 
> ----------------
> 
> family: AF_INET6,  flags: AI_PASSIVE | AI_V4MAPPED | AI_ALL
> AF_INET6 IPv6 addr '::'
> 
> ----------------
> 
> whereas the result on Alpine Linux contains both IPv4-mapped IPv6
> addresses '::ffff:0.0.0.0' and  IPv6 '::'
> 
> ----------------
> 
> family: AF_INET6,  flags: AI_PASSIVE | AI_V4MAPPED | AI_ALL
> AF_INET6 IPv6 addr '::ffff:0.0.0.0'
> AF_INET6 IPv6 addr '::'
> 
> ----------------
> 
> Is it expected behavior?
> 
> I use Alpine Linux 3.11.3 from docker with musl libc (x86_64).

The musl behavior is as intended and I think it's more correct. If
net.ipv6.bindv6only sysctl is enabled, binding using the glibc results
would fail to accept ipv4 connections.

Rich

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