bpf: Enable bpf cgroup hooks to retrieve cgroup v2 and ancestor id

Enable the bpf_get_current_cgroup_id() helper for connect(), sendmsg(),
recvmsg() and bind-related hooks in order to retrieve the cgroup v2
context which can then be used as part of the key for BPF map lookups,
for example. Given these hooks operate in process context 'current' is
always valid and pointing to the app that is performing mentioned
syscalls if it's subject to a v2 cgroup. Also with same motivation of
commit 7723628101aa ("bpf: Introduce bpf_skb_ancestor_cgroup_id helper")
enable retrieval of ancestor from current so the cgroup id can be used
for policy lookups which can then forbid connect() / bind(), for example.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/d2a7ef42530ad299e3cbb245e6c12374b72145ef.1585323121.git.daniel@iogearbox.net

2 files changed, 19 insertions, 0 deletions

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 914f3463aa41..916f5132a984 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -2156,6 +2156,7 @@ const struct bpf_func_proto bpf_get_current_pid_tgid_proto __weak;
 const struct bpf_func_proto bpf_get_current_uid_gid_proto __weak;
 const struct bpf_func_proto bpf_get_current_comm_proto __weak;
 const struct bpf_func_proto bpf_get_current_cgroup_id_proto __weak;
+const struct bpf_func_proto bpf_get_current_ancestor_cgroup_id_proto __weak;
 const struct bpf_func_proto bpf_get_local_storage_proto __weak;
 const struct bpf_func_proto bpf_get_ns_current_pid_tgid_proto __weak;
 
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 01878db15eaf..bafc53ddd350 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -340,6 +340,24 @@ const struct bpf_func_proto bpf_get_current_cgroup_id_proto = {
 	.ret_type	= RET_INTEGER,
 };
 
+BPF_CALL_1(bpf_get_current_ancestor_cgroup_id, int, ancestor_level)
+{
+	struct cgroup *cgrp = task_dfl_cgroup(current);
+	struct cgroup *ancestor;
+
+	ancestor = cgroup_ancestor(cgrp, ancestor_level);
+	if (!ancestor)
+		return 0;
+	return cgroup_id(ancestor);
+}
+
+const struct bpf_func_proto bpf_get_current_ancestor_cgroup_id_proto = {
+	.func		= bpf_get_current_ancestor_cgroup_id,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_ANYTHING,
+};
+
 #ifdef CONFIG_CGROUP_BPF
 DECLARE_PER_CPU(struct bpf_cgroup_storage*,
 		bpf_cgroup_storage[MAX_BPF_CGROUP_STORAGE_TYPE]);