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Subject[PATCH bpf-next v1 1/2] bpf: sock ops: add netns in bpf context
Date
From: Alban Crequy <alban@kinvolk.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@kinvolk.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
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