On 08/30/2016 12:42 AM, Daniel Borkmann wrote:
> On 08/26/2016 09:58 PM, Daniel Mack wrote:
>> This patch adds two sets of eBPF program pointers to struct cgroup.
>> One for such that are directly pinned to a cgroup, and one for such
>> that are effective for it.
>>
>> To illustrate the logic behind that, assume the following example
>> cgroup hierarchy.
>>
>> A - B - C
>> \ D - E
>>
>> If only B has a program attached, it will be effective for B, C, D
>> and E. If D then attaches a program itself, that will be effective for
>> both D and E, and the program in B will only affect B and C. Only one
>> program of a given type is effective for a cgroup.
>>
>> Attaching and detaching programs will be done through the bpf(2)
>> syscall. For now, ingress and egress inet socket filtering are the
>> only supported use-cases.
>>
>> Signed-off-by: Daniel Mack <dan...@zonque.org>
> [...]
>> +void __cgroup_bpf_update(struct cgroup *cgrp,
>> + struct cgroup *parent,
>> + struct bpf_prog *prog,
>> + enum bpf_attach_type type)
>> +{
>> + struct bpf_prog *old_prog, *effective;
>> + struct cgroup_subsys_state *pos;
>> +
>> + old_prog = xchg(cgrp->bpf.prog + type, prog);
>> +
>> + if (prog)
>> + static_branch_inc(&cgroup_bpf_enabled_key);
>> +
>> + if (old_prog) {
>> + bpf_prog_put(old_prog);
>> + static_branch_dec(&cgroup_bpf_enabled_key);
>> + }
>> +
>> + effective = (!prog && parent) ?
>> + rcu_dereference_protected(parent->bpf.effective[type],
>> + lockdep_is_held(&cgroup_mutex)) :
>> + prog;
>> +
>> + css_for_each_descendant_pre(pos, &cgrp->self) {
>> + struct cgroup *desc = container_of(pos, struct cgroup, self);
>> +
>> + /* skip the subtree if the descendant has its own program */
>> + if (desc->bpf.prog[type] && desc != cgrp)
>> + pos = css_rightmost_descendant(pos);
>> + else
>> + rcu_assign_pointer(desc->bpf.effective[type],
>> + effective);
>> + }
>
> Shouldn't the old_prog reference only be released right here at the end
> instead of above (otherwise this could race)?
Yes, that's right. Will change as well. Thanks for spotting!
Daniel
