bpf: Introduce bpf_sk_{, ancestor_}cgroup_id helpers

With having ability to lookup sockets in cgroup skb programs it becomes
useful to access cgroup id of retrieved sockets so that policies can be
implemented based on origin cgroup of such socket.

For example, a container running in a cgroup can have cgroup skb ingress
program that can lookup peer socket that is sending packets to a process
inside the container and decide whether those packets should be allowed
or denied based on cgroup id of the peer.

More specifically such ingress program can implement intra-host policy
"allow incoming packets only from this same container and not from any
other container on same host" w/o relying on source IP addresses since
quite often it can be the case that containers share same IP address on
the host.

Introduce two new helpers for this use-case: bpf_sk_cgroup_id() and
bpf_sk_ancestor_cgroup_id().

These helpers are similar to existing bpf_skb_{,ancestor_}cgroup_id
helpers with the only difference that sk is used to get cgroup id
instead of skb, and share code with them.

See documentation in UAPI for more details.

Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/f5884981249ce911f63e9b57ecd5d7d19154ff39.1589486450.git.rdna@fb.com

1 files changed, 35 insertions, 1 deletions

diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 85cfdffde182..146c742f1d49 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -3121,6 +3121,38 @@ union bpf_attr {
  * 		0 on success, or a negative error in case of failure:
  *
  *		**-EOVERFLOW** if an overflow happened: The same object will be tried again.
+ *
+ * u64 bpf_sk_cgroup_id(struct bpf_sock *sk)
+ *	Description
+ *		Return the cgroup v2 id of the socket *sk*.
+ *
+ *		*sk* must be a non-**NULL** pointer to a full socket, e.g. one
+ *		returned from **bpf_sk_lookup_xxx**\ (),
+ *		**bpf_sk_fullsock**\ (), etc. The format of returned id is
+ *		same as in **bpf_skb_cgroup_id**\ ().
+ *
+ *		This helper is available only if the kernel was compiled with
+ *		the **CONFIG_SOCK_CGROUP_DATA** configuration option.
+ *	Return
+ *		The id is returned or 0 in case the id could not be retrieved.
+ *
+ * u64 bpf_sk_ancestor_cgroup_id(struct bpf_sock *sk, int ancestor_level)
+ *	Description
+ *		Return id of cgroup v2 that is ancestor of cgroup associated
+ *		with the *sk* at the *ancestor_level*.  The root cgroup is at
+ *		*ancestor_level* zero and each step down the hierarchy
+ *		increments the level. If *ancestor_level* == level of cgroup
+ *		associated with *sk*, then return value will be same as that
+ *		of **bpf_sk_cgroup_id**\ ().
+ *
+ *		The helper is useful to implement policies based on cgroups
+ *		that are upper in hierarchy than immediate cgroup associated
+ *		with *sk*.
+ *
+ *		The format of returned id and helper limitations are same as in
+ *		**bpf_sk_cgroup_id**\ ().
+ *	Return
+ *		The id is returned or 0 in case the id could not be retrieved.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -3250,7 +3282,9 @@ union bpf_attr {
 	FN(sk_assign),			\
 	FN(ktime_get_boot_ns),		\
 	FN(seq_printf),			\
-	FN(seq_write),
+	FN(seq_write),			\
+	FN(sk_cgroup_id),		\
+	FN(sk_ancestor_cgroup_id),
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
  * function eBPF program intends to call