unix: Show number of pending scm files of receive queue in fdinfo

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@virtuozzo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/af_unix.h b/include/net/af_unix.h
index 3426d6d..17e10fb 100644 (file)
--- a/include/net/af_unix.h
+++ b/include/net/af_unix.h
@@ -41,6 +41,10 @@ struct unix_skb_parms {
        u32                     consumed;
 } __randomize_layout;
 
+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)
@@ -65,6 +69,7 @@ struct unix_sock {
 #define UNIX_GC_MAYBE_CYCLE    1
        struct socket_wq        peer_wq;
        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 7cfdce1..050eed3 100644 (file)
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -676,6 +676,16 @@ 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,
@@ -701,6 +711,7 @@ 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 = {
@@ -726,6 +737,7 @@ 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 = {
@@ -751,6 +763,7 @@ 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 = {
@@ -788,6 +801,7 @@ 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)
@@ -1572,6 +1586,28 @@ 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.
  */
@@ -1757,7 +1793,10 @@ restart_locked:
        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);
@@ -1859,7 +1898,10 @@ 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;
@@ -2058,8 +2100,8 @@ static int unix_dgram_recvmsg(struct socket *sock, struct msghdr *msg,
                mutex_lock(&u->iolock);
 
                skip = sk_peek_offset(sk, flags);
-               skb = __skb_try_recv_datagram(sk, flags, NULL, &skip, &err,
-                                             &last);
+               skb = __skb_try_recv_datagram(sk, flags, scm_stat_del,
+                                             &skip, &err, &last);
                if (skb)
                        break;
 
@@ -2353,8 +2395,12 @@ unlock:
 
                        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;