On 06/09, Andy Lutomirski wrote:
>
> On Tue, Jun 9, 2015 at 5:49 PM, Tycho Andersen
> >
> > @@ -556,6 +556,15 @@ static int ptrace_setoptions(struct task_struct *child, unsigned long data)
> > if (data & ~(unsigned long)PTRACE_O_MASK)
> > return -EINVAL;
> >
> > + if (unlikely(data & PTRACE_O_SUSPEND_SECCOMP)) {
Well, we should do this if
(data & O_SUSPEND) && !(flags & O_SUSPEND)
or at least if
(data ^ flags) & O_SUSPEND
> > + if (!config_enabled(CONFIG_CHECKPOINT_RESTORE) ||
> > + !config_enabled(CONFIG_SECCOMP))
> > + return -EINVAL;
> > +
> > + if (!capable(CAP_SYS_ADMIN))
> > + return -EPERM;
>
> I tend to think that we should also require that current not be using
> seccomp. Otherwise, in principle, there's a seccomp bypass for
> privileged-but-seccomped programs.
Andy, I simply can't understand why do we need any security check at all.
OK, yes, in theory we can have a seccomped CAP_SYS_ADMIN process, seccomp
doesn't filter ptrace, you hack that process and force it to attach to
another CAP_SYS_ADMIN/seccomped process, etc, etc... Looks too paranoid
to me.
But damn, I said many times that I won't argue ;)
> > @@ -590,6 +590,10 @@ void secure_computing_strict(int this_syscall)
> > {
> > int mode = current->seccomp.mode;
> >
> > + if (config_enabled(CONFIG_CHECKPOINT_RESTORE) &&
> > + unlikely(current->ptrace & PT_SUSPEND_SECCOMP))
> > + return;
> > +
> > if (mode == 0)
> > return;
> > else if (mode == SECCOMP_MODE_STRICT)
> > @@ -691,6 +695,10 @@ u32 seccomp_phase1(struct seccomp_data *sd)
> > int this_syscall = sd ? sd->nr :
> > syscall_get_nr(current, task_pt_regs(current));
> >
> > + if (config_enabled(CONFIG_CHECKPOINT_RESTORE) &&
> > + unlikely(current->ptrace & PT_SUSPEND_SECCOMP))
> > + return SECCOMP_PHASE1_OK;
> > +
>
> If it's not hard, it might still be nice to try to fold this into
> mode. This code is rather hot. If it would be a mess, then don't
> worry about it for now.
IMO, this would be a mess ;) At least compared to this simple patch.
Suppose we add SECCOMP_MODE_SUSPENDED. Not only this adds the problems
with detach if the tracer dies.
We need to change copy_seccomp(). And it is not clear what should we
do if the child is traced too.
We need to change prctl_set_seccomp() paths.
And even the "tracee->seccomp.mode = SECCOMP_MODE_SUSPENDED" code needs
some locking even if the tracee is stopped, we need to avoid the races
with SECCOMP_FILTER_FLAG_TSYNC from other threads.
Oleg.
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