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Message-ID: <20250221011310.GC1827@brightrain.aerifal.cx>
Date: Thu, 20 Feb 2025 20:13:10 -0500
From: Rich Felker <dalias@...c.org>
To: Denis Ovsienko <denis@...ienko.info>
Cc: musl@...ts.openwall.com
Subject: Re: musl libc seems to use case-sensitive comparison for
hostnames in /etc/hosts
On Wed, Feb 19, 2025 at 08:56:17PM +0000, Denis Ovsienko wrote:
> Hello all.
>
> $ /usr/lib/libc.so
> musl libc (aarch64)
> Version 1.2.5
> Dynamic Program Loader
> Usage: /usr/lib/libc.so [options] [--] pathname [args]
>
> As far as I can tell, musl libc has a bug in Internet hostnames
> processing, in that it uses case-sensitive string comparison on
> hostnames that it reads from /etc/hosts. This does not apply to
> hostnames it resolves using DNS.
>
> The problem seems to be somewhere around name_from_hosts() in
> src/network/lookup_name.c. In any case, no musl code under
> src/network/ uses strcasecmp(), which hints at a likely root cause: by
> design using strcmp() to compare Internet hostnames will work correctly
> for a fraction of hostnames only.
Yes, I think this was vaguely known but ignored, probably on account
of hosts file mainly being used with manual inputs from the user in
lowercase -- not that this is an excuse for it, just likely why it
wasn't prioritized to fix.
I recall something about it coming up in the context of adding IDN,
which also sheds light on what the fix should be: not strcasecmp (a
nasty function that's underspecified and only matches what's needed
here because we took advantage of behavior outside the C locale being
unspecified) but normalizing both the input and the strings from the
hosts file so that we can strcmp.
Rich
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