On Fri, Oct 4, 2019 at 8:58 AM Stanislav Fomichev <sdf@xxxxxxxxxx> wrote:
>
> Always use init_net flow dissector BPF program if it's attached and fall
> back to the per-net namespace one. Also, deny installing new programs if
> there is already one attached to the root namespace.
> Users can still detach their BPF programs, but can't attach any
> new ones (-EEXIST).
>
> Cc: Petar Penkov <ppenkov@xxxxxxxxxx>
> Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
> ---
Looks good, but see my note below. Regardless:
Acked-by: Andrii Nakryiko <andriin@xxxxxx>
> Documentation/bpf/prog_flow_dissector.rst | 3 ++
> net/core/flow_dissector.c | 42 ++++++++++++++++++++---
> 2 files changed, 41 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/bpf/prog_flow_dissector.rst b/Documentation/bpf/prog_flow_dissector.rst
> index a78bf036cadd..4d86780ab0f1 100644
> --- a/Documentation/bpf/prog_flow_dissector.rst
> +++ b/Documentation/bpf/prog_flow_dissector.rst
> @@ -142,3 +142,6 @@ BPF flow dissector doesn't support exporting all the metadata that in-kernel
> C-based implementation can export. Notable example is single VLAN (802.1Q)
> and double VLAN (802.1AD) tags. Please refer to the ``struct bpf_flow_keys``
> for a set of information that's currently can be exported from the BPF context.
> +
> +When BPF flow dissector is attached to the root network namespace (machine-wide
> +policy), users can't override it in their child network namespaces.
> diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
> index 7c09d87d3269..9821e730fc70 100644
> --- a/net/core/flow_dissector.c
> +++ b/net/core/flow_dissector.c
> @@ -114,19 +114,50 @@ int skb_flow_dissector_bpf_prog_attach(const union bpf_attr *attr,
> {
> struct bpf_prog *attached;
> struct net *net;
> + int ret = 0;
>
> net = current->nsproxy->net_ns;
> mutex_lock(&flow_dissector_mutex);
> +
> + if (net == &init_net) {
> + /* BPF flow dissector in the root namespace overrides
> + * any per-net-namespace one. When attaching to root,
> + * make sure we don't have any BPF program attached
> + * to the non-root namespaces.
> + */
> + struct net *ns;
> +
> + for_each_net(ns) {
> + if (net == &init_net)
> + continue;
You don't need this condition, if something is attached to init_net,
you will return -EEXIST anyway. Or is this a performance optimization?
> +
> + if (rcu_access_pointer(ns->flow_dissector_prog)) {
> + ret = -EEXIST;
> + goto out;
> + }
> + }
> + } else {
> + /* Make sure root flow dissector is not attached
> + * when attaching to the non-root namespace.
> + */
> +
nit: extra empty line
> + if (rcu_access_pointer(init_net.flow_dissector_prog)) {
> + ret = -EEXIST;
> + goto out;
> + }
> + }
> +
> 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 */
> - mutex_unlock(&flow_dissector_mutex);
> - return -EEXIST;
> + ret = -EEXIST;
> + goto out;
> }
> rcu_assign_pointer(net->flow_dissector_prog, prog);
> +out:
> mutex_unlock(&flow_dissector_mutex);
> - return 0;
> + return ret;
> }
>
> int skb_flow_dissector_bpf_prog_detach(const union bpf_attr *attr)
> @@ -910,7 +941,10 @@ bool __skb_flow_dissect(const struct net *net,
> WARN_ON_ONCE(!net);
> if (net) {
> rcu_read_lock();
> - attached = rcu_dereference(net->flow_dissector_prog);
> + attached = rcu_dereference(init_net.flow_dissector_prog);
> +
> + if (!attached)
> + attached = rcu_dereference(net->flow_dissector_prog);
>
> if (attached) {
> struct bpf_flow_keys flow_keys;
> --
> 2.23.0.581.g78d2f28ef7-goog
>
