[Devel] [PATCH RH8 3/5] unix: Show number of pending scm files of receive queue in fdinfo

[Vasily Averin]

Unix sockets like a block box. You never know what is stored there:
there may be a file descriptor holding a mount or a block device,
or there may be whole universes with namespaces, sockets with receive
queues full of sockets etc.

The patch adds a little debug and accounts number of files (not recursive),
which is in receive queue of a unix socket. Sometimes this is useful
to determine, that socket should be investigated or which task should
be killed to put reference counter on a resourse.

v2: Pass correct argument to lockdep

Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
(cherry picked from commit 3c32da19a858fb1ae8a76bf899160be49f338506)
VvS: taken from vz7 commit 56a318575ebf8cef4b677f9e20b9590848fcff85
Signed-off-by: Vasily Averin <vvs at virtuozzo.com>
---
 include/net/af_unix.h |  9 ++++++--
 net/unix/af_unix.c    | 54 +++++++++++++++++++++++++++++++++++++++----
 2 files changed, 57 insertions(+), 6 deletions(-)

diff --git a/include/net/af_unix.h b/include/net/af_unix.h
index 7ec1cdb66be8..a10e2c52bf9b 100644
--- a/include/net/af_unix.h
+++ b/include/net/af_unix.h
@@ -41,7 +41,11 @@ struct unix_skb_parms {
 	u32			consumed;
 } __randomize_layout;
 
-#define UNIXCB(skb) 	(*(struct unix_skb_parms *)&((skb)->cb))
+struct scm_stat {
+	u32 nr_fds;
+};
+
+#define UNIXCB(skb)	(*(struct unix_skb_parms *)&((skb)->cb))
 
 #define unix_state_lock(s)	spin_lock(&unix_sk(s)->lock)
 #define unix_state_unlock(s)	spin_unlock(&unix_sk(s)->lock)
@@ -64,7 +68,8 @@ struct unix_sock {
 #define UNIX_GC_CANDIDATE	0
 #define UNIX_GC_MAYBE_CYCLE	1
 	struct socket_wq	peer_wq;
-	wait_queue_entry_t		peer_wake;
+	wait_queue_entry_t	peer_wake;
+	struct scm_stat		scm_stat;
 };
 
 static inline struct unix_sock *unix_sk(const struct sock *sk)
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 5d47d67901af..67648b61ce11 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -673,6 +673,16 @@ static int unix_set_peek_off(struct sock *sk, int val)
 	return 0;
 }
 
+static void unix_show_fdinfo(struct seq_file *m, struct socket *sock)
+{
+	struct sock *sk = sock->sk;
+	struct unix_sock *u;
+
+	if (sk) {
+		u = unix_sk(sock->sk);
+		seq_printf(m, "scm_fds: %u\n", READ_ONCE(u->scm_stat.nr_fds));
+	}
+}
 
 static const struct proto_ops unix_stream_ops = {
 	.family =	PF_UNIX,
@@ -695,6 +705,7 @@ static const struct proto_ops unix_stream_ops = {
 	.sendpage =	unix_stream_sendpage,
 	.splice_read =	unix_stream_splice_read,
 	.set_peek_off =	unix_set_peek_off,
+	.show_fdinfo =	unix_show_fdinfo,
 };
 
 static const struct proto_ops unix_dgram_ops = {
@@ -717,6 +728,7 @@ static const struct proto_ops unix_dgram_ops = {
 	.mmap =		sock_no_mmap,
 	.sendpage =	sock_no_sendpage,
 	.set_peek_off =	unix_set_peek_off,
+	.show_fdinfo =	unix_show_fdinfo,
 };
 
 static const struct proto_ops unix_seqpacket_ops = {
@@ -739,6 +751,7 @@ static const struct proto_ops unix_seqpacket_ops = {
 	.mmap =		sock_no_mmap,
 	.sendpage =	sock_no_sendpage,
 	.set_peek_off =	unix_set_peek_off,
+	.show_fdinfo =	unix_show_fdinfo,
 };
 
 static struct proto unix_proto = {
@@ -776,6 +789,7 @@ static struct sock *unix_create1(struct net *net, struct socket *sock, int kern)
 	mutex_init(&u->bindlock); /* single task binding lock */
 	init_waitqueue_head(&u->peer_wait);
 	init_waitqueue_func_entry(&u->peer_wake, unix_dgram_peer_wake_relay);
+	memset(&u->scm_stat, 0, sizeof(struct scm_stat));
 	unix_insert_socket(unix_sockets_unbound(sk), sk);
 out:
 	if (sk == NULL)
@@ -1550,6 +1564,28 @@ static bool unix_skb_scm_eq(struct sk_buff *skb,
 	       unix_secdata_eq(scm, skb);
 }
 
+static void scm_stat_add(struct sock *sk, struct sk_buff *skb)
+{
+	struct scm_fp_list *fp = UNIXCB(skb).fp;
+	struct unix_sock *u = unix_sk(sk);
+
+	lockdep_assert_held(&sk->sk_receive_queue.lock);
+
+	if (unlikely(fp && fp->count))
+		u->scm_stat.nr_fds += fp->count;
+}
+
+static void scm_stat_del(struct sock *sk, struct sk_buff *skb)
+{
+	struct scm_fp_list *fp = UNIXCB(skb).fp;
+	struct unix_sock *u = unix_sk(sk);
+
+	lockdep_assert_held(&sk->sk_receive_queue.lock);
+
+	if (unlikely(fp && fp->count))
+		u->scm_stat.nr_fds -= fp->count;
+}
+
 /*
  *	Send AF_UNIX data.
  */
@@ -1735,7 +1771,10 @@ static int unix_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
 	if (sock_flag(other, SOCK_RCVTSTAMP))
 		__net_timestamp(skb);
 	maybe_add_creds(skb, sock, other);
-	skb_queue_tail(&other->sk_receive_queue, skb);
+	spin_lock(&other->sk_receive_queue.lock);
+	scm_stat_add(other, skb);
+	__skb_queue_tail(&other->sk_receive_queue, skb);
+	spin_unlock(&other->sk_receive_queue.lock);
 	unix_state_unlock(other);
 	other->sk_data_ready(other);
 	sock_put(other);
@@ -1837,7 +1876,10 @@ static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg,
 			goto pipe_err_free;
 
 		maybe_add_creds(skb, sock, other);
-		skb_queue_tail(&other->sk_receive_queue, skb);
+		spin_lock(&other->sk_receive_queue.lock);
+		scm_stat_add(other, skb);
+		__skb_queue_tail(&other->sk_receive_queue, skb);
+		spin_unlock(&other->sk_receive_queue.lock);
 		unix_state_unlock(other);
 		other->sk_data_ready(other);
 		sent += size;
@@ -2037,7 +2079,7 @@ static int unix_dgram_recvmsg(struct socket *sock, struct msghdr *msg,
 
 		skip = sk_peek_offset(sk, flags);
 		skb = __skb_try_recv_datagram(sk, &sk->sk_receive_queue, flags,
-					      NULL, &skip, &err, &last);
+					      scm_stat_del, &skip, &err, &last);
 		if (skb)
 			break;
 
@@ -2332,8 +2374,12 @@ static int unix_stream_read_generic(struct unix_stream_read_state *state,
 
 			sk_peek_offset_bwd(sk, chunk);
 
-			if (UNIXCB(skb).fp)
+			if (UNIXCB(skb).fp) {
+				spin_lock(&sk->sk_receive_queue.lock);
+				scm_stat_del(sk, skb);
+				spin_unlock(&sk->sk_receive_queue.lock);
 				unix_detach_fds(&scm, skb);
+			}
 
 			if (unix_skb_len(skb))
 				break;
-- 
2.25.1