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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: e022c2f07a ("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>
This commit is contained in:
Xie He 2020-12-27 18:53:39 -08:00 committed by David S. Miller
parent 9b22fece78
commit 1fef73597f
1 changed files with 7 additions and 0 deletions
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7
drivers/net/wan/hdlc_ppp.c
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@ -569,6 +569,13 @@ static void ppp_timer(struct timer_list *t)
unsigned long flags; unsigned long flags;
spin_lock_irqsave(&ppp->lock, 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) { switch (proto->state) {
case STOPPING: case STOPPING:
case REQ_SENT: case REQ_SENT: