From 2726bc726b8755f32ed5911711788f3e71824995 Mon Sep 17 00:00:00 2001 From: Xie He Date: Sun, 27 Dec 2020 18:53:39 -0800 Subject: [PATCH] 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 Signed-off-by: Xie He Signed-off-by: David S. Miller --- drivers/net/wan/hdlc_ppp.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/drivers/net/wan/hdlc_ppp.c b/drivers/net/wan/hdlc_ppp.c index 64f8556513369..261b53fc8e04c 100644 --- 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: -- 2.39.5