bpf, netns: Keep a list of attached bpf_link's

To support multi-prog link-based attachments for new netns attach types, we
need to keep track of more than one bpf_link per attach type. Hence,
convert net->bpf.links into a list, that currently can be either empty or
have just one item.

Instead of reusing bpf_prog_list from bpf-cgroup, we link together
bpf_netns_link's themselves. This makes list management simpler as we don't
have to allocate, initialize, and later release list elements. We can do
this because multi-prog attachment will be available only for bpf_link, and
we don't need to build a list of programs attached directly and indirectly
via links.

No functional changes intended.

Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20200625141357.910330-4-jakub@cloudflare.com

diff --git a/include/net/netns/bpf.h b/include/net/netns/bpf.h
index a5015bda997981cdc9b587f99c175b2a004f8de9..0ca6a1b8718533adf2f37223bf4d8955df151246 100644 (file)
--- a/include/net/netns/bpf.h
+++ b/include/net/netns/bpf.h
@@ -15,7 +15,7 @@ struct netns_bpf {
        /* Array of programs to run compiled from progs or links */
        struct bpf_prog_array __rcu *run_array[MAX_NETNS_BPF_ATTACH_TYPE];
        struct bpf_prog *progs[MAX_NETNS_BPF_ATTACH_TYPE];
-       struct bpf_link *links[MAX_NETNS_BPF_ATTACH_TYPE];
+       struct list_head links[MAX_NETNS_BPF_ATTACH_TYPE];
 };
 
 #endif /* __NETNS_BPF_H__ */

diff --git a/kernel/bpf/net_namespace.c b/kernel/bpf/net_namespace.c
index 0dba972023571edc32b3d4d637d128197d2cf716..7a34a8caf954528148c06ea557189096eee021dc 100644 (file)
--- a/kernel/bpf/net_namespace.c
+++ b/kernel/bpf/net_namespace.c
@@ -19,20 +19,12 @@ struct bpf_netns_link {
         * with netns_bpf_mutex held.
         */
        struct net *net;
+       struct list_head node; /* node in list of links attached to net */
 };
 
 /* Protects updates to netns_bpf */
 DEFINE_MUTEX(netns_bpf_mutex);
 
-/* Must be called with netns_bpf_mutex held. */
-static void __net_exit bpf_netns_link_auto_detach(struct bpf_link *link)
-{
-       struct bpf_netns_link *net_link =
-               container_of(link, struct bpf_netns_link, link);
-
-       net_link->net = NULL;
-}
-
 /* Must be called with netns_bpf_mutex held. */
 static void netns_bpf_run_array_detach(struct net *net,
                                       enum netns_bpf_attach_type type)
@@ -66,7 +58,7 @@ static void bpf_netns_link_release(struct bpf_link *link)
                goto out_unlock;
 
        netns_bpf_run_array_detach(net, type);
-       net->bpf.links[type] = NULL;
+       list_del(&net_link->node);
 
 out_unlock:
        mutex_unlock(&netns_bpf_mutex);
@@ -225,7 +217,7 @@ int netns_bpf_prog_attach(const union bpf_attr *attr, struct bpf_prog *prog)
        mutex_lock(&netns_bpf_mutex);
 
        /* Attaching prog directly is not compatible with links */
-       if (net->bpf.links[type]) {
+       if (!list_empty(&net->bpf.links[type])) {
                ret = -EEXIST;
                goto out_unlock;
        }
@@ -279,7 +271,7 @@ static int __netns_bpf_prog_detach(struct net *net,
        struct bpf_prog *attached;
 
        /* Progs attached via links cannot be detached */
-       if (net->bpf.links[type])
+       if (!list_empty(&net->bpf.links[type]))
                return -EINVAL;
 
        attached = net->bpf.progs[type];
@@ -310,13 +302,15 @@ int netns_bpf_prog_detach(const union bpf_attr *attr)
 static int netns_bpf_link_attach(struct net *net, struct bpf_link *link,
                                 enum netns_bpf_attach_type type)
 {
+       struct bpf_netns_link *net_link =
+               container_of(link, struct bpf_netns_link, link);
        struct bpf_prog_array *run_array;
        int err;
 
        mutex_lock(&netns_bpf_mutex);
 
        /* Allow attaching only one prog or link for now */
-       if (net->bpf.links[type]) {
+       if (!list_empty(&net->bpf.links[type])) {
                err = -E2BIG;
                goto out_unlock;
        }
@@ -345,7 +339,7 @@ static int netns_bpf_link_attach(struct net *net, struct bpf_link *link,
        run_array->items[0].prog = link->prog;
        rcu_assign_pointer(net->bpf.run_array[type], run_array);
 
-       net->bpf.links[type] = link;
+       list_add_tail(&net_link->node, &net->bpf.links[type]);
 
 out_unlock:
        mutex_unlock(&netns_bpf_mutex);
@@ -404,24 +398,34 @@ out_put_net:
        return err;
 }
 
+static int __net_init netns_bpf_pernet_init(struct net *net)
+{
+       int type;
+
+       for (type = 0; type < MAX_NETNS_BPF_ATTACH_TYPE; type++)
+               INIT_LIST_HEAD(&net->bpf.links[type]);
+
+       return 0;
+}
+
 static void __net_exit netns_bpf_pernet_pre_exit(struct net *net)
 {
        enum netns_bpf_attach_type type;
-       struct bpf_link *link;
+       struct bpf_netns_link *net_link;
 
        mutex_lock(&netns_bpf_mutex);
        for (type = 0; type < MAX_NETNS_BPF_ATTACH_TYPE; type++) {
                netns_bpf_run_array_detach(net, type);
-               link = net->bpf.links[type];
-               if (link)
-                       bpf_netns_link_auto_detach(link);
-               else if (net->bpf.progs[type])
+               list_for_each_entry(net_link, &net->bpf.links[type], node)
+                       net_link->net = NULL; /* auto-detach link */
+               if (net->bpf.progs[type])
                        bpf_prog_put(net->bpf.progs[type]);
        }
        mutex_unlock(&netns_bpf_mutex);
 }
 
 static struct pernet_operations netns_bpf_pernet_ops __net_initdata = {
+       .init = netns_bpf_pernet_init,
        .pre_exit = netns_bpf_pernet_pre_exit,
 };