From 719b78a5674f15fef2e4a56484614657fd759978 Mon Sep 17 00:00:00 2001 From: Jakub Sitnicki Date: Fri, 11 Oct 2019 10:29:45 +0200 Subject: flow_dissector: Allow updating the flow dissector program atomically 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 Signed-off-by: Daniel Borkmann Reviewed-by: Stanislav Fomichev Acked-by: Martin KaFai Lau Link: https://lore.kernel.org/bpf/20191011082946.22695-2-jakub@cloudflare.com --- net/core/flow_dissector.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) (limited to 'net/core/flow_dissector.c') diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c index 6b4b88d1599d..dbf502c18656 100644 --- a/net/core/flow_dissector.c +++ b/net/core/flow_dissector.c @@ -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; -- cgit v1.2.3-59-g8ed1b