Re: [PATCH v8 3/9] seccomp: introduce writer locking

On Wed, Jun 25, 2014 at 11:07 AM, Oleg Nesterov [off-list ref] wrote:

On 06/24, Kees Cook wrote:

quoted

+static void copy_seccomp(struct task_struct *p)
+{
+#ifdef CONFIG_SECCOMP
+     /*
+      * Must be called with sighand->lock held, which is common to
+      * all threads in the group. Regardless, nothing special is
+      * needed for the child since it is not yet in the tasklist.
+      */
+     BUG_ON(!spin_is_locked(&current->sighand->siglock));
+
+     get_seccomp_filter(current);
+     p->seccomp = current->seccomp;
+
+     if (p->seccomp.mode != SECCOMP_MODE_DISABLED)
+             set_tsk_thread_flag(p, TIF_SECCOMP);
+#endif
+}

Wait. But what about no_new_privs? We should copy it as well...

Perhaps this helper should be updated a bit and moved into seccomp.c so
that seccomp_sync_threads() could use it too.

Ah! Yes. I had been thinking it had been copied during the task_struct
duplication, but that would have been before holding sighand->lock, so
it needs explicit recopying. Thanks!

-Kees

-- 
Kees Cook
Chrome OS Security