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Message-ID: <ce871ca4-6269-2ae7-bb29-cd2091c6defb@schaufler-ca.com>
Date: Thu, 30 Nov 2017 06:33:17 -0800
From: Casey Schaufler <casey@...aufler-ca.com>
To: Eric Dumazet <eric.dumazet@...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 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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