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Message-ID: <53803488.6000400@davidnewall.com>
Date: Sat, 24 May 2014 15:26:24 +0930
From: David Newall <davidn@...idnewall.com>
To: David Miller <davem@...emloft.net>, bdschuym@...dora.be
CC: fw@...len.de, stephen@...workplumber.org, netdev@...r.kernel.org,
netfilter-devel@...r.kernel.org, bridge@...ts.linux-foundation.org,
Bandan Das <bsd@...hat.com>,
Vlad Yasevich <vyasevich@...il.com>
Subject: Re: Revert 462fb2af9788a82a534f8184abfde31574e1cfa0 (bridge : Sanitize
skb before it enters the IP stack)
On 22/05/14 05:48, David Miller wrote:
> From: Bart De Schuymer<bdschuym@...dora.be>
> Date: Wed, 21 May 2014 20:51:14 +0200
> > There's no reason why they should overlap in the cb: it's 48 bytes
> > big, so big enough to hold both struct br_input_skb_cb and struct
> > inet_skb_parm. The original problem was introduced when
> > BR_INPUT_SKB_CB was introduced (around Feb 27, 2010), so fixing
> > BR_INPUT_SKB_CB seems most appropriate to me.
>
> So you are suggesting the patch below will fix everything?
First, of course I was wrong about ip overflowing the cb area. Even I
thought that was unlikely. I've reread the code, much more carefully,
and spotted where I went wrong.
I've added the change that David Miller provided, to those which I am
proposing, and minimally tested them by pinging through a bridge with RR
set. No surprise: it works.
The patch now reverts the commit and mitigates the original problem by
ensuring bridge's use of cb does not overlap ip's.
--- linux-source-3.13.0/net/bridge/br_netfilter.c.orig 2014-05-17 00:12:23.418906498 +0930
+++ linux-source-3.13.0/net/bridge/br_netfilter.c 2014-05-17 01:04:43.540972961 +0930
@@ -253,73 +253,6 @@ static inline void nf_bridge_update_prot
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 @@ static unsigned int br_nf_pre_routing(co
{
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)))
@@ -704,10 +638,30 @@ static unsigned int br_nf_pre_routing(co
return NF_ACCEPT;
nf_bridge_pull_encap_header_rcsum(skb);
+
+ if (!pskb_may_pull(skb, sizeof(struct iphdr)))
+ return NF_DROP;
- if (br_parse_ip_options(skb))
+ iph = ip_hdr(skb);
+ if (iph->ihl < 5 || iph->version != 4)
+ return NF_DROP;
+
+ if (!pskb_may_pull(skb, 4 * iph->ihl))
return NF_DROP;
+ iph = ip_hdr(skb);
+ if (ip_fast_csum((__u8 *) iph, iph->ihl) != 0)
+ return NF_DROP;
+
+ len = ntohs(iph->tot_len);
+ if (skb->len < len || len < 4 * iph->ihl)
+ return NF_DROP;
+
+ 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))
return NF_DROP;
@@ -806,9 +760,6 @@ static unsigned int br_nf_forward_ip(con
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 +813,14 @@ static unsigned int br_nf_forward_arp(co
#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)
--- linux-source-3.13.0/net/ipv4/ip_options.c.orig 2014-05-16 18:11:10.260370554 +0930
+++ linux-source-3.13.0/net/ipv4/ip_options.c 2014-05-17 01:01:56.738277137 +0930
@@ -475,7 +475,6 @@ error:
}
return -EINVAL;
}
-EXPORT_SYMBOL(ip_options_compile);
/*
* Undo all the changes done by ip_options_compile().
@@ -658,4 +657,3 @@ int ip_options_rcv_srr(struct sk_buff *s
}
return 0;
}
-EXPORT_SYMBOL(ip_options_rcv_srr);
--- /usr/src/linux-source-3.13.0/net/bridge/br_private.h.orig 2014-05-24 13:51:09.269709831 +0930
+++ /usr/src/linux-source-3.13.0/net/bridge/br_private.h 2014-05-24 13:53:20.243551927 +0930
@@ -18,6 +18,7 @@
#include <linux/netpoll.h>
#include <linux/u64_stats_sync.h>
#include <net/route.h>
+#include <net/ip.h>
#include <linux/if_vlan.h>
#define BR_HASH_BITS 8
@@ -304,6 +305,7 @@ struct net_bridge
};
struct br_input_skb_cb {
+ struct inet_skb_parm ip; /* we don't interfere with ip's use of cb area */
struct net_device *brdev;
#ifdef CONFIG_BRIDGE_IGMP_SNOOPING
int igmp;
--
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