Re: [RFC PATCH 1/2] lsm: introduce new hook security_vm_execstack

[Kees Cook]

On March 15, 2024 1:22:39 PM PDT, Paul Moore <paul@xxxxxxxxxxxxxx> wrote:
>On Fri, Mar 15, 2024 at 2:10 PM Christian Göttsche
><cgzones@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx>
>> ---
>>  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?

Also, can't MDWE handle this already?
https://git.kernel.org/linus/b507808ebce23561d4ff8c2aa1fb949fe402bc61

-Kees

-- 
Kees Cook