kernel BUG at kernel/cred.c:434!

[Oleg Nesterov]

On 04/15, Paul Moore wrote:
>
> On Mon, Apr 15, 2019 at 9:43 AM Oleg Nesterov <oleg at redhat.com> wrote:
> > Well, acct("/proc/self/attr/current") doesn't look like a good idea, but I do
> > not know where should we put the additional check... And probably
> > "echo /proc/self/attr/current > /proc/sys/kernel/core_pattern" can hit the
> > same problem, do_coredump() does override_creds() too.
> >
> > May be just add
> >
> >         if (current->cred != current->real_cred)
> >                 return -EACCES;
> >
> > into proc_pid_attr_write(), I dunno.
>
> Is the problem that do_acct_process() is calling override_creds() and
> the returned/old credentials are being freed before do_acct_process()
> can reinstall the creds via revert_creds()?  Presumably because the
> process accounting is causing the credentials to be replaced?

Afaics, the problem is that do_acct_process() does override_creds() and
then __kernel_write(). Which calls proc_pid_attr_write(), which in turn calls
selinux_setprocattr(), which does another prepare_creds() + commit_creds();
and commit_creds() hits

	BUG_ON(task->cred != old);

Oleg.