[PATCH bpf-next v2 1/2] bpf: support BPF_PROG_QUERY for BPF_FLOW_DISSECTOR attach_type

[Stanislav Fomichev]

target_fd is target namespace. If there is a flow dissector BPF program
attached to that namespace, its (single) id is returned.

v2:
* don't sleep in rcu critical section (Jakub Kicinski)
* check input prog_cnt (exit early)

Signed-off-by: Stanislav Fomichev <s...@google.com>
---
 include/linux/skbuff.h    |  8 ++++++++
 kernel/bpf/syscall.c      |  2 ++
 net/core/flow_dissector.c | 37 +++++++++++++++++++++++++++++++++++++
 3 files changed, 47 insertions(+)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 998256c2820b..9f499c0ac53b 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1258,11 +1258,19 @@ void skb_flow_dissector_init(struct flow_dissector 
*flow_dissector,
                             unsigned int key_count);
 
 #ifdef CONFIG_NET
+int skb_flow_dissector_prog_query(const union bpf_attr *attr,
+                                 union bpf_attr __user *uattr);
 int skb_flow_dissector_bpf_prog_attach(const union bpf_attr *attr,
                                       struct bpf_prog *prog);
 
 int skb_flow_dissector_bpf_prog_detach(const union bpf_attr *attr);
 #else
+static int skb_flow_dissector_prog_query(const union bpf_attr *attr,
+                                        union bpf_attr __user *uattr)
+{
+       return -EOPNOTSUPP;
+}
+
 static inline int skb_flow_dissector_bpf_prog_attach(const union bpf_attr 
*attr,
                                                     struct bpf_prog *prog)
 {
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 92c9b8a32b50..b0de49598341 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2009,6 +2009,8 @@ static int bpf_prog_query(const union bpf_attr *attr,
                break;
        case BPF_LIRC_MODE2:
                return lirc_prog_query(attr, uattr);
+       case BPF_FLOW_DISSECTOR:
+               return skb_flow_dissector_prog_query(attr, uattr);
        default:
                return -EINVAL;
        }
diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index fac712cee9d5..12b92c7d1eae 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -65,6 +65,43 @@ void skb_flow_dissector_init(struct flow_dissector 
*flow_dissector,
 }
 EXPORT_SYMBOL(skb_flow_dissector_init);
 
+int skb_flow_dissector_prog_query(const union bpf_attr *attr,
+                                 union bpf_attr __user *uattr)
+{
+       __u32 __user *prog_ids = u64_to_user_ptr(attr->query.prog_ids);
+       u32 prog_id, prog_cnt = 0, flags = 0;
+       struct bpf_prog *attached;
+       struct net *net;
+
+       if (attr->query.query_flags)
+               return -EINVAL;
+
+       net = get_net_ns_by_fd(attr->query.target_fd);
+       if (IS_ERR(net))
+               return PTR_ERR(net);
+
+       rcu_read_lock();
+       attached = rcu_dereference(net->flow_dissector_prog);
+       if (attached) {
+               prog_cnt = 1;
+               prog_id = attached->aux->id;
+       }
+       rcu_read_unlock();
+
+       if (copy_to_user(&uattr->query.attach_flags, &flags, sizeof(flags)))
+               return -EFAULT;
+       if (copy_to_user(&uattr->query.prog_cnt, &prog_cnt, sizeof(prog_cnt)))
+               return -EFAULT;
+
+       if (!attr->query.prog_cnt || !prog_ids || !prog_cnt)
+               return 0;
+
+       if (copy_to_user(prog_ids, &prog_id, sizeof(u32)))
+               return -EFAULT;
+
+       return 0;
+}
+
 int skb_flow_dissector_bpf_prog_attach(const union bpf_attr *attr,
                                       struct bpf_prog *prog)
 {
-- 
2.21.0.593.g511ec345e18-goog