llc: delete timers synchronously in llc_sk_free()

The connection timers of an llc sock could be still flying
after we delete them in llc_sk_free(), and even possibly
after we free the sock. We could just wait synchronously
here in case of troubles.

Note, I leave other call paths as they are, since they may
not have to wait, at least we can change them to synchronously
when needed.

Also, move the code to net/llc/llc_conn.c, which is apparently
a better place.

Reported-by: <syzbot+f922284c18ea23a8e457@syzkaller.appspotmail.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/llc_conn.h

@@ -97,6 +97,7 @@ static __inline__ char llc_backlog_type(struct sk_buff *skb)
 
 struct sock *llc_sk_alloc(struct net *net, int family, gfp_t priority,
 			  struct proto *prot, int kern);
+void llc_sk_stop_all_timers(struct sock *sk, bool sync);
 void llc_sk_free(struct sock *sk);
 
 void llc_sk_reset(struct sock *sk);

net/llc/llc_c_ac.c

@@ -1099,14 +1099,7 @@ int llc_conn_ac_inc_tx_win_size(struct sock *sk, struct sk_buff *skb)
 
 int llc_conn_ac_stop_all_timers(struct sock *sk, struct sk_buff *skb)
 {
-	struct llc_sock *llc = llc_sk(sk);
-
-	del_timer(&llc->pf_cycle_timer.timer);
-	del_timer(&llc->ack_timer.timer);
-	del_timer(&llc->rej_sent_timer.timer);
-	del_timer(&llc->busy_state_timer.timer);
-	llc->ack_must_be_send = 0;
-	llc->ack_pf = 0;
+	llc_sk_stop_all_timers(sk, false);
 	return 0;
 }
 

net/llc/llc_conn.c

@@ -961,6 +961,26 @@ struct sock *llc_sk_alloc(struct net *net, int family, gfp_t priority, struct pr
 	return sk;
 }
 
+void llc_sk_stop_all_timers(struct sock *sk, bool sync)
+{
+	struct llc_sock *llc = llc_sk(sk);
+
+	if (sync) {
+		del_timer_sync(&llc->pf_cycle_timer.timer);
+		del_timer_sync(&llc->ack_timer.timer);
+		del_timer_sync(&llc->rej_sent_timer.timer);
+		del_timer_sync(&llc->busy_state_timer.timer);
+	} else {
+		del_timer(&llc->pf_cycle_timer.timer);
+		del_timer(&llc->ack_timer.timer);
+		del_timer(&llc->rej_sent_timer.timer);
+		del_timer(&llc->busy_state_timer.timer);
+	}
+
+	llc->ack_must_be_send = 0;
+	llc->ack_pf = 0;
+}
+
 /**
  *	llc_sk_free - Frees a LLC socket
  *	@sk - socket to free
@@ -973,7 +993,7 @@ void llc_sk_free(struct sock *sk)
 
 	llc->state = LLC_CONN_OUT_OF_SVC;
 	/* Stop all (possibly) running timers */
-	llc_conn_ac_stop_all_timers(sk, NULL);
+	llc_sk_stop_all_timers(sk, true);
 #ifdef DEBUG_LLC_CONN_ALLOC
 	printk(KERN_INFO "%s: unackq=%d, txq=%d\n", __func__,
 		skb_queue_len(&llc->pdu_unack_q),