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From:   Sasha Levin <Alexander.Levin@microsoft.com>
To:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
CC:     Vasily Averin <vvs@virtuozzo.com>,
        "J . Bruce Fields" <bfields@redhat.com>,
        Sasha Levin <Alexander.Levin@microsoft.com>
Subject: [PATCH AUTOSEL for 4.14 061/100] race of lockd inetaddr notifiers vs
 nlmsvc_rqst change
Thread-Topic: [PATCH AUTOSEL for 4.14 061/100] race of lockd inetaddr
 notifiers vs nlmsvc_rqst change
Thread-Index: AQHTlMnjH+Vk2IpxikmcJgfUYnQemg==
Date:   Wed, 24 Jan 2018 04:14:55 +0000
Message-ID: <20180124041414.32065-61-alexander.levin@microsoft.com>
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From: Vasily Averin <vvs@virtuozzo.com>

[ Upstream commit 6b18dd1c03e07262ea0866084856b2a3c5ba8d09 ]

lockd_inet[6]addr_event use nlmsvc_rqst without taken nlmsvc_mutex,
nlmsvc_rqst can be changed during execution of notifiers and crash the host=
.

Patch enables access to nlmsvc_rqst only when it was correctly initialized
and delays its cleanup until notifiers are no longer in use.

Note that nlmsvc_rqst can be temporally set to ERR_PTR, so the "if
(nlmsvc_rqst)" check in notifiers is insufficient on its own.

Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Tested-by: Scott Mayhew <smayhew@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
 fs/lockd/svc.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/fs/lockd/svc.c b/fs/lockd/svc.c
index 45e96549ebd2..809cbccbad28 100644
--- a/fs/lockd/svc.c
+++ b/fs/lockd/svc.c
@@ -57,6 +57,9 @@ static struct task_struct	*nlmsvc_task;
 static struct svc_rqst		*nlmsvc_rqst;
 unsigned long			nlmsvc_timeout;
=20
+atomic_t nlm_ntf_refcnt =3D ATOMIC_INIT(0);
+DECLARE_WAIT_QUEUE_HEAD(nlm_ntf_wq);
+
 unsigned int lockd_net_id;
=20
 /*
@@ -292,7 +295,8 @@ static int lockd_inetaddr_event(struct notifier_block *=
this,
 	struct in_ifaddr *ifa =3D (struct in_ifaddr *)ptr;
 	struct sockaddr_in sin;
=20
-	if (event !=3D NETDEV_DOWN)
+	if ((event !=3D NETDEV_DOWN) ||
+	    !atomic_inc_not_zero(&nlm_ntf_refcnt))
 		goto out;
=20
 	if (nlmsvc_rqst) {
@@ -303,6 +307,8 @@ static int lockd_inetaddr_event(struct notifier_block *=
this,
 		svc_age_temp_xprts_now(nlmsvc_rqst->rq_server,
 			(struct sockaddr *)&sin);
 	}
+	atomic_dec(&nlm_ntf_refcnt);
+	wake_up(&nlm_ntf_wq);
=20
 out:
 	return NOTIFY_DONE;
@@ -319,7 +325,8 @@ static int lockd_inet6addr_event(struct notifier_block =
*this,
 	struct inet6_ifaddr *ifa =3D (struct inet6_ifaddr *)ptr;
 	struct sockaddr_in6 sin6;
=20
-	if (event !=3D NETDEV_DOWN)
+	if ((event !=3D NETDEV_DOWN) ||
+	    !atomic_inc_not_zero(&nlm_ntf_refcnt))
 		goto out;
=20
 	if (nlmsvc_rqst) {
@@ -331,6 +338,8 @@ static int lockd_inet6addr_event(struct notifier_block =
*this,
 		svc_age_temp_xprts_now(nlmsvc_rqst->rq_server,
 			(struct sockaddr *)&sin6);
 	}
+	atomic_dec(&nlm_ntf_refcnt);
+	wake_up(&nlm_ntf_wq);
=20
 out:
 	return NOTIFY_DONE;
@@ -347,10 +356,12 @@ static void lockd_unregister_notifiers(void)
 #if IS_ENABLED(CONFIG_IPV6)
 	unregister_inet6addr_notifier(&lockd_inet6addr_notifier);
 #endif
+	wait_event(nlm_ntf_wq, atomic_read(&nlm_ntf_refcnt) =3D=3D 0);
 }
=20
 static void lockd_svc_exit_thread(void)
 {
+	atomic_dec(&nlm_ntf_refcnt);
 	lockd_unregister_notifiers();
 	svc_exit_thread(nlmsvc_rqst);
 }
@@ -375,6 +386,7 @@ static int lockd_start_svc(struct svc_serv *serv)
 		goto out_rqst;
 	}
=20
+	atomic_inc(&nlm_ntf_refcnt);
 	svc_sock_update_bufs(serv);
 	serv->sv_maxconn =3D nlm_max_connections;
=20
--=20
2.11.0