bpf: add bpf_skb_cgroup_id helper

Add a new bpf_skb_cgroup_id() helper that allows to retrieve the
cgroup id from the skb's socket. This is useful in particular to
enable bpf_get_cgroup_classid()-like behavior for cgroup v1 in
cgroup v2 by allowing ID based matching on egress. This can in
particular be used in combination with applying policy e.g. from
map lookups, and also complements the older bpf_skb_under_cgroup()
interface. In user space the cgroup id for a given path can be
retrieved through the f_handle as demonstrated in [0] recently.

  [0] https://lkml.org/lkml/2018/5/22/1190

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 18 insertions, 1 deletions

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 64ac0f7a689e..661318141f72 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -2054,6 +2054,22 @@ union bpf_attr {
  *
  *      Return
  *              0
+ *
+ * uint64_t bpf_skb_cgroup_id(struct sk_buff *skb)
+ *      Description
+ *              Return the cgroup v2 id of the socket associated with the *skb*.
+ *              This is roughly similar to the **bpf_get_cgroup_classid**\ ()
+ *              helper for cgroup v1 by providing a tag resp. identifier that
+ *              can be matched on or used for map lookups e.g. to implement
+ *              policy. The cgroup v2 id of a given path in the hierarchy is
+ *              exposed in user space through the f_handle API in order to get
+ *              to the same 64-bit id.
+ *
+ *              This helper can be used on TC egress path, but not on ingress,
+ *              and 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.
  */
 #define __BPF_FUNC_MAPPER(FN)           \
         FN(unspec),                     \
@@ -2134,7 +2150,8 @@ union bpf_attr {
         FN(lwt_seg6_adjust_srh),        \
         FN(lwt_seg6_action),            \
         FN(rc_repeat),                  \
-        FN(rc_keydown),
+        FN(rc_keydown),                 \
+        FN(skb_cgroup_id),
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
  * function eBPF program intends to call