netdev - Re: net/l2tp:BUG: KASAN: use-after-free in l2tp_ip6

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Message-ID: <47543f61-8a36-9566-4b7d-f5cf7dbd9f56@gmail.com>
Date:   Thu, 17 Nov 2016 18:56:25 +0800
From:   Baozeng Ding <sploving1@...il.com>
To:     Guillaume Nault <g.nault@...halink.fr>,
        Cong Wang <xiyou.wangcong@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: net/l2tp:BUG: KASAN: use-after-free in l2tp_ip6_close


Hello Guillaume,
On 2016/11/17 5:07, Guillaume Nault wrote:
> On Wed, Nov 16, 2016 at 11:08:23AM -0800, Cong Wang wrote:
>> On Wed, Nov 16, 2016 at 8:30 AM, Guillaume Nault <g.nault@...halink.fr> wrote:
>>> diff --git a/net/l2tp/l2tp_ip.c b/net/l2tp/l2tp_ip.c
>>> index fce25af..982f6c4 100644
>>> --- a/net/l2tp/l2tp_ip.c
>>> +++ b/net/l2tp/l2tp_ip.c
>>> @@ -251,8 +251,6 @@ static int l2tp_ip_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len)
>>>         int ret;
>>>         int chk_addr_ret;
>>>
>>> -       if (!sock_flag(sk, SOCK_ZAPPED))
>>> -               return -EINVAL;
>>>         if (addr_len < sizeof(struct sockaddr_l2tpip))
>>>                 return -EINVAL;
>>>         if (addr->l2tp_family != AF_INET)
>>> @@ -267,6 +265,9 @@ static int l2tp_ip_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len)
>>>         read_unlock_bh(&l2tp_ip_lock);
>>>
>>>         lock_sock(sk);
>>> +       if (!sock_flag(sk, SOCK_ZAPPED))
>>> +               goto out;
>>> +
>>>         if (sk->sk_state != TCP_CLOSE || addr_len < sizeof(struct sockaddr_l2tpip))
>>>                 goto out;
>>>
>>> diff --git a/net/l2tp/l2tp_ip6.c b/net/l2tp/l2tp_ip6.c
>>> index ad3468c..9978d01 100644
>>> --- a/net/l2tp/l2tp_ip6.c
>>> +++ b/net/l2tp/l2tp_ip6.c
>>> @@ -269,8 +269,6 @@ static int l2tp_ip6_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len)
>>>         int addr_type;
>>>         int err;
>>>
>>> -       if (!sock_flag(sk, SOCK_ZAPPED))
>>> -               return -EINVAL;
>>>         if (addr->l2tp_family != AF_INET6)
>>>                 return -EINVAL;
>>>         if (addr_len < sizeof(*addr))
>>> @@ -296,6 +294,9 @@ static int l2tp_ip6_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len)
>>>         lock_sock(sk);
>>>
>>>         err = -EINVAL;
>>> +       if (!sock_flag(sk, SOCK_ZAPPED))
>>> +               goto out_unlock;
>>> +
>>>         if (sk->sk_state != TCP_CLOSE)
>>>                 goto out_unlock;
>>
>>
>> Makes sense, it should prevent a concurrent caller adding the socket
>> into bind table
>> twice after passing __l2tp_ip_bind_lookup() check.
> 
> Yes, and the __l2tp_ip_bind_lookup() call is also racy. But, by
> properly checking the SOCK_ZAPPED flag, we probably can remove this
> call entirely.
> 
> For now, I only wanted to make sure the issue was well identified. I'll
> submit a more complete patch for net (with protected SOCK_ZAPPED check
> in l2tp_ip_connect() too).
>
The patch fixes the issues both for l2tp_ip and l2tp_ip6

Tested-by: Baozeng Ding <sploving1@...il.com>


Best Regards,
Baozeng Ding