netdev - [PATCH] ipv6: acquire write lock for addr_list in dev_forward

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Date:   Wed, 16 Mar 2022 00:02:23 +0100
From:   Niels Dossche <dossche.niels@...il.com>
To:     netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Niels Dossche <dossche.niels@...il.com>
Subject: [PATCH] ipv6: acquire write lock for addr_list in dev_forward_change

No path towards dev_forward_change (common ancestor of paths is in
addrconf_fixup_forwarding) acquires idev->lock for idev->addr_list.
Since addrconf_{join,leave}_anycast acquire a write lock on addr_list in
__ipv6_dev_ac_inc and __ipv6_dev_ac_dec, temporarily unlock when calling
addrconf_{join,leave}_anycast analogous to how it's done in
addrconf_ifdown.

Signed-off-by: Niels Dossche <dossche.niels@...il.com>
---
 net/ipv6/addrconf.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index f908e2fd30b2..4055ded4b7bf 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -818,14 +818,18 @@ static void dev_forward_change(struct inet6_dev *idev)
 		}
 	}
 
+	write_lock_bh(&idev->lock);
 	list_for_each_entry(ifa, &idev->addr_list, if_list) {
 		if (ifa->flags&IFA_F_TENTATIVE)
 			continue;
+		write_unlock_bh(&idev->lock);
 		if (idev->cnf.forwarding)
 			addrconf_join_anycast(ifa);
 		else
 			addrconf_leave_anycast(ifa);
+		write_lock_bh(&idev->lock);
 	}
+	write_unlock_bh(&idev->lock);
 	inet6_netconf_notify_devconf(dev_net(dev), RTM_NEWNETCONF,
 				     NETCONFA_FORWARDING,
 				     dev->ifindex, &idev->cnf);
-- 
2.35.1