[PATCH bpf-next v3 1/4] flow_dissector: Pull BPF program assignment up to bpf-netns

[Jakub Sitnicki <jakub@xxxxxxxxxxxxxx>]

Prepare for using bpf_prog_array to store attached programs by moving out
code that updates the attached program out of flow dissector.

Managing bpf_prog_array is more involved than updating a single bpf_prog
pointer. This will let us do it all from one place, bpf/net_namespace.c, in
the subsequent patch.

No functional change intended.

Acked-by: Andrii Nakryiko <andriin@xxxxxx>
Signed-off-by: Jakub Sitnicki <jakub@xxxxxxxxxxxxxx>
---
 include/net/flow_dissector.h |  3 ++-
 kernel/bpf/net_namespace.c   | 20 ++++++++++++++++++--
 net/core/flow_dissector.c    | 13 ++-----------
 3 files changed, 22 insertions(+), 14 deletions(-)

diff --git a/include/net/flow_dissector.h b/include/net/flow_dissector.h
index a7eba43fe4e4..4b6e36288ddd 100644
--- a/include/net/flow_dissector.h
+++ b/include/net/flow_dissector.h
@@ -372,7 +372,8 @@ flow_dissector_init_keys(struct flow_dissector_key_control *key_control,
 }
 
 #ifdef CONFIG_BPF_SYSCALL
-int flow_dissector_bpf_prog_attach(struct net *net, struct bpf_prog *prog);
+int flow_dissector_bpf_prog_attach_check(struct net *net,
+					 struct bpf_prog *prog);
 #endif /* CONFIG_BPF_SYSCALL */
 
 #endif
diff --git a/kernel/bpf/net_namespace.c b/kernel/bpf/net_namespace.c
index 78cf061f8179..b951dab2687f 100644
--- a/kernel/bpf/net_namespace.c
+++ b/kernel/bpf/net_namespace.c
@@ -189,6 +189,7 @@ int netns_bpf_prog_query(const union bpf_attr *attr,
 int netns_bpf_prog_attach(const union bpf_attr *attr, struct bpf_prog *prog)
 {
 	enum netns_bpf_attach_type type;
+	struct bpf_prog *attached;
 	struct net *net;
 	int ret;
 
@@ -207,12 +208,26 @@ int netns_bpf_prog_attach(const union bpf_attr *attr, struct bpf_prog *prog)
 
 	switch (type) {
 	case NETNS_BPF_FLOW_DISSECTOR:
-		ret = flow_dissector_bpf_prog_attach(net, prog);
+		ret = flow_dissector_bpf_prog_attach_check(net, prog);
 		break;
 	default:
 		ret = -EINVAL;
 		break;
 	}
+	if (ret)
+		goto out_unlock;
+
+	attached = rcu_dereference_protected(net->bpf.progs[type],
+					     lockdep_is_held(&netns_bpf_mutex));
+	if (attached == prog) {
+		/* The same program cannot be attached twice */
+		ret = -EINVAL;
+		goto out_unlock;
+	}
+	rcu_assign_pointer(net->bpf.progs[type], prog);
+	if (attached)
+		bpf_prog_put(attached);
+
 out_unlock:
 	mutex_unlock(&netns_bpf_mutex);
 
@@ -277,7 +292,7 @@ static int netns_bpf_link_attach(struct net *net, struct bpf_link *link,
 
 	switch (type) {
 	case NETNS_BPF_FLOW_DISSECTOR:
-		err = flow_dissector_bpf_prog_attach(net, link->prog);
+		err = flow_dissector_bpf_prog_attach_check(net, link->prog);
 		break;
 	default:
 		err = -EINVAL;
@@ -286,6 +301,7 @@ static int netns_bpf_link_attach(struct net *net, struct bpf_link *link,
 	if (err)
 		goto out_unlock;
 
+	rcu_assign_pointer(net->bpf.progs[type], link->prog);
 	net->bpf.links[type] = link;
 
 out_unlock:
diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index d02df0b6d0d9..b57fb1359395 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -70,10 +70,10 @@ void skb_flow_dissector_init(struct flow_dissector *flow_dissector,
 EXPORT_SYMBOL(skb_flow_dissector_init);
 
 #ifdef CONFIG_BPF_SYSCALL
-int flow_dissector_bpf_prog_attach(struct net *net, struct bpf_prog *prog)
+int flow_dissector_bpf_prog_attach_check(struct net *net,
+					 struct bpf_prog *prog)
 {
 	enum netns_bpf_attach_type type = NETNS_BPF_FLOW_DISSECTOR;
-	struct bpf_prog *attached;
 
 	if (net == &init_net) {
 		/* BPF flow dissector in the root namespace overrides
@@ -97,15 +97,6 @@ int flow_dissector_bpf_prog_attach(struct net *net, struct bpf_prog *prog)
 			return -EEXIST;
 	}
 
-	attached = rcu_dereference_protected(net->bpf.progs[type],
-					     lockdep_is_held(&netns_bpf_mutex));
-	if (attached == prog)
-		/* The same program cannot be attached twice */
-		return -EINVAL;
-
-	rcu_assign_pointer(net->bpf.progs[type], prog);
-	if (attached)
-		bpf_prog_put(attached);
 	return 0;
 }
 #endif /* CONFIG_BPF_SYSCALL */
-- 
2.25.4