linux-kernel - [PATCH 3.10 109/139] ipv6: avoid unregistering inet6

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Message-Id: <1509571624-5001-10-git-send-email-w@1wt.eu>
Date:   Wed,  1 Nov 2017 22:26:34 +0100
From:   Willy Tarreau <w@....eu>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux@...ck-us.net
Cc:     WANG Cong <xiyou.wangcong@...il.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Daniel Lezcano <dlezcano@...ibm.com>,
        David Ahern <dsahern@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Willy Tarreau <w@....eu>
Subject: [PATCH 3.10 109/139] ipv6: avoid unregistering inet6_dev for loopback

From: WANG Cong <xiyou.wangcong@...il.com>

commit 60abc0be96e00ca71bac083215ac91ad2e575096 upstream.

The per netns loopback_dev->ip6_ptr is unregistered and set to
NULL when its mtu is set to smaller than IPV6_MIN_MTU, this
leads to that we could set rt->rt6i_idev NULL after a
rt6_uncached_list_flush_dev() and then crash after another
call.

In this case we should just bring its inet6_dev down, rather
than unregistering it, at least prior to commit 176c39af29bc
("netns: fix addrconf_ifdown kernel panic") we always
override the case for loopback.

Thanks a lot to Andrey for finding a reliable reproducer.

Fixes: 176c39af29bc ("netns: fix addrconf_ifdown kernel panic")
Reported-by: Andrey Konovalov <andreyknvl@...gle.com>
Cc: Andrey Konovalov <andreyknvl@...gle.com>
Cc: Daniel Lezcano <dlezcano@...ibm.com>
Cc: David Ahern <dsahern@...il.com>
Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
Acked-by: David Ahern <dsahern@...il.com>
Tested-by: Andrey Konovalov <andreyknvl@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

Signed-off-by: Willy Tarreau <w@....eu>
---
 net/ipv6/addrconf.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 9c4aa2e..5ea5f77 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -2892,6 +2892,7 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
 {
 	struct net_device *dev = (struct net_device *) data;
 	struct inet6_dev *idev = __in6_dev_get(dev);
+	struct net *net = dev_net(dev);
 	int run_pending = 0;
 	int err;

@@ -2988,7 +2989,7 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
 			 * IPV6_MIN_MTU stop IPv6 on this interface.
 			 */
 			if (dev->mtu < IPV6_MIN_MTU)
-				addrconf_ifdown(dev, 1);
+				addrconf_ifdown(dev, dev != net->loopback_dev);
 		}
 		break;

-- 
2.8.0.rc2.1.gbe9624a