netdev - Re: [BUG] kernel stack corruption during/after Netlabel error

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Date:   Thu, 30 Nov 2017 10:16:26 -0800
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        David Ahern <dsahern@...il.com>,
        James Morris <james.l.morris@...cle.com>
Cc:     Paul Moore <paul@...l-moore.com>, netdev@...r.kernel.org,
        Stephen Smalley <sds@...ho.nsa.gov>, selinux@...ho.nsa.gov,
        LSM <linux-security-module@...r.kernel.org>
Subject: Re: [BUG] kernel stack corruption during/after Netlabel error

On 11/30/2017 9:57 AM, Eric Dumazet wrote:
> On Thu, 2017-11-30 at 10:30 -0700, David Ahern wrote:
>> On 11/30/17 8:44 AM, David Ahern wrote:
>>> On 11/30/17 3:50 AM, Eric Dumazet wrote:
>>>> @@ -1631,24 +1659,6 @@ int tcp_v4_rcv(struct sk_buff *skb)
>>>>  
>>>>  	th = (const struct tcphdr *)skb->data;
>>>>  	iph = ip_hdr(skb);
>>>> -	/* This is tricky : We move IPCB at its correct location
>>>> into TCP_SKB_CB()
>>>> -	 * barrier() makes sure compiler wont play
>>>> fool^Waliasing games.
>>>> -	 */
>>>> -	memmove(&TCP_SKB_CB(skb)->header.h4, IPCB(skb),
>>>> -		sizeof(struct inet_skb_parm));
>>>> -	barrier();
>>>> -
>>>> -	TCP_SKB_CB(skb)->seq = ntohl(th->seq);
>>>> -	TCP_SKB_CB(skb)->end_seq = (TCP_SKB_CB(skb)->seq + th-
>>>>> syn + th->fin +
>>>> -				    skb->len - th->doff * 4);
>>>> -	TCP_SKB_CB(skb)->ack_seq = ntohl(th->ack_seq);
>>>> -	TCP_SKB_CB(skb)->tcp_flags = tcp_flag_byte(th);
>>>> -	TCP_SKB_CB(skb)->tcp_tw_isn = 0;
>>>> -	TCP_SKB_CB(skb)->ip_dsfield = ipv4_get_dsfield(iph);
>>>> -	TCP_SKB_CB(skb)->sacked	 = 0;
>>>> -	TCP_SKB_CB(skb)->has_rxtstamp =
>>>> -			skb->tstamp || skb_hwtstamps(skb)-
>>>>> hwtstamp;
>>>> -
>>>>  lookup:
>>>>  	sk = __inet_lookup_skb(&tcp_hashinfo, skb,
>>>> __tcp_hdrlen(th), th->source,
>>>>  			       th->dest, sdif, &refcounted);
>>> I believe moving the above is going to affect lookups with VRF. Let
>>> me
>>> take a look before this gets committed.
>>>
>> Eric:
>>
>> Can you add this to the patch? Fixes socket lookups with VRF which
>> stashes a flag in the cb.

I've done my testing and it works both ways for Smack.


>>
>> Thanks,
>>
>> diff --git a/include/net/tcp.h b/include/net/tcp.h
>> index 4e09398009c1..6c020015d556 100644
>> --- a/include/net/tcp.h
>> +++ b/include/net/tcp.h
>> @@ -849,7 +849,7 @@ static inline bool inet_exact_dif_match(struct
>> net
>> *net, struct sk_buff *skb)
>>  {
>>  #if IS_ENABLED(CONFIG_NET_L3_MASTER_DEV)
>>         if (!net->ipv4.sysctl_tcp_l3mdev_accept &&
>> -           skb && ipv4_l3mdev_skb(TCP_SKB_CB(skb)->header.h4.flags))
>> +           skb && ipv4_l3mdev_skb(IPCB(skb)->flags))
>>                 return true;
>>  #endif
>>         return false;
>
> I wonder if this should not be in a separate patch ?
>
> Bug was added in 971f10eca186cab238c49daa91f703c5a001b0b1 ("tcp: better
> TCP_SKB_CB layout to reduce cache line misses")  in linux 3.18
>
> While VRF was added later.
>
> If you agree, I will prepare a patch series, with different Fixes tag
> so that David can decide which path needs to be backported into each
> stable version.
>
> Thanks.
>
>