@@ -128,6 +128,8 @@ int skb_flow_dissector_bpf_prog_attach(const union bpf_attr *attr,
struct net *ns;
for_each_net(ns) {
+ if (ns == &init_net)
+ continue;
if (rcu_access_pointer(ns->flow_dissector_prog)) {
ret = -EEXIST;
goto out;
@@ -145,12 +147,14 @@ int skb_flow_dissector_bpf_prog_attach(const union bpf_attr *attr,
attached = rcu_dereference_protected(net->flow_dissector_prog,
lockdep_is_held(&flow_dissector_mutex));
- if (attached) {
- /* Only one BPF program can be attached at a time */
- ret = -EEXIST;
+ if (attached == prog) {
+ /* The same program cannot be attached twice */
+ ret = -EINVAL;
goto out;
}
rcu_assign_pointer(net->flow_dissector_prog, prog);
+ if (attached)
+ bpf_prog_put(attached);
out:
mutex_unlock(&flow_dissector_mutex);
return ret;
It is currently not possible to detach the flow dissector program and attach a new one in an atomic fashion, that is with a single syscall. Attempts to do so will be met with EEXIST error. This makes updates to flow dissector program hard. Traffic steering that relies on BPF-powered flow dissection gets disrupted while old program has been already detached but the new one has not been attached yet. There is also a window of opportunity to attach a flow dissector to a non-root namespace while updating the root flow dissector, thus blocking the update. Lastly, the behavior is inconsistent with cgroup BPF programs, which can be replaced with a single bpf(BPF_PROG_ATTACH, ...) syscall without any restrictions. Allow attaching a new flow dissector program when another one is already present with a restriction that it can't be the same program. Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com> --- net/core/flow_dissector.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)