linux-kernel - [PATCH 4.8 076/140] NFSD: fix corruption in notifier registration

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20161026122223.627687647@linuxfoundation.org>
Date:   Wed, 26 Oct 2016 14:22:16 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Vasily Averin <vvs@...tuozzo.com>,
        Jeff Layton <jlayton@...hat.com>,
        "J. Bruce Fields" <bfields@...hat.com>
Subject: [PATCH 4.8 076/140] NFSD: fix corruption in notifier registration

4.8-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Vasily Averin <vvs@...tuozzo.com>

commit 1eca45f8a840987d0df355e0176921653e4f7ec2 upstream.

By design notifier can be registered once only, however nfsd registers
the same inetaddr notifiers per net-namespace.  When this happen it
corrupts list of notifiers, as result some notifiers can be not called
on proper event, traverse on list can be cycled forever, and second
unregister can access already freed memory.

fixes: 36684996 ("nfsd: Register callbacks on the inetaddr_chain and inet6addr_chain")
Signed-off-by: Vasily Averin <vvs@...tuozzo.com>
Reviewed-by: Jeff Layton <jlayton@...hat.com>
Signed-off-by: J. Bruce Fields <bfields@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/nfsd/nfssvc.c |   18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -366,14 +366,21 @@ static struct notifier_block nfsd_inet6a
 };
 #endif
 
+/* Only used under nfsd_mutex, so this atomic may be overkill: */
+static atomic_t nfsd_notifier_refcount = ATOMIC_INIT(0);
+
 static void nfsd_last_thread(struct svc_serv *serv, struct net *net)
 {
 	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
 
-	unregister_inetaddr_notifier(&nfsd_inetaddr_notifier);
+	/* check if the notifier still has clients */
+	if (atomic_dec_return(&nfsd_notifier_refcount) == 0) {
+		unregister_inetaddr_notifier(&nfsd_inetaddr_notifier);
 #if IS_ENABLED(CONFIG_IPV6)
-	unregister_inet6addr_notifier(&nfsd_inet6addr_notifier);
+		unregister_inet6addr_notifier(&nfsd_inet6addr_notifier);
 #endif
+	}
+
 	/*
 	 * write_ports can create the server without actually starting
 	 * any threads--if we get shut down before any threads are
@@ -488,10 +495,13 @@ int nfsd_create_serv(struct net *net)
 	}
 
 	set_max_drc();
-	register_inetaddr_notifier(&nfsd_inetaddr_notifier);
+	/* check if the notifier is already set */
+	if (atomic_inc_return(&nfsd_notifier_refcount) == 1) {
+		register_inetaddr_notifier(&nfsd_inetaddr_notifier);
 #if IS_ENABLED(CONFIG_IPV6)
-	register_inet6addr_notifier(&nfsd_inet6addr_notifier);
+		register_inet6addr_notifier(&nfsd_inet6addr_notifier);
 #endif
+	}
 	do_gettimeofday(&nn->nfssvc_boot);		/* record boot time */
 	return 0;
 }