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

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Message-ID: <CALmYWFvkUnevm=npBeaZVkK_PXm=A8MjgxFXkASnERxoMyhYBg@mail.gmail.com>
Date: Mon, 8 Jul 2024 09:40:45 -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>, 
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	Vincent Strubel <vincent.strubel@....gouv.fr>, Xiaoming Ni <nixiaoming@...wei.com>, 
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	linux-security-module@...r.kernel.org
Subject: Re: [RFC PATCH v19 1/5] exec: Add a new AT_CHECK flag to execveat(2)

On Mon, Jul 8, 2024 at 9:26 AM Florian Weimer <fweimer@...hat.com> wrote:
>
> * Jeff Xu:
>
> > Will dynamic linkers use the execveat(AT_CHECK) to check shared
> > libraries too ?  or just the main executable itself.
>
> I expect that dynamic linkers will have to do this for everything they
> map.
Then all the objects (.so, .sh, etc.) will go through  the check from
execveat's main  to security_bprm_creds_for_exec(), some of them might
be specific for the main executable ?
e.g. ChromeOS uses security_bprm_creds_for_exec to block executable
memfd [1], applying this means automatically extending the block to
the .so object.

I'm not sure if other LSMs need to be updated ?  e.g.  will  SELINUX
check for .so with its process transaction policy ?

[1] https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/3834992

-Jeff


> Usually, that does not include the maim program, but this can
> happen with explicit loader invocations (“ld.so /bin/true”).
>
> Thanks,
> Florian
>