Re: kernel BUG at kernel/cred.c:434!

[Paul Moore]

On Wed, Apr 17, 2019 at 10:50 PM Yang Yingliang
<yangyingliang@xxxxxxxxxx> wrote:
> On 2019/4/18 8:24, Casey Schaufler wrote:
> > On 4/17/2019 4:39 PM, Paul Moore wrote:
> >>
> >> Since it looks like all three LSMs which implement the setprocattr
> >> hook are vulnerable I'm open to the idea that proc_pid_attr_write() is
> >> a better choice for the cred != read_cred check, but I would want to
> >> make sure John and Casey are okay with that.
> >>
> >> John?
> >>
> >> Casey?
> >
> > I'm fine with the change going into proc_pid_attr_write().
>
> The cred != real_cred checking is not enough.
>
> Consider this situation, when doing override, cred, real_cred and
> new_cred are all same:
>
> after override_creds()    cred == real_cred == new1_cred

I'm sorry, you've lost me.  After override_creds() returns
current->cred and current->real_cred are not going to be the same,
yes?

> after prepare_creds()     new2_cred
> after commit_creds()     becasue the check is false, so cred ==
> real_cred == new2_cred
> after revert_creds()        cred == new1_cred, real_cred == new2_cred
>
> It will cause cred != real_cred finally.

-- 
paul moore
www.paul-moore.com