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Date: Thu, 22 May 2014 16:06:35 -0400
From: Bandan Das <bsd@...hat.com>
To: David Newall <davidn@...idnewall.com>
Cc: Lukas Tribus <luky-37@...mail.com>,
Eric Dumazet <eric.dumazet@...il.com>,
Netdev <netdev@...r.kernel.org>, "fw\@strlen.de" <fw@...len.de>
Subject: Re: Revert 462fb2af9788a82a534f8184abfde31574e1cfa0 (bridge : Sanitize skb before it enters the IP stack)
David Newall <davidn@...idnewall.com> writes:
> We should revert commit 462fb2af9788a82a534f8184abfde31574e1cfa0
> (bridge : Sanitize skb before it enters the IP stack) because it
> corrupts IP packets with RR or TS options set, only partially updating
> the IP header and leaving an incorrect checksum.
>
> The argument for introducing the change is at lkml.org/lkml/2010/8/30/391:
>
> The bridge layer can overwrite the IPCB using the
> BR_INPUT_SKB_CB macro. In br_nf_dev_queue_xmit,
> if we recieve a packet greater in size than the bridge
> device MTU, we call ip_fragment which in turn will lead to
> icmp_send calling ip_options_echo if the DF flag is set.
> ip_options_echo will then incorrectly try to parse the IPCB as
> IP options resulting in a buffer overflow.
> This change refills the CB area back with IP
> options before ip_fragment calls icmp_send. If we fail parsing,
> we zero out the IPCB area to guarantee that the stack does
> not get corrupted.
>
> A bridge should not fragment packets; an *ethernet* bridge should not
> need to. Fragmenting packets is the job of higher level protocol.
IIRC, older dhcp servers try to set a low enough mtu and that was
causing ip_fragment to bail.. I think I was seeing this with a
KVM guest with a bridged interface set to fetch an ip from the host
network.
Are you sure this won't cause a regression ? I think this was the
relevant change -
static int br_nf_dev_queue_xmit(struct sk_buff *skb)
{
+ int ret;
+
if (skb->nfct != NULL && skb->protocol == htons(ETH_P_IP) &&
skb->len + nf_bridge_mtu_reduction(skb) > skb->dev->mtu &&
!skb_is_gso(skb)) {
- /* BUG: Should really parse the IP options here. */
- memset(IPCB(skb), 0, sizeof(struct inet_skb_parm));
- return ip_fragment(skb, br_dev_queue_push_xmit);
+ if (br_parse_ip_options(skb))
+ /* Drop invalid packet */
+ return NF_DROP;
+ ret = ip_fragment(skb, br_dev_queue_push_xmit);
This call was the reason for the change, are you sure this isn't
applicable anymore ?
} else
- return br_dev_queue_push_xmit(skb);
+ ret = br_dev_queue_push_xmit(skb);
+
+ return ret;
}
> --- br_netfilter.c 2014-01-20 13:10:07.000000000 +1030
> +++ br_netfilter.c.prop 2014-05-16 23:07:57.975386905 +0930
> @@ -253,73 +253,6 @@
> skb->protocol = htons(ETH_P_PPP_SES);
> }
> -/* When handing a packet over to the IP layer
> - * check whether we have a skb that is in the
> - * expected format
> - */
> -
> -static int br_parse_ip_options(struct sk_buff *skb)
> -{
> - struct ip_options *opt;
> - const struct iphdr *iph;
> - struct net_device *dev = skb->dev;
> - u32 len;
> -
> - if (!pskb_may_pull(skb, sizeof(struct iphdr)))
> - goto inhdr_error;
> -
> - iph = ip_hdr(skb);
> - opt = &(IPCB(skb)->opt);
> -
> - /* Basic sanity checks */
> - if (iph->ihl < 5 || iph->version != 4)
> - goto inhdr_error;
> -
> - if (!pskb_may_pull(skb, iph->ihl*4))
> - goto inhdr_error;
> -
> - iph = ip_hdr(skb);
> - if (unlikely(ip_fast_csum((u8 *)iph, iph->ihl)))
> - goto inhdr_error;
> -
> - len = ntohs(iph->tot_len);
> - if (skb->len < len) {
> - IP_INC_STATS_BH(dev_net(dev), IPSTATS_MIB_INTRUNCATEDPKTS);
> - goto drop;
> - } else if (len < (iph->ihl*4))
> - goto inhdr_error;
> -
> - if (pskb_trim_rcsum(skb, len)) {
> - IP_INC_STATS_BH(dev_net(dev), IPSTATS_MIB_INDISCARDS);
> - goto drop;
> - }
> -
> - memset(IPCB(skb), 0, sizeof(struct inet_skb_parm));
> - if (iph->ihl == 5)
> - return 0;
> -
> - opt->optlen = iph->ihl*4 - sizeof(struct iphdr);
> - if (ip_options_compile(dev_net(dev), opt, skb))
> - goto inhdr_error;
> -
> - /* Check correct handling of SRR option */
> - if (unlikely(opt->srr)) {
> - struct in_device *in_dev = __in_dev_get_rcu(dev);
> - if (in_dev && !IN_DEV_SOURCE_ROUTE(in_dev))
> - goto drop;
> -
> - if (ip_options_rcv_srr(skb))
> - goto drop;
> - }
> -
> - return 0;
> -
> -inhdr_error:
> - IP_INC_STATS_BH(dev_net(dev), IPSTATS_MIB_INHDRERRORS);
> -drop:
> - return -1;
> -}
> -
> /* Fill in the header for fragmented IP packets handled by
> * the IPv4 connection tracking code.
> */
> @@ -679,6 +612,7 @@
> {
> struct net_bridge_port *p;
> struct net_bridge *br;
> + const struct iphdr *iph;
> __u32 len = nf_bridge_encap_header_len(skb);
> if (unlikely(!pskb_may_pull(skb, len)))
> @@ -704,9 +638,29 @@
> return NF_ACCEPT;
> nf_bridge_pull_encap_header_rcsum(skb);
> +
> + if (!pskb_may_pull(skb, sizeof(struct iphdr)))
> + goto inhdr_error;
> - if (br_parse_ip_options(skb))
> - return NF_DROP;
> + iph = ip_hdr(skb);
> + if (iph->ihl < 5 || iph->version != 4)
> + goto inhdr_error;
> +
> + if (!pskb_may_pull(skb, 4 * iph->ihl))
> + goto inhdr_error;
> +
> + iph = ip_hdr(skb);
> + if (ip_fast_csum((__u8 *) iph, iph->ihl) != 0)
> + goto inhdr_error;
> +
> + len = ntohs(iph->tot_len);
> + if (skb->len < len || len < 4 * iph->ihl)
> + goto inhdr_error;
> +
> + pskb_trim_rcsum(skb, len);
> +
> + /* BUG: Should really parse the IP options here. */
> + memset(IPCB(skb), 0, sizeof(struct inet_skb_parm));
> nf_bridge_put(skb->nf_bridge);
> if (!nf_bridge_alloc(skb))
> @@ -720,6 +674,10 @@
> br_nf_pre_routing_finish);
> return NF_STOLEN;
> +
> +inhdr_error:
> +// IP_INC_STATS_BH(IpInHdrErrors);
> + return NF_DROP;
> }
> @@ -806,9 +764,6 @@
> nf_bridge->mask |= BRNF_PKT_TYPE;
> }
> - if (pf == NFPROTO_IPV4 && br_parse_ip_options(skb))
> - return NF_DROP;
> -
> /* The physdev module checks on this */
> nf_bridge->mask |= BRNF_BRIDGED;
> nf_bridge->physoutdev = skb->dev;
> @@ -862,19 +817,14 @@
> #if IS_ENABLED(CONFIG_NF_CONNTRACK_IPV4)
> static int br_nf_dev_queue_xmit(struct sk_buff *skb)
> {
> - int ret;
> -
> if (skb->nfct != NULL && skb->protocol == htons(ETH_P_IP) &&
> skb->len + nf_bridge_mtu_reduction(skb) > skb->dev->mtu &&
> !skb_is_gso(skb)) {
> - if (br_parse_ip_options(skb))
> - /* Drop invalid packet */
> - return NF_DROP;
> - ret = ip_fragment(skb, br_dev_queue_push_xmit);
> + /* BUG: Should really parse the IP options here. */
> + memset(IPCB(skb), 0, sizeof(struct inet_skb_parm));
> + return ip_fragment(skb, br_dev_queue_push_xmit);
> } else
> - ret = br_dev_queue_push_xmit(skb);
> -
> - return ret;
> + return br_dev_queue_push_xmit(skb);
> }
> #else
> static int br_nf_dev_queue_xmit(struct sk_buff *skb)
>
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