linux-kernel - [PATCH bpf-next v1 1/2] bpf: sock ops: add netns in bpf context

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Message-Id: <20190412100018.20852-1-alban@kinvolk.io>
Date:   Fri, 12 Apr 2019 12:00:17 +0200
From:   Alban Crequy <alban.crequy@...il.com>
To:     john.fastabend@...il.com, ast@...nel.org, daniel@...earbox.net
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, alban@...volk.io, iago@...volk.io
Subject: [PATCH bpf-next v1 1/2] bpf: sock ops: add netns in bpf context

From: Alban Crequy <alban@...volk.io>

sockops programs can now access the network namespace inode via
(struct bpf_sock_ops)->netns. This can be useful to apply different
policies on different network namespaces.

In the unlikely case where network namespaces are not compiled in
(CONFIG_NET_NS=n), the verifier will not allow access to ->netns.

Signed-off-by: Alban Crequy <alban@...volk.io>
---
 include/uapi/linux/bpf.h |  1 +
 net/core/filter.c        | 40 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 31a27dd337dc..5afaab25f205 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -3069,6 +3069,7 @@ struct bpf_sock_ops {
 	__u32 sk_txhash;
 	__u64 bytes_received;
 	__u64 bytes_acked;
+	__u64 netns;
 };
 
 /* Definitions for bpf_sock_ops_cb_flags */
diff --git a/net/core/filter.c b/net/core/filter.c
index 22eb2edf5573..f5e75b6fecb2 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -6758,6 +6758,14 @@ static bool sock_ops_is_valid_access(int off, int size,
 		}
 	} else {
 		switch (off) {
+		case offsetof(struct bpf_sock_ops, netns):
+#ifdef CONFIG_NET_NS
+			if (size != sizeof(__u64))
+				return false;
+#else
+			return false;
+#endif
+			break;
 		case bpf_ctx_range_till(struct bpf_sock_ops, bytes_received,
 					bytes_acked):
 			if (size != sizeof(__u64))
@@ -7908,6 +7916,38 @@ static u32 sock_ops_convert_ctx_access(enum bpf_access_type type,
 		SOCK_OPS_GET_OR_SET_FIELD(sk_txhash, sk_txhash,
 					  struct sock, type);
 		break;
+
+	case offsetof(struct bpf_sock_ops, netns):
+#ifdef CONFIG_NET_NS
+		/* Loading: sk_ops->sk->__sk_common.skc_net.net->ns.inum
+		 * Type: (struct bpf_sock_ops_kern *)
+		 *       ->(struct sock *)
+		 *       ->(struct sock_common)
+		 *       .possible_net_t
+		 *       .(struct net *)
+		 *       ->(struct ns_common)
+		 *       .(unsigned int)
+		 */
+		BUILD_BUG_ON(offsetof(struct sock, __sk_common) != 0);
+		BUILD_BUG_ON(offsetof(possible_net_t, net) != 0);
+		*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(
+						struct bpf_sock_ops_kern, sk),
+				      si->dst_reg, si->src_reg,
+				      offsetof(struct bpf_sock_ops_kern, sk));
+		*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(
+						possible_net_t, net),
+				      si->dst_reg, si->dst_reg,
+				      offsetof(struct sock_common, skc_net));
+		*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(
+						struct ns_common, inum),
+				      si->dst_reg, si->dst_reg,
+				      offsetof(struct net, ns) +
+				      offsetof(struct ns_common, inum));
+#else
+		*insn++ = BPF_MOV64_IMM(si->dst_reg, 0);
+#endif
+		break;
+
 	}
 	return insn - insn_buf;
 }
-- 
2.20.1