cgroup: bpf: Add bpf_skb_in_cgroup_proto

Adds a bpf helper, bpf_skb_in_cgroup, to decide if a skb->sk
belongs to a descendant of a cgroup2.  It is similar to the
feature added in netfilter:
commit c38c4597e4bf ("netfilter: implement xt_cgroup cgroup2 path match")

The user is expected to populate a BPF_MAP_TYPE_CGROUP_ARRAY
which will be used by the bpf_skb_in_cgroup.

Modifications to the bpf verifier is to ensure BPF_MAP_TYPE_CGROUP_ARRAY
and bpf_skb_in_cgroup() are always used together.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Cc: Alexei Starovoitov <ast@fb.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Tejun Heo <tj@kernel.org>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 38 insertions, 0 deletions

diff --git a/net/core/filter.c b/net/core/filter.c
index 76fee35da244..54071cf70fb5 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2239,6 +2239,40 @@ bpf_get_skb_set_tunnel_proto(enum bpf_func_id which)
         }
 }
 
+#ifdef CONFIG_SOCK_CGROUP_DATA
+static u64 bpf_skb_in_cgroup(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
+{
+        struct sk_buff *skb = (struct sk_buff *)(long)r1;
+        struct bpf_map *map = (struct bpf_map *)(long)r2;
+        struct bpf_array *array = container_of(map, struct bpf_array, map);
+        struct cgroup *cgrp;
+        struct sock *sk;
+        u32 i = (u32)r3;
+
+        sk = skb->sk;
+        if (!sk || !sk_fullsock(sk))
+                return -ENOENT;
+
+        if (unlikely(i >= array->map.max_entries))
+                return -E2BIG;
+
+        cgrp = READ_ONCE(array->ptrs[i]);
+        if (unlikely(!cgrp))
+                return -EAGAIN;
+
+        return cgroup_is_descendant(sock_cgroup_ptr(&sk->sk_cgrp_data), cgrp);
+}
+
+static const struct bpf_func_proto bpf_skb_in_cgroup_proto = {
+        .func           = bpf_skb_in_cgroup,
+        .gpl_only       = false,
+        .ret_type       = RET_INTEGER,
+        .arg1_type      = ARG_PTR_TO_CTX,
+        .arg2_type      = ARG_CONST_MAP_PTR,
+        .arg3_type      = ARG_ANYTHING,
+};
+#endif
+
 static const struct bpf_func_proto *
 sk_filter_func_proto(enum bpf_func_id func_id)
 {
@@ -2307,6 +2341,10 @@ tc_cls_act_func_proto(enum bpf_func_id func_id)
                 return bpf_get_event_output_proto();
         case BPF_FUNC_get_smp_processor_id:
                 return &bpf_get_smp_processor_id_proto;
+#ifdef CONFIG_SOCK_CGROUP_DATA
+        case BPF_FUNC_skb_in_cgroup:
+                return &bpf_skb_in_cgroup_proto;
+#endif
         default:
                 return sk_filter_func_proto(func_id);
         }