On Wed, 2016-08-17 at 16:00 +0200, Daniel Mack wrote:

+		progp = is_ingress ? &cgrp->bpf_ingress : &cgrp->bpf_egress;
+
+		rcu_read_lock();
+		old_prog = rcu_dereference(*progp);
+		rcu_assign_pointer(*progp, prog);
+
+		if (old_prog)
+			bpf_prog_put(old_prog);
+
+		rcu_read_unlock();

This is a bogus locking strategy.

You do not want to use rcu_read_lock()/rcu_read_unlock() here, but
appropriate writer exclusion (a mutex probably, or a spinlock)

Then use rcu_dereference_protected() instead of rcu_dereference(*progp);