Revert "net/sctp: fix race condition in sctp_destroy_sock"

This reverts commit b166a20b07382b8bc1dcee2a448715c9c2c81b5b.

This one has to be reverted as it introduced a dead lock, as
syzbot reported:

       CPU0                    CPU1
       ----                    ----
  lock(&net->sctp.addr_wq_lock);
                               lock(slock-AF_INET6);
                               lock(&net->sctp.addr_wq_lock);
  lock(slock-AF_INET6);

CPU0 is the thread of sctp_addr_wq_timeout_handler(), and CPU1
is that of sctp_close().

The original issue this commit fixed will be fixed in the next
patch.

Reported-by: syzbot+959223586843e69a2674@syzkaller.appspotmail.com
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index b7b9013..76a388b 100644 (file)
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -1520,9 +1520,11 @@ static void sctp_close(struct sock *sk, long timeout)
 
        /* Supposedly, no process has access to the socket, but
         * the net layers still may.
+        * Also, sctp_destroy_sock() needs to be called with addr_wq_lock
+        * held and that should be grabbed before socket lock.
         */
-       local_bh_disable();
-       bh_lock_sock(sk);
+       spin_lock_bh(&net->sctp.addr_wq_lock);
+       bh_lock_sock_nested(sk);
 
        /* Hold the sock, since sk_common_release() will put sock_put()
         * and we have just a little more cleanup.
@@ -1531,7 +1533,7 @@ static void sctp_close(struct sock *sk, long timeout)
        sk_common_release(sk);
 
        bh_unlock_sock(sk);
-       local_bh_enable();
+       spin_unlock_bh(&net->sctp.addr_wq_lock);
 
        sock_put(sk);
 
@@ -4991,6 +4993,9 @@ static int sctp_init_sock(struct sock *sk)
        sk_sockets_allocated_inc(sk);
        sock_prot_inuse_add(net, sk->sk_prot, 1);
 
+       /* Nothing can fail after this block, otherwise
+        * sctp_destroy_sock() will be called without addr_wq_lock held
+        */
        if (net->sctp.default_auto_asconf) {
                spin_lock(&sock_net(sk)->sctp.addr_wq_lock);
                list_add_tail(&sp->auto_asconf_list,
@@ -5025,9 +5030,7 @@ static void sctp_destroy_sock(struct sock *sk)
 
        if (sp->do_auto_asconf) {
                sp->do_auto_asconf = 0;
-               spin_lock_bh(&sock_net(sk)->sctp.addr_wq_lock);
                list_del(&sp->auto_asconf_list);
-               spin_unlock_bh(&sock_net(sk)->sctp.addr_wq_lock);
        }
        sctp_endpoint_free(sp->ep);
        local_bh_disable();