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Date: Thu, 23 May 2024 09:21:17 -0400
From: Rich Felker <dalias@...c.org>
To: Collin Funk <collin.funk1@...il.com>
Cc: musl@...ts.openwall.com
Subject: Re: getusershell should ignore comments and empty lines.
On Fri, May 17, 2024 at 08:17:54PM -0700, Collin Funk wrote:
> Hello Musl maintainers,
>
> The getusershell function behaves differently from Glibc and FreeBSD.
> I believe that it should follow those implementations by ignoring
> comments and empty lines.
>
> I wrote a test for Gnulib that catches this issue. You may find it
> helpful for testing [1].
>
> On FreeBSD I have the following etc/shells:
>
> ==============================================
> # List of acceptable shells for chpass(1).
> # ftpd(8) will not allow users to connect who are not using
> # one of these shells.
>
>
>
> /bin/sh
> /bin/csh
> /bin/tcsh
> /usr/local/bin/bash
> /usr/local/bin/rbash
> /usr/local/libexec/git-core/git-shell
> ==============================================
>
> And I run the following in a Gnulib checkout:
>
> $ rm -rf testdir1 && ./gnulib-tool --create-testdir --dir testdir1 getusershell
> $ cd testdir1
> $ ./configure
> $ make
> $ ./gltests/test-getusershell
> /bin/sh
> /bin/csh
> /bin/tcsh
> /usr/local/bin/bash
> /usr/local/bin/rbash
> /usr/local/libexec/git-core/git-shell
>
> GNU libc behaves the same way. I have not checked the other BSDs but I
> assume they use the same code derived from 4.3BSD or 4.4BSD.
>
> Using an Alpine Linux virtual machine with Musl Version 1.2.4_git20230717
> and a few packages installed I have the default /etc/shells:
>
> ==============================================
> # valid login shells
> /bin/sh
> /bin/ash
> /bin/bash
> ==============================================
>
> Using the same commands listed earlier I run:
>
> $ ./gltests/test-getusershell
> test-getusershell.c:54: assertion 'ptr[0] != '#'' failed
> Aborted
>
> And after adding an empty line before the comment:
>
> $ ./gltests/test-getusershell
> test-getusershell.c:55: assertion 'ptr[0] != '\0'' failed
> Aborted
>
> Let me know if you have any questions. The FreeBSD shells(5) man page
> is pretty good and might be helpful [2]. Here is a link to their
> implementation incase that helps too [3].
It says:
"A hash mark (``#'') indicates the beginning of a comment;
subsequent characters up to the end of the line are not
interpreted by the routines which search the file."
This isn't very clear whether # is only a comment on the beginning of
a line (after potential whitespace?) or whether # appearing in a line
with a shell pathname is a comment or part of the pathname. If it's a
comment, it's not clear if whitespace before it is part of the shell
pathname -- e.g. does "/bin/sh # best shell" define "/bin/sh" or
"/bin/sh " as the shell pathname?
It sounds like nobody ever thought about whitespace, quoting, or
rigorous comment syntax here...
Rich
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