Commit 09d88553 authored Dec 27, 2020 by Xie He Committed by Greg Kroah-Hartman Jan 12, 2021

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



[ Upstream commit 1fef73597fa545c35fddc953979013882fbd4e55 ]

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: e022c2f0 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 53f31209

drivers/net/wan/hdlc_ppp.c

+7 −0

Original line number	Diff line number	Diff line
		@@ -572,6 +572,13 @@ static void ppp_timer(unsigned long arg)
		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: