netdev - [PATCH net v2] ipv6/addrconf: fix a potential refcount underflow for idev

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Date: Sat, 8 Jul 2023 14:59:10 +0800
From: Ziyang Xuan <william.xuanziyang@...wei.com>
To: <davem@...emloft.net>, <dsahern@...nel.org>, <edumazet@...gle.com>,
	<kuba@...nel.org>, <pabeni@...hat.com>, <netdev@...r.kernel.org>,
	<hannes@...essinduktion.org>, <fbl@...hat.com>
Subject: [PATCH net v2] ipv6/addrconf: fix a potential refcount underflow for idev

Now in addrconf_mod_rs_timer(), reference idev depends on whether
rs_timer is not pending. Then modify rs_timer timeout.

There is a time gap in [1], during which if the pending rs_timer
becomes not pending. It will miss to hold idev, but the rs_timer
is activated. Thus rs_timer callback function addrconf_rs_timer()
will be executed and put idev later without holding idev. A refcount
underflow issue for idev can be caused by this.

	if (!timer_pending(&idev->rs_timer))
		in6_dev_hold(idev);
		  <--------------[1]
	mod_timer(&idev->rs_timer, jiffies + when);

To fix the issue, hold idev if mod_timer() return 0.

Fixes: b7b1bfce0bb6 ("ipv6: split duplicate address detection and router solicitation timer")
Suggested-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Ziyang Xuan <william.xuanziyang@...wei.com>
---
v2:
  - Do not hold idev anyway firstly.
---
 net/ipv6/addrconf.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 5479da08ef40..e5213e598a04 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -318,9 +318,8 @@ static void addrconf_del_dad_work(struct inet6_ifaddr *ifp)
 static void addrconf_mod_rs_timer(struct inet6_dev *idev,
 				  unsigned long when)
 {
-	if (!timer_pending(&idev->rs_timer))
+	if (!mod_timer(&idev->rs_timer, jiffies + when))
 		in6_dev_hold(idev);
-	mod_timer(&idev->rs_timer, jiffies + when);
 }
 
 static void addrconf_mod_dad_work(struct inet6_ifaddr *ifp,
-- 
2.25.1