Re: [PATCH bpf-next 1/2] bpf: af_unix: Implement BPF iterator for UNIX domain socket.

[Yonghong Song <yhs@fb.com>]

On 7/29/21 4:36 PM, Kuniyuki Iwashima wrote:
> This patch implements the BPF iterator for the UNIX domain socket.
> 
> Currently, the batch optimization introduced for the TCP iterator in the
> commit 04c7820b776f ("bpf: tcp: Bpf iter batching and lock_sock") is not
> applied.  It will require replacing the big lock for the hash table with
> small locks for each hash list not to block other processes.

Thanks for the contribution. The patch looks okay except
missing seq_ops->stop implementation, see below for more explanation.

> 
> Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
> ---
>   include/linux/btf_ids.h |  3 +-
>   net/unix/af_unix.c      | 78 +++++++++++++++++++++++++++++++++++++++++
>   2 files changed, 80 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/btf_ids.h b/include/linux/btf_ids.h
> index 57890b357f85..bed4b9964581 100644
> --- a/include/linux/btf_ids.h
> +++ b/include/linux/btf_ids.h
> @@ -172,7 +172,8 @@ extern struct btf_id_set name;
>   	BTF_SOCK_TYPE(BTF_SOCK_TYPE_TCP_TW, tcp_timewait_sock)		\
>   	BTF_SOCK_TYPE(BTF_SOCK_TYPE_TCP6, tcp6_sock)			\
>   	BTF_SOCK_TYPE(BTF_SOCK_TYPE_UDP, udp_sock)			\
> -	BTF_SOCK_TYPE(BTF_SOCK_TYPE_UDP6, udp6_sock)
> +	BTF_SOCK_TYPE(BTF_SOCK_TYPE_UDP6, udp6_sock)			\
> +	BTF_SOCK_TYPE(BTF_SOCK_TYPE_UNIX, unix_sock)
>   
>   enum {
>   #define BTF_SOCK_TYPE(name, str) name,
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 89927678c0dc..d45ad87e3a49 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -113,6 +113,7 @@
>   #include <linux/security.h>
>   #include <linux/freezer.h>
>   #include <linux/file.h>
> +#include <linux/btf_ids.h>
>   
>   #include "scm.h"
>   
> @@ -2935,6 +2936,49 @@ static const struct seq_operations unix_seq_ops = {
>   	.stop   = unix_seq_stop,
>   	.show   = unix_seq_show,
>   };
> +
> +#ifdef CONFIG_BPF_SYSCALL
> +struct bpf_iter__unix {
> +	__bpf_md_ptr(struct bpf_iter_meta *, meta);
> +	__bpf_md_ptr(struct unix_sock *, unix_sk);
> +	uid_t uid __aligned(8);
> +};
> +
> +static int unix_prog_seq_show(struct bpf_prog *prog, struct bpf_iter_meta *meta,
> +			      struct unix_sock *unix_sk, uid_t uid)
> +{
> +	struct bpf_iter__unix ctx;
> +
> +	meta->seq_num--;  /* skip SEQ_START_TOKEN */
> +	ctx.meta = meta;
> +	ctx.unix_sk = unix_sk;
> +	ctx.uid = uid;
> +	return bpf_iter_run_prog(prog, &ctx);
> +}
> +
> +static int bpf_iter_unix_seq_show(struct seq_file *seq, void *v)
> +{
> +	struct bpf_iter_meta meta;
> +	struct bpf_prog *prog;
> +	struct sock *sk = v;
> +	uid_t uid;
> +
> +	if (v == SEQ_START_TOKEN)
> +		return 0;
> +
> +	uid = from_kuid_munged(seq_user_ns(seq), sock_i_uid(sk));
> +	meta.seq = seq;
> +	prog = bpf_iter_get_info(&meta, false);
> +	return unix_prog_seq_show(prog, &meta, v, uid);
> +}
> +
> +static const struct seq_operations bpf_iter_unix_seq_ops = {
> +	.start	= unix_seq_start,
> +	.next	= unix_seq_next,
> +	.stop	= unix_seq_stop,

Although it is not required for /proc/net/unix, we should still
implement bpf_iter version of seq_ops->stop here. The main purpose
of bpf_iter specific seq_ops->stop is to call bpf program one
more time after ALL elements have been traversed. Such
functionality is implemented in all other bpf_iter variants.

> +	.show	= bpf_iter_unix_seq_show,
> +};
> +#endif
>   #endif
>   
>   static const struct net_proto_family unix_family_ops = {
> @@ -2975,6 +3019,35 @@ static struct pernet_operations unix_net_ops = {
>   	.exit = unix_net_exit,
>   };
>   
[...]