net: hdlc_ppp: Fix issues when mod_timer is called while timer is running

ppp_cp_event is called directly or indirectly by ppp_rx with "ppp->lock"
held. It may call mod_timer to add a new timer. However, at the same time
ppp_timer may be already running and waiting for "ppp->lock". In this
case, there's no need for ppp_timer to continue running and it can just
exit.

If we let ppp_timer continue running, it may call add_timer. This causes
kernel panic because add_timer can't be called with a timer pending.
This patch fixes this problem.

Fixes: 6a8cbb2586cf ("WAN: new synchronous PPP implementation for generic HDLC.")
Cc: Krzysztof Halasa <khc@pm.waw.pl>
Signed-off-by: Xie He <xie.he.0141@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/wan/hdlc_ppp.c b/drivers/net/wan/hdlc_ppp.c
index 64f855651336963eaa2401669f7c422d9e376ffd..261b53fc8e04cb8c141eba8c29ff155b73b069c1 100644 (file)
--- a/drivers/net/wan/hdlc_ppp.c
+++ b/drivers/net/wan/hdlc_ppp.c
@@ -569,6 +569,13 @@ static void ppp_timer(struct timer_list *t)
        unsigned long flags;
 
        spin_lock_irqsave(&ppp->lock, flags);
+       /* mod_timer could be called after we entered this function but
+        * before we got the lock.
+        */
+       if (timer_pending(&proto->timer)) {
+               spin_unlock_irqrestore(&ppp->lock, flags);
+               return;
+       }
        switch (proto->state) {
        case STOPPING:
        case REQ_SENT: