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

From:   Yonghong Song <redacted>
Date:   Thu, 29 Jul 2021 23:24:41 -0700

On 7/29/21 4:36 PM, Kuniyuki Iwashima wrote:

quoted

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.

quoted

Signed-off-by: Kuniyuki Iwashima <redacted>
---
  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.

Thanks for your review!
I will implement the extra call in the next spin.

Just out of curiosity, is there a specific use case for the last call?