Re: [Patch net-next v3] sock_map: dump socket map id via diag

[Stanislav Fomichev <sdf@google.com>]

On Sun, Mar 19, 2023 at 12:19 PM Cong Wang <xiyou.wangcong@gmail.com> wrote:
>
> From: Cong Wang <cong.wang@bytedance.com>
>
> Currently there is no way to know which sockmap a socket has been added
> to from outside, especially for that a socket can be added to multiple
> sockmap's. We could dump this via socket diag, as shown below.
>
> Sample output:
>
>   # ./iproute2/misc/ss -tnaie --bpf-map
>   ESTAB  0      344329     127.0.0.1:1234     127.0.0.1:40912 ino:21098 sk:5 cgroup:/user.slice/user-0.slice/session-c1.scope <-> sockmap: 1
>
>   # bpftool map
>   1: sockmap  flags 0x0
>         key 4B  value 4B  max_entries 2  memlock 4096B
>         pids echo-sockmap(549)
>   4: array  name pid_iter.rodata  flags 0x480
>         key 4B  value 4B  max_entries 1  memlock 4096B
>         btf_id 10  frozen
>         pids bpftool(624)
>
> In the future, we could dump other sockmap related stats too, hence I
> make it a nested attribute.
>
> Cc: John Fastabend <john.fastabend@gmail.com>
> Cc: Jakub Sitnicki <jakub@cloudflare.com>
> Signed-off-by: Cong Wang <cong.wang@bytedance.com>

Looks fine from my POW, will let others comment.

One thing I still don't understand here: what is missing from the
socket iterators to implement this? Is it all the sk_psock_get magic?
I remember you dismissed Yonghong's suggestion on v1, but have you
actually tried it?

Also: a test would be nice to have. I know you've tested it with the
iproute2, but having something regularly exercised by the ci seems
good to have (and not a ton of work).

> ---
> v3: remove redundant rcu read lock
>     use likely() for psock check
>
> v2: rename enum's with more generic names
>     sock_map_idiag_dump -> sock_map_diag_dump()
>     make sock_map_diag_dump() return number of maps
>
>  include/linux/bpf.h            |  1 +
>  include/uapi/linux/inet_diag.h |  1 +
>  include/uapi/linux/sock_diag.h |  8 ++++++
>  include/uapi/linux/unix_diag.h |  1 +
>  net/core/sock_map.c            | 46 ++++++++++++++++++++++++++++++++++
>  net/ipv4/inet_diag.c           |  5 ++++
>  net/unix/diag.c                |  6 +++++
>  7 files changed, 68 insertions(+)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 6792a7940e1e..4cc315ce26a9 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -2638,6 +2638,7 @@ int sock_map_bpf_prog_query(const union bpf_attr *attr,
>  void sock_map_unhash(struct sock *sk);
>  void sock_map_destroy(struct sock *sk);
>  void sock_map_close(struct sock *sk, long timeout);
> +int sock_map_diag_dump(struct sock *sk, struct sk_buff *skb, int attr);
>  #else
>  static inline int bpf_dev_bound_kfunc_check(struct bpf_verifier_log *log,
>                                             struct bpf_prog_aux *prog_aux)
> diff --git a/include/uapi/linux/inet_diag.h b/include/uapi/linux/inet_diag.h
> index 50655de04c9b..d1f1e4522633 100644
> --- a/include/uapi/linux/inet_diag.h
> +++ b/include/uapi/linux/inet_diag.h
> @@ -161,6 +161,7 @@ enum {
>         INET_DIAG_SK_BPF_STORAGES,
>         INET_DIAG_CGROUP_ID,
>         INET_DIAG_SOCKOPT,
> +       INET_DIAG_BPF_MAP,
>         __INET_DIAG_MAX,
>  };
>
> diff --git a/include/uapi/linux/sock_diag.h b/include/uapi/linux/sock_diag.h
> index 5f74a5f6091d..7c961940b408 100644
> --- a/include/uapi/linux/sock_diag.h
> +++ b/include/uapi/linux/sock_diag.h
> @@ -62,4 +62,12 @@ enum {
>
>  #define SK_DIAG_BPF_STORAGE_MAX        (__SK_DIAG_BPF_STORAGE_MAX - 1)
>
> +enum {
> +       SK_DIAG_BPF_MAP_NONE,
> +       SK_DIAG_BPF_MAP_IDS,
> +       __SK_DIAG_BPF_MAP_MAX,
> +};
> +
> +#define SK_DIAG_BPF_MAP_MAX        (__SK_DIAG_BPF_MAP_MAX - 1)
> +
>  #endif /* _UAPI__SOCK_DIAG_H__ */
> diff --git a/include/uapi/linux/unix_diag.h b/include/uapi/linux/unix_diag.h
> index a1988576fa8a..b95a2b33521d 100644
> --- a/include/uapi/linux/unix_diag.h
> +++ b/include/uapi/linux/unix_diag.h
> @@ -42,6 +42,7 @@ enum {
>         UNIX_DIAG_MEMINFO,
>         UNIX_DIAG_SHUTDOWN,
>         UNIX_DIAG_UID,
> +       UNIX_DIAG_BPF_MAP,
>
>         __UNIX_DIAG_MAX,
>  };
> diff --git a/net/core/sock_map.c b/net/core/sock_map.c
> index 9b854e236d23..c4049095f64e 100644
> --- a/net/core/sock_map.c
> +++ b/net/core/sock_map.c
> @@ -1656,6 +1656,52 @@ void sock_map_close(struct sock *sk, long timeout)
>  }
>  EXPORT_SYMBOL_GPL(sock_map_close);
>
> +int sock_map_diag_dump(struct sock *sk, struct sk_buff *skb, int attrtype)
> +{
> +       struct sk_psock_link *link;
> +       struct nlattr *nla, *attr;
> +       int nr_links = 0, ret = 0;
> +       struct sk_psock *psock;
> +       u32 *ids;
> +
> +       psock = sk_psock_get(sk);
> +       if (likely(!psock))
> +               return 0;
> +
> +       nla = nla_nest_start_noflag(skb, attrtype);
> +       if (!nla) {
> +               sk_psock_put(sk, psock);
> +               return -EMSGSIZE;
> +       }
> +       spin_lock_bh(&psock->link_lock);
> +       list_for_each_entry(link, &psock->link, list)
> +               nr_links++;
> +
> +       attr = nla_reserve(skb, SK_DIAG_BPF_MAP_IDS,
> +                          sizeof(link->map->id) * nr_links);
> +       if (!attr) {
> +               ret = -EMSGSIZE;
> +               goto unlock;
> +       }
> +
> +       ids = nla_data(attr);
> +       list_for_each_entry(link, &psock->link, list) {
> +               *ids = link->map->id;
> +               ids++;
> +       }
> +unlock:
> +       spin_unlock_bh(&psock->link_lock);
> +       sk_psock_put(sk, psock);
> +       if (ret) {
> +               nla_nest_cancel(skb, nla);
> +       } else {
> +               ret = nr_links;
> +               nla_nest_end(skb, nla);
> +       }
> +       return ret;
> +}
> +EXPORT_SYMBOL_GPL(sock_map_diag_dump);
> +
>  static int sock_map_iter_attach_target(struct bpf_prog *prog,
>                                        union bpf_iter_link_info *linfo,
>                                        struct bpf_iter_aux_info *aux)
> diff --git a/net/ipv4/inet_diag.c b/net/ipv4/inet_diag.c
> index b812eb36f0e3..0949909d5b46 100644
> --- a/net/ipv4/inet_diag.c
> +++ b/net/ipv4/inet_diag.c
> @@ -197,6 +197,11 @@ int inet_diag_msg_attrs_fill(struct sock *sk, struct sk_buff *skb,
>                     &inet_sockopt))
>                 goto errout;
>
> +#ifdef CONFIG_BPF_SYSCALL
> +       if (sock_map_diag_dump(sk, skb, INET_DIAG_BPF_MAP) < 0)
> +               goto errout;
> +#endif
> +
>         return 0;
>  errout:
>         return 1;
> diff --git a/net/unix/diag.c b/net/unix/diag.c
> index 616b55c5b890..54aa8da2831e 100644
> --- a/net/unix/diag.c
> +++ b/net/unix/diag.c
> @@ -6,6 +6,7 @@
>  #include <linux/skbuff.h>
>  #include <linux/module.h>
>  #include <linux/uidgid.h>
> +#include <linux/bpf.h>
>  #include <net/netlink.h>
>  #include <net/af_unix.h>
>  #include <net/tcp_states.h>
> @@ -172,6 +173,11 @@ static int sk_diag_fill(struct sock *sk, struct sk_buff *skb, struct unix_diag_r
>             sk_diag_dump_uid(sk, skb, user_ns))
>                 goto out_nlmsg_trim;
>
> +#ifdef CONFIG_BPF_SYSCALL
> +       if (sock_map_diag_dump(sk, skb, UNIX_DIAG_BPF_MAP) < 0)
> +               goto out_nlmsg_trim;
> +#endif
> +
>         nlmsg_end(skb, nlh);
>         return 0;
>
> --
> 2.34.1
>