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

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Message-ID: <d29937fd-dd04-8568-f89c-505ff725761a@gmail.com>
Date:   Thu, 30 Nov 2017 10:30:51 -0700
From:   David Ahern <dsahern@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        Casey Schaufler <casey@...aufler-ca.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 11/30/17 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.

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;