diff mbox series

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

Message ID 20201228001425.821582-1-xie.he.0141@gmail.com (mailing list archive)
State Superseded
Delegated to: Netdev Maintainers
Headers show
Series [net] net: hdlc_ppp: Fix issues when mod_timer is called while timer is running | expand

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netdev/fixes_present fail Series targets non-next tree, but doesn't contain any Fixes tags
netdev/patch_count success Link
netdev/tree_selection success Clearly marked for net
netdev/subject_prefix success Link
netdev/cc_maintainers success CCed 4 of 4 maintainers
netdev/source_inline success Was 0 now: 0
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netdev/module_param success Was 0 now: 0
netdev/build_32bit success Errors and warnings before: 0 this patch: 0
netdev/kdoc success Errors and warnings before: 0 this patch: 0
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netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 13 lines checked
netdev/build_allmodconfig_warn success Errors and warnings before: 0 this patch: 0
netdev/header_inline success Link
netdev/stable success Stable not CCed

Commit Message

Xie He Dec. 28, 2020, 12:14 a.m. UTC
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.

Cc: Krzysztof Halasa <khc@pm.waw.pl>
Signed-off-by: Xie He <xie.he.0141@gmail.com>
---
 drivers/net/wan/hdlc_ppp.c | 7 +++++++
 1 file changed, 7 insertions(+)
diff mbox series

Patch

diff --git a/drivers/net/wan/hdlc_ppp.c b/drivers/net/wan/hdlc_ppp.c
index 64f855651336..261b53fc8e04 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: