[BUG] kernel stack corruption during/after Netlabel error

[eric.dumazet@gmail.com (Eric Dumazet)]

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.
> 
> 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.

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