Re: [PATCH v2 5/5] exec: Add a exec_update_mutex to replace cred_guard_mutex

[Kees Cook]

On Mon, Mar 09, 2020 at 02:02:37PM -0500, Eric W. Biederman wrote:
>     exec: Add exec_update_mutex to replace cred_guard_mutex
>     
>     The cred_guard_mutex is problematic as it is held over possibly
>     indefinite waits for userspace.  The possilbe indefinite waits for
>     userspace that I have identified are: The cred_guard_mutex is held in
>     PTRACE_EVENT_EXIT waiting for the tracer.  The cred_guard_mutex is
>     held over "put_user(0, tsk->clear_child_tid)" in exit_mm().  The
>     cred_guard_mutex is held over "get_user(futex_offset, ...")  in
>     exit_robust_list.  The cred_guard_mutex held over copy_strings.

I suspect you're not trying to make a comprehensive list here, but do
you want to mention seccomp too (since it's yet another weird case).

> [...]
>     Holding a mutex over any of those possibly indefinite waits for
>     userspace does not appear necessary.  Add exec_update_mutex that will
>     just cover updating the process during exec where the permissions and
>     the objects pointed to by the task struct may be out of sync.

Should the specific resources be pointed out here? creds, mm, ... ?

But otherwise, yup, looks sane:

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

-- 
Kees Cook