linux-kernel - Re: [RFC PATCH 1/2] lsm: introduce new hook security_vm

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Date: Fri, 15 Mar 2024 16:22:39 -0400
From: Paul Moore <paul@...l-moore.com>
To: Christian Göttsche <cgzones@...glemail.com>
Cc: linux-security-module@...r.kernel.org, 
	Eric Biederman <ebiederm@...ssion.com>, Kees Cook <keescook@...omium.org>, 
	Alexander Viro <viro@...iv.linux.org.uk>, Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, 
	James Morris <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>, 
	Khadija Kamran <kamrankhadijadj@...il.com>, Andrii Nakryiko <andrii@...nel.org>, 
	Casey Schaufler <casey@...aufler-ca.com>, Alexei Starovoitov <ast@...nel.org>, 
	Ondrej Mosnacek <omosnace@...hat.com>, Roberto Sassu <roberto.sassu@...wei.com>, 
	Alfred Piccioni <alpic@...gle.com>, John Johansen <john.johansen@...onical.com>, linux-mm@...ck.org, 
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] lsm: introduce new hook security_vm_execstack

On Fri, Mar 15, 2024 at 2:10 PM Christian Göttsche
<cgzones@...glemail.com> wrote:
>
> Add a new hook guarding instantiations of programs with executable
> stack.  They are being warned about since commit 47a2ebb7f505 ("execve:
> warn if process starts with executable stack").  Lets give LSMs the
> ability to control their presence on a per application basis.
>
> Signed-off-by: Christian Göttsche <cgzones@...glemail.com>
> ---
>  fs/exec.c                     |  4 ++++
>  include/linux/lsm_hook_defs.h |  1 +
>  include/linux/security.h      |  6 ++++++
>  security/security.c           | 13 +++++++++++++
>  4 files changed, 24 insertions(+)

Looking at the commit referenced above, I'm guessing the existing
security_file_mprotect() hook doesn't catch this?

> diff --git a/fs/exec.c b/fs/exec.c
> index 8cdd5b2dd09c..e6f9e980c6b1 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -829,6 +829,10 @@ int setup_arg_pages(struct linux_binprm *bprm,
>         BUG_ON(prev != vma);
>
>         if (unlikely(vm_flags & VM_EXEC)) {
> +               ret = security_vm_execstack();
> +               if (ret)
> +                       goto out_unlock;
> +
>                 pr_warn_once("process '%pD4' started with executable stack\n",
>                              bprm->file);
>         }

Instead of creating a new LSM hook, have you considered calling the
existing security_file_mprotect() hook?  The existing LSM controls
there may not be a great fit in this case, but I'd like to hear if
you've tried that, and if you have, what made you decide a new hook
was the better option?

-- 
paul-moore.com