Re: [Patch net] ipt_CLUSTERIP: fix a race condition of proc file creation

[Xin Long <lucien.xin@gmail.com>]

On Thu, Feb 8, 2018 at 1:59 PM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
> 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>
> ---
>  net/ipv4/netfilter/ipt_CLUSTERIP.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/net/ipv4/netfilter/ipt_CLUSTERIP.c b/net/ipv4/netfilter/ipt_CLUSTERIP.c
> index 3a84a60f6b39..1ff72b87a066 100644
> --- 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();
> --
> 2.13.0
>
Reviewed-by: Xin Long <lucien.xin@gmail.com>