linux-kernel - Re: Userspace regression in LTS and stable kernels

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Message-ID: <CAFLxGvwpuxKF4UWdsULwQWo7kgVLMNHC=77dN+w-A0a6avrAXA@mail.gmail.com>
Date:   Thu, 14 Feb 2019 00:36:29 +0100
From:   Richard Weinberger <richard.weinberger@...il.com>
To:     Samuel Dionne-Riel <samuel@...nne-riel.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        graham@...hamc.com, Oleg Nesterov <oleg@...hat.com>,
        Kees Cook <keescook@...omium.org>, mhocko@...e.com,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: Userspace regression in LTS and stable kernels

[CC'in relevant folks]

On Thu, Feb 14, 2019 at 12:19 AM Samuel Dionne-Riel
<samuel@...nne-riel.com> wrote:
>
> Hi,
>
> I am posting as a representative of the NixOS Linux distribution,
> about a userspace regression on 5.0-rc* which recently was backported
> to the 4.14.99, 4.19.21 and 4.20.8 current LTS and stable versions.
> The issue has been reported to the bug tracker, bug 202497, but seems
> to have gone unnoticed by the maintainers.
>
> The issue seems to break userspace for long-standing patterns in the
> NixOS distribution, with regards to use of the shebangs.
>
> Here is an example shebang causing an issue:
>
> #! /nix/store/mbwav8kz8b3y471wjsybgzw84mrh4js9-perl-5.28.1/bin/perl
> -I/nix/store/x6yyav38jgr924nkna62q3pkp0dgmzlx-perl5.28.1-File-Slurp-9999.25/lib/perl5/site_perl
> -I/nix/store/ha8v67sl8dac92r9z07vzr4gv1y9nwqz-perl5.28.1-Net-DBus-1.1.0/lib/perl5/site_perl
> -I/nix/store/dcrkvnjmwh69ljsvpbdjjdnqgwx90a9d-perl5.28.1-XML-Parser-2.44/lib/perl5/site_perl
> -I/nix/store/rmji88k2zz7h4zg97385bygcydrf2q8h-perl5.28.1-XML-Twig-3.52/lib/perl5/site_perl

This this ever work correctly? It is longer than BINPRM_BUF_SIZE.

> (The shebang was artificially wrapped spaces replaced by newlines)
>
> Another contributor tracked the regression it to commit
> 8099b047ecc431518b9bb6bdbba3549bbecdc343 in the 5.0-rc* tree.
>
> I bring no particular fix to the issue, but I believe it should at
> least be fast-tracked to a revert for the stable and LTS branches, and
> since 5.0 might drop soon, a solution worked on, or possibly a revert
> until one is figured out.

Your shebang line exceeds BINPRM_BUF_SIZE.
Before the said commit the kernel silently truncated the shebang line
(and corrupted it),
now it tells the user that the line is too long.

Thanks,
//richard