Re: [PATCH bpf-next 5/7] bpf: enable bpf cgroup hooks to retrieve cgroup v2 and ancestor id

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Fri, Mar 27, 2020 at 8:59 AM Daniel Borkmann <daniel@iogearbox.net> wrote:
>
> 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>
> ---

Same question about just directly getting this from current through CO-RE.

>  include/linux/bpf.h            |  1 +
>  include/uapi/linux/bpf.h       | 21 ++++++++++++++++++++-
>  kernel/bpf/core.c              |  1 +
>  kernel/bpf/helpers.c           | 18 ++++++++++++++++++
>  net/core/filter.c              | 12 ++++++++++++
>  tools/include/uapi/linux/bpf.h | 21 ++++++++++++++++++++-
>  6 files changed, 72 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 78046c570596..372708eeaecd 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1501,6 +1501,7 @@ extern const struct bpf_func_proto bpf_get_stack_proto;
>  extern const struct bpf_func_proto bpf_sock_map_update_proto;
>  extern const struct bpf_func_proto bpf_sock_hash_update_proto;
>  extern const struct bpf_func_proto bpf_get_current_cgroup_id_proto;
> +extern const struct bpf_func_proto bpf_get_current_ancestor_cgroup_id_proto;
>  extern const struct bpf_func_proto bpf_msg_redirect_hash_proto;
>  extern const struct bpf_func_proto bpf_msg_redirect_map_proto;
>  extern const struct bpf_func_proto bpf_sk_redirect_hash_proto;
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index bd81c4555206..222ba11966e3 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -2963,6 +2963,24 @@ union bpf_attr {
>   *             instead of sockets.
>   *     Return
>   *             A 8-byte long opaque number.
> + *
> + * u64 bpf_get_current_ancestor_cgroup_id(int ancestor_level)
> + *     Description
> + *             Return id of cgroup v2 that is ancestor of the cgroup associated
> + *             with the current task 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 the current task, then return value will be the
> + *             same as that of **bpf_get_current_cgroup_id**\ ().
> + *
> + *             The helper is useful to implement policies based on cgroups
> + *             that are upper in hierarchy than immediate cgroup associated
> + *             with the current task.
> + *
> + *             The format of returned id and helper limitations are same as in
> + *             **bpf_get_current_cgroup_id**\ ().
> + *     Return
> + *             The id is returned or 0 in case the id could not be retrieved.
>   */
>  #define __BPF_FUNC_MAPPER(FN)          \
>         FN(unspec),                     \
> @@ -3087,7 +3105,8 @@ union bpf_attr {
>         FN(read_branch_records),        \
>         FN(get_ns_current_pid_tgid),    \
>         FN(xdp_output),                 \
> -       FN(get_netns_cookie),
> +       FN(get_netns_cookie),           \
> +       FN(get_current_ancestor_cgroup_id),
>
>  /* integer value in 'imm' field of BPF_CALL instruction selects which helper
>   * function eBPF program intends to call
> 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]);
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 3083c7746ee0..5cec3ac9e3dd 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -6018,6 +6018,12 @@ sock_filter_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>                 return &bpf_get_netns_cookie_sock_proto;
>         case BPF_FUNC_perf_event_output:
>                 return &bpf_event_output_data_proto;
> +#ifdef CONFIG_CGROUPS
> +       case BPF_FUNC_get_current_cgroup_id:
> +               return &bpf_get_current_cgroup_id_proto;
> +       case BPF_FUNC_get_current_ancestor_cgroup_id:
> +               return &bpf_get_current_ancestor_cgroup_id_proto;
> +#endif
>  #ifdef CONFIG_CGROUP_NET_CLASSID
>         case BPF_FUNC_get_cgroup_classid:
>                 return &bpf_get_cgroup_classid_curr_proto;
> @@ -6052,6 +6058,12 @@ sock_addr_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>                 return &bpf_get_local_storage_proto;
>         case BPF_FUNC_perf_event_output:
>                 return &bpf_event_output_data_proto;
> +#ifdef CONFIG_CGROUPS
> +       case BPF_FUNC_get_current_cgroup_id:
> +               return &bpf_get_current_cgroup_id_proto;
> +       case BPF_FUNC_get_current_ancestor_cgroup_id:
> +               return &bpf_get_current_ancestor_cgroup_id_proto;
> +#endif
>  #ifdef CONFIG_CGROUP_NET_CLASSID
>         case BPF_FUNC_get_cgroup_classid:
>                 return &bpf_get_cgroup_classid_curr_proto;
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index bd81c4555206..222ba11966e3 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -2963,6 +2963,24 @@ union bpf_attr {
>   *             instead of sockets.
>   *     Return
>   *             A 8-byte long opaque number.
> + *
> + * u64 bpf_get_current_ancestor_cgroup_id(int ancestor_level)
> + *     Description
> + *             Return id of cgroup v2 that is ancestor of the cgroup associated
> + *             with the current task 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 the current task, then return value will be the
> + *             same as that of **bpf_get_current_cgroup_id**\ ().
> + *
> + *             The helper is useful to implement policies based on cgroups
> + *             that are upper in hierarchy than immediate cgroup associated
> + *             with the current task.
> + *
> + *             The format of returned id and helper limitations are same as in
> + *             **bpf_get_current_cgroup_id**\ ().
> + *     Return
> + *             The id is returned or 0 in case the id could not be retrieved.
>   */
>  #define __BPF_FUNC_MAPPER(FN)          \
>         FN(unspec),                     \
> @@ -3087,7 +3105,8 @@ union bpf_attr {
>         FN(read_branch_records),        \
>         FN(get_ns_current_pid_tgid),    \
>         FN(xdp_output),                 \
> -       FN(get_netns_cookie),
> +       FN(get_netns_cookie),           \
> +       FN(get_current_ancestor_cgroup_id),
>
>  /* integer value in 'imm' field of BPF_CALL instruction selects which helper
>   * function eBPF program intends to call
> --
> 2.21.0
>