netdev - [PATCH bpf-next v4 1/2] bpf: support BPF_PROG_QUERY for BPF_FLOW_DISSECTOR attach

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Message-Id: <20190424213141.201134-1-sdf@google.com>
Date:   Wed, 24 Apr 2019 14:31:40 -0700
From:   Stanislav Fomichev <sdf@...gle.com>
To:     netdev@...r.kernel.org, bpf@...r.kernel.org
Cc:     davem@...emloft.net, ast@...nel.org, daniel@...earbox.net,
        jakub.kicinski@...ronome.com, quentin.monnet@...ronome.com,
        Stanislav Fomichev <sdf@...gle.com>,
        Jann Horn <jannh@...gle.com>
Subject: [PATCH bpf-next v4 1/2] bpf: support BPF_PROG_QUERY for
 BPF_FLOW_DISSECTOR attach_type

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

v4:
* add missing put_net (Jann Horn)

v3:
* add missing inline to skb_flow_dissector_prog_query static def
  (kbuild test robot <lkp@...el.com>)

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

Cc: Jann Horn <jannh@...gle.com>
Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
---
 include/linux/skbuff.h    |  8 +++++++
 kernel/bpf/syscall.c      |  2 ++
 net/core/flow_dissector.c | 46 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 56 insertions(+)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 998256c2820b..6d58fa8a65fd 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 inline 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..27466e54ad3a 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -65,6 +65,52 @@ 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;
+	int ret = 0;
+
+	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))) {
+		ret = -EFAULT;
+		goto out;
+	}
+	if (copy_to_user(&uattr->query.prog_cnt, &prog_cnt, sizeof(prog_cnt))) {
+		ret = -EFAULT;
+		goto out;
+	}
+
+	if (!attr->query.prog_cnt || !prog_ids || !prog_cnt)
+		goto out;
+
+	if (copy_to_user(prog_ids, &prog_id, sizeof(u32))) {
+		ret = -EFAULT;
+		goto out;
+	}
+
+out:
+	put_net(net);
+	return ret;
+}
+
 int skb_flow_dissector_bpf_prog_attach(const union bpf_attr *attr,
 				       struct bpf_prog *prog)
 {
-- 
2.21.0.593.g511ec345e18-goog