Re: [PATCH] kernel: jump_label: fix NULL dereference bug in __jump_label_mod_update()

[Kees Cook]

On Mon, Oct 1, 2018 at 1:13 AM, Ard Biesheuvel
<ard.biesheuvel@xxxxxxxxxx> wrote:
> Commit 19483677684b ("jump_label: Annotate entries that operate on
> __init code earlier") refactored the code that manages runtime
> patching of jump labels in modules that are tied to static keys
> defined in other modules or in the core kernel.
>
> In the latter case, we may iterate over the static_key_mod linked
> list until we hit the entry for the core kernel, whose 'mod' field
> will be NULL, and attempt to dereference it to get at its 'state'
> member.
>
> So let's add a non-NULL check: this forces the 'init' argument of
> __jump_label_update() to false for static keys that are defined in
> the core kernel, which is appropriate given that __init annotated
> jump_label entries in the core kernel should no longer be active
> at this point (i.e., when loading modules).
>
> Fixes: 19483677684b ("jump_label: Annotate entries that operate on ...")
> Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Jessica Yu <jeyu@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

-Kees

> ---
>  kernel/jump_label.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/jump_label.c b/kernel/jump_label.c
> index e8cf3ff3149c..14a7f9881745 100644
> --- a/kernel/jump_label.c
> +++ b/kernel/jump_label.c
> @@ -516,7 +516,7 @@ static void __jump_label_mod_update(struct static_key *key)
>                 else
>                         stop = m->jump_entries + m->num_jump_entries;
>                 __jump_label_update(key, mod->entries, stop,
> -                                   m->state == MODULE_STATE_COMING);
> +                                   m && m->state == MODULE_STATE_COMING);
>         }
>  }
>
> --
> 2.17.1
>



-- 
Kees Cook
Pixel Security