[BUG] kernel stack corruption during/after Netlabel error

Casey Schaufler casey at schaufler-ca.com
Thu Nov 30 14:33:17 UTC 2017


On 11/30/2017 2:50 AM, Eric Dumazet wrote:
> On Wed, 2017-11-29 at 19:16 -0800, Casey Schaufler wrote:
>> On 11/29/2017 4:31 PM, James Morris wrote:
>>> On Wed, 29 Nov 2017, Casey Schaufler wrote:
>>>
>>>> I see that there is a proposed fix later in the thread, but I
>>>> don't see
>>>> the patch. Could you send it to me, so I can try it on my
>>>> problem?
>>> Forwarded off-list.
>> The patch does fix the problem I was seeing in Smack.
> Can you guys test the following more complete patch ?

Building now. I should have results soon.

>
> It should cover IPv4 and IPv6, and also the corner cases.
>
> ( Note that I squashed ipv6 fix in https://patchwork.ozlabs.org/patch/8
> 42844/ that I spotted while cooking this patch )
>
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index c6bc0c4d19c624888b0d0b5a4246c7183edf63f5..77ea45da0fe9c746907a312989658af3ad3b198d 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -1591,6 +1591,34 @@ int tcp_filter(struct sock *sk, struct sk_buff *skb)
>  }
>  EXPORT_SYMBOL(tcp_filter);
>  
> +static void tcp_v4_restore_cb(struct sk_buff *skb)
> +{
> +	memmove(IPCB(skb), &TCP_SKB_CB(skb)->header.h4,
> +		sizeof(struct inet_skb_parm));
> +}
> +
> +static void tcp_v4_fill_cb(struct sk_buff *skb, const struct iphdr *iph,
> +			   const struct tcphdr *th)
> +{
> +	/* 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;
> +}
> +
>  /*
>   *	From tcp_input.c
>   */
> @@ -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);
> @@ -1679,14 +1689,19 @@ int tcp_v4_rcv(struct sk_buff *skb)
>  		sock_hold(sk);
>  		refcounted = true;
>  		nsk = NULL;
> -		if (!tcp_filter(sk, skb))
> +		if (!tcp_filter(sk, skb)) {
> +			th = (const struct tcphdr *)skb->data;
> +			iph = ip_hdr(skb);
> +			tcp_v4_fill_cb(skb, iph, th);
>  			nsk = tcp_check_req(sk, skb, req, false);
> +		}
>  		if (!nsk) {
>  			reqsk_put(req);
>  			goto discard_and_relse;
>  		}
>  		if (nsk == sk) {
>  			reqsk_put(req);
> +			tcp_v4_restore_cb(skb);
>  		} else if (tcp_child_process(sk, nsk, skb)) {
>  			tcp_v4_send_reset(nsk, skb);
>  			goto discard_and_relse;
> @@ -1712,6 +1727,7 @@ int tcp_v4_rcv(struct sk_buff *skb)
>  		goto discard_and_relse;
>  	th = (const struct tcphdr *)skb->data;
>  	iph = ip_hdr(skb);
> +	tcp_v4_fill_cb(skb, iph, th);
>  
>  	skb->dev = NULL;
>  
> @@ -1742,6 +1758,8 @@ int tcp_v4_rcv(struct sk_buff *skb)
>  	if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb))
>  		goto discard_it;
>  
> +	tcp_v4_fill_cb(skb, iph, th);
> +
>  	if (tcp_checksum_complete(skb)) {
>  csum_error:
>  		__TCP_INC_STATS(net, TCP_MIB_CSUMERRORS);
> @@ -1768,6 +1786,8 @@ int tcp_v4_rcv(struct sk_buff *skb)
>  		goto discard_it;
>  	}
>  
> +	tcp_v4_fill_cb(skb, iph, th);
> +
>  	if (tcp_checksum_complete(skb)) {
>  		inet_twsk_put(inet_twsk(sk));
>  		goto csum_error;
> @@ -1784,6 +1804,7 @@ int tcp_v4_rcv(struct sk_buff *skb)
>  		if (sk2) {
>  			inet_twsk_deschedule_put(inet_twsk(sk));
>  			sk = sk2;
> +			tcp_v4_restore_cb(skb);
>  			refcounted = false;
>  			goto process;
>  		}
> diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
> index 6bb98c93edfe2ed2f16fe5229605f8108cfc7f9a..1f04ec0e4a7aa2c11b8ee27cbdd4067b5bcf32e5 100644
> --- a/net/ipv6/tcp_ipv6.c
> +++ b/net/ipv6/tcp_ipv6.c
> @@ -1454,7 +1454,6 @@ static int tcp_v6_rcv(struct sk_buff *skb)
>  		struct sock *nsk;
>  
>  		sk = req->rsk_listener;
> -		tcp_v6_fill_cb(skb, hdr, th);
>  		if (tcp_v6_inbound_md5_hash(sk, skb)) {
>  			sk_drops_add(sk, skb);
>  			reqsk_put(req);
> @@ -1467,8 +1466,12 @@ static int tcp_v6_rcv(struct sk_buff *skb)
>  		sock_hold(sk);
>  		refcounted = true;
>  		nsk = NULL;
> -		if (!tcp_filter(sk, skb))
> +		if (!tcp_filter(sk, skb)) {
> +			th = (const struct tcphdr *)skb->data;
> +			hdr = ipv6_hdr(skb);
> +			tcp_v6_fill_cb(skb, hdr, th);
>  			nsk = tcp_check_req(sk, skb, req, false);
> +		}
>  		if (!nsk) {
>  			reqsk_put(req);
>  			goto discard_and_relse;
> @@ -1492,8 +1495,6 @@ static int tcp_v6_rcv(struct sk_buff *skb)
>  	if (!xfrm6_policy_check(sk, XFRM_POLICY_IN, skb))
>  		goto discard_and_relse;
>  
> -	tcp_v6_fill_cb(skb, hdr, th);
> -
>  	if (tcp_v6_inbound_md5_hash(sk, skb))
>  		goto discard_and_relse;
>  
> @@ -1501,6 +1502,7 @@ static int tcp_v6_rcv(struct sk_buff *skb)
>  		goto discard_and_relse;
>  	th = (const struct tcphdr *)skb->data;
>  	hdr = ipv6_hdr(skb);
> +	tcp_v6_fill_cb(skb, hdr, th);
>  
>  	skb->dev = NULL;
>  
> @@ -1590,7 +1592,6 @@ static int tcp_v6_rcv(struct sk_buff *skb)
>  		tcp_v6_timewait_ack(sk, skb);
>  		break;
>  	case TCP_TW_RST:
> -		tcp_v6_restore_cb(skb);
>  		tcp_v6_send_reset(sk, skb);
>  		inet_twsk_deschedule_put(inet_twsk(sk));
>  		goto discard_it;
>
>
>
>

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