netfilter: ipt_CLUSTERIP: fix a race condition of proc file creation

There is a race condition between clusterip_config_entry_put()
and clusterip_config_init(), after we release the spinlock in
clusterip_config_entry_put(), a new proc file with a same IP could
be created immediately since it is already removed from the configs
list, therefore it triggers this warning:

------------[ cut here ]------------
proc_dir_entry 'ipt_CLUSTERIP/172.20.0.170' already registered
WARNING: CPU: 1 PID: 4152 at fs/proc/generic.c:330 proc_register+0x2a4/0x370 fs/proc/generic.c:329
Kernel panic - not syncing: panic_on_warn set ...

As a quick fix, just move the proc_remove() inside the spinlock.

Reported-by: <syzbot+03218bcdba6aa76441a3@syzkaller.appspotmail.com>
Fixes: 6c5d5cfbe3c5 ("netfilter: ipt_CLUSTERIP: check duplicate config when initializing")
Tested-by: Paolo Abeni <pabeni@redhat.com>
Cc: Xin Long <lucien.xin@gmail.com>
Cc: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Reviewed-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/ipv4/netfilter/ipt_CLUSTERIP.c b/net/ipv4/netfilter/ipt_CLUSTERIP.c
index 3a84a60..1ff72b8 100644 (file)
--- a/net/ipv4/netfilter/ipt_CLUSTERIP.c
+++ b/net/ipv4/netfilter/ipt_CLUSTERIP.c
@@ -107,12 +107,6 @@ clusterip_config_entry_put(struct net *net, struct clusterip_config *c)
 
        local_bh_disable();
        if (refcount_dec_and_lock(&c->entries, &cn->lock)) {
-               list_del_rcu(&c->list);
-               spin_unlock(&cn->lock);
-               local_bh_enable();
-
-               unregister_netdevice_notifier(&c->notifier);
-
                /* In case anyone still accesses the file, the open/close
                 * functions are also incrementing the refcount on their own,
                 * so it's safe to remove the entry even if it's in use. */
@@ -120,6 +114,12 @@ clusterip_config_entry_put(struct net *net, struct clusterip_config *c)
                if (cn->procdir)
                        proc_remove(c->pde);
 #endif
+               list_del_rcu(&c->list);
+               spin_unlock(&cn->lock);
+               local_bh_enable();
+
+               unregister_netdevice_notifier(&c->notifier);
+
                return;
        }
        local_bh_enable();