linux-kernel - Re: [RFC PATCH v19 1/5] exec: Add a new AT

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CALmYWFu_JFyuwYhDtEDWxEob8JHFSoyx_SCcsRVKqSYyyw30Rg@mail.gmail.com>
Date: Mon, 8 Jul 2024 09:08:29 -0700
From: Jeff Xu <jeffxu@...gle.com>
To: Florian Weimer <fweimer@...hat.com>
Cc: Mickaël Salaün <mic@...ikod.net>, 
	Al Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, 
	Kees Cook <keescook@...omium.org>, Linus Torvalds <torvalds@...ux-foundation.org>, 
	Paul Moore <paul@...l-moore.com>, "Theodore Ts'o" <tytso@....edu>, 
	Alejandro Colomar <alx.manpages@...il.com>, Aleksa Sarai <cyphar@...har.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Andy Lutomirski <luto@...nel.org>, 
	Arnd Bergmann <arnd@...db.de>, Casey Schaufler <casey@...aufler-ca.com>, 
	Christian Heimes <christian@...hon.org>, Dmitry Vyukov <dvyukov@...gle.com>, 
	Eric Biggers <ebiggers@...nel.org>, Eric Chiang <ericchiang@...gle.com>, 
	Fan Wu <wufan@...ux.microsoft.com>, Geert Uytterhoeven <geert@...ux-m68k.org>, 
	James Morris <jamorris@...ux.microsoft.com>, Jan Kara <jack@...e.cz>, 
	Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>, 
	Jordan R Abrahams <ajordanr@...gle.com>, Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>, 
	Luca Boccassi <bluca@...ian.org>, Luis Chamberlain <mcgrof@...nel.org>, 
	"Madhavan T . Venkataraman" <madvenka@...ux.microsoft.com>, Matt Bobrowski <mattbobrowski@...gle.com>, 
	Matthew Garrett <mjg59@...f.ucam.org>, Matthew Wilcox <willy@...radead.org>, 
	Miklos Szeredi <mszeredi@...hat.com>, Mimi Zohar <zohar@...ux.ibm.com>, 
	Nicolas Bouchinet <nicolas.bouchinet@....gouv.fr>, Scott Shell <scottsh@...rosoft.com>, 
	Shuah Khan <shuah@...nel.org>, Stephen Rothwell <sfr@...b.auug.org.au>, 
	Steve Dower <steve.dower@...hon.org>, Steve Grubb <sgrubb@...hat.com>, 
	Thibaut Sautereau <thibaut.sautereau@....gouv.fr>, 
	Vincent Strubel <vincent.strubel@....gouv.fr>, Xiaoming Ni <nixiaoming@...wei.com>, 
	Yin Fengwei <fengwei.yin@...el.com>, kernel-hardening@...ts.openwall.com, 
	linux-api@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-security-module@...r.kernel.org
Subject: Re: [RFC PATCH v19 1/5] exec: Add a new AT_CHECK flag to execveat(2)

Hi

On Fri, Jul 5, 2024 at 11:03 AM Florian Weimer <fweimer@...hat.com> wrote:
>
> * Mickaël Salaün:
>
> > Add a new AT_CHECK flag to execveat(2) to check if a file would be
> > allowed for execution.  The main use case is for script interpreters and
> > dynamic linkers to check execution permission according to the kernel's
> > security policy. Another use case is to add context to access logs e.g.,
> > which script (instead of interpreter) accessed a file.  As any
> > executable code, scripts could also use this check [1].
>
> Some distributions no longer set executable bits on most shared objects,
> which I assume would interfere with AT_CHECK probing for shared objects.
> Removing the executable bit is attractive because of a combination of
> two bugs: a binutils wart which until recently always set the entry
> point address in the ELF header to zero, and the kernel not checking for
> a zero entry point (maybe in combination with an absent program
> interpreter) and failing the execve with ELIBEXEC, instead of doing the
> execve and then faulting at virtual address zero.  Removing the
> executable bit is currently the only way to avoid these confusing
> crashes, so I understand the temptation.
>
Will dynamic linkers use the execveat(AT_CHECK) to check shared
libraries too ?  or just the main executable itself.

Thanks.
-Jeff


> Thanks,
> Florian
>