From 1eca45f8a840987d0df355e0176921653e4f7ec2 Mon Sep 17 00:00:00 2001 From: Vasily Averin Date: Wed, 21 Sep 2016 15:33:05 +0300 Subject: [PATCH] NFSD: fix corruption in notifier registration 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. Cc: stable@vger.kernel.org fixes: 36684996 ("nfsd: Register callbacks on the inetaddr_chain and inet6addr_chain") Signed-off-by: Vasily Averin Reviewed-by: Jeff Layton Cc: stable@vger.kernel.org Signed-off-by: J. Bruce Fields --- fs/nfsd/nfssvc.c | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-) diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c index 45007acaf364..a2b65fc56dd6 100644 --- a/fs/nfsd/nfssvc.c +++ b/fs/nfsd/nfssvc.c @@ -366,14 +366,21 @@ static struct notifier_block nfsd_inet6addr_notifier = { }; #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; } -- 2.20.1