tcp resets are never emitted if the packet that triggers the
reject/reset has an invalid checksum.
For icmp error responses there was no such check.
It allows to distinguish icmp response generated via
iptables -I INPUT -p udp --dport 42 -j REJECT
and those emitted by network stack (won't respond if csum is invalid,
REJECT does).
Arguably its possible to avoid this by using conntrack and only
using REJECT with -m conntrack NEW/RELATED.
However, this doesn't work when connection tracking is not in use
or when using nf_conntrack_checksum=0.
Furthermore, sending errors in response to invalid csums doesn't make
much sense so just add similar test as in nf_send_reset.
Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
---
v2: bail if thoff exceeds skb->len.
Otherwise no changes.
Sending this for discussion only; see my discussion wrt. UDPLITE and SCTP
checksum validation; its currently untested/unsolved issue.
Furthermore I'm away for next days (reachable by email) so please
don't apply this just yet.
include/net/netfilter/ipv4/nf_reject.h | 6 +-----
include/net/netfilter/ipv6/nf_reject.h | 11 ++---------
net/ipv4/netfilter/ipt_REJECT.c | 17 +++++++++--------
net/ipv4/netfilter/nf_reject_ipv4.c | 12 ++++++++++++
net/ipv4/netfilter/nft_reject_ipv4.c | 3 ++-
net/ipv6/netfilter/nf_reject_ipv6.c | 29 +++++++++++++++++++++++++++++
net/netfilter/nft_reject_inet.c | 6 ++++--
7 files changed, 59 insertions(+), 25 deletions(-)
diff --git a/include/net/netfilter/ipv4/nf_reject.h b/include/net/netfilter/ipv4/nf_reject.h
index 03e928a..8641275 100644
--- a/include/net/netfilter/ipv4/nf_reject.h
+++ b/include/net/netfilter/ipv4/nf_reject.h
@@ -5,11 +5,7 @@
#include <net/ip.h>
#include <net/icmp.h>
-static inline void nf_send_unreach(struct sk_buff *skb_in, int code)
-{
- icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
-}
-
+void nf_send_unreach(struct sk_buff *skb_in, int code, int hook);
void nf_send_reset(struct sk_buff *oldskb, int hook);
const struct tcphdr *nf_reject_ip_tcphdr_get(struct sk_buff *oldskb,
diff --git a/include/net/netfilter/ipv6/nf_reject.h b/include/net/netfilter/ipv6/nf_reject.h
index 23216d4..0ae445d 100644
--- a/include/net/netfilter/ipv6/nf_reject.h
+++ b/include/net/netfilter/ipv6/nf_reject.h
@@ -3,15 +3,8 @@
#include <linux/icmpv6.h>
-static inline void
-nf_send_unreach6(struct net *net, struct sk_buff *skb_in, unsigned char code,
- unsigned int hooknum)
-{
- if (hooknum == NF_INET_LOCAL_OUT && skb_in->dev == NULL)
- skb_in->dev = net->loopback_dev;
-
- icmpv6_send(skb_in, ICMPV6_DEST_UNREACH, code, 0);
-}
+void nf_send_unreach6(struct net *net, struct sk_buff *skb_in, unsigned char code,
+ unsigned int hooknum);
void nf_send_reset6(struct net *net, struct sk_buff *oldskb, int hook);
diff --git a/net/ipv4/netfilter/ipt_REJECT.c b/net/ipv4/netfilter/ipt_REJECT.c
index 8f48f55..87907d4 100644
--- a/net/ipv4/netfilter/ipt_REJECT.c
+++ b/net/ipv4/netfilter/ipt_REJECT.c
@@ -34,31 +34,32 @@ static unsigned int
reject_tg(struct sk_buff *skb, const struct xt_action_param *par)
{
const struct ipt_reject_info *reject = par->targinfo;
+ int hook = par->hooknum;
switch (reject->with) {
case IPT_ICMP_NET_UNREACHABLE:
- nf_send_unreach(skb, ICMP_NET_UNREACH);
+ nf_send_unreach(skb, ICMP_NET_UNREACH, hook);
break;
case IPT_ICMP_HOST_UNREACHABLE:
- nf_send_unreach(skb, ICMP_HOST_UNREACH);
+ nf_send_unreach(skb, ICMP_HOST_UNREACH, hook);
break;
case IPT_ICMP_PROT_UNREACHABLE:
- nf_send_unreach(skb, ICMP_PROT_UNREACH);
+ nf_send_unreach(skb, ICMP_PROT_UNREACH, hook);
break;
case IPT_ICMP_PORT_UNREACHABLE:
- nf_send_unreach(skb, ICMP_PORT_UNREACH);
+ nf_send_unreach(skb, ICMP_PORT_UNREACH, hook);
break;
case IPT_ICMP_NET_PROHIBITED:
- nf_send_unreach(skb, ICMP_NET_ANO);
+ nf_send_unreach(skb, ICMP_NET_ANO, hook);
break;
case IPT_ICMP_HOST_PROHIBITED:
- nf_send_unreach(skb, ICMP_HOST_ANO);
+ nf_send_unreach(skb, ICMP_HOST_ANO, hook);
break;
case IPT_ICMP_ADMIN_PROHIBITED:
- nf_send_unreach(skb, ICMP_PKT_FILTERED);
+ nf_send_unreach(skb, ICMP_PKT_FILTERED, hook);
break;
case IPT_TCP_RESET:
- nf_send_reset(skb, par->hooknum);
+ nf_send_reset(skb, hook);
case IPT_ICMP_ECHOREPLY:
/* Doesn't happen. */
break;
diff --git a/net/ipv4/netfilter/nf_reject_ipv4.c b/net/ipv4/netfilter/nf_reject_ipv4.c
index 536da7b..b3e50c8 100644
--- a/net/ipv4/netfilter/nf_reject_ipv4.c
+++ b/net/ipv4/netfilter/nf_reject_ipv4.c
@@ -164,4 +164,16 @@ void nf_send_reset(struct sk_buff *oldskb, int hook)
}
EXPORT_SYMBOL_GPL(nf_send_reset);
+void nf_send_unreach(struct sk_buff *skb_in, int code, int hook)
+{
+ struct iphdr *iph = ip_hdr(skb_in);
+
+ if (iph->frag_off & htons(IP_OFFSET))
+ return;
+
+ if (nf_ip_checksum(skb_in, hook, ip_hdrlen(skb_in), iph->protocol) == 0)
+ icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
+}
+EXPORT_SYMBOL_GPL(nf_send_unreach);
+
MODULE_LICENSE("GPL");
diff --git a/net/ipv4/netfilter/nft_reject_ipv4.c b/net/ipv4/netfilter/nft_reject_ipv4.c
index d729542..16a5d4d 100644
--- a/net/ipv4/netfilter/nft_reject_ipv4.c
+++ b/net/ipv4/netfilter/nft_reject_ipv4.c
@@ -27,7 +27,8 @@ static void nft_reject_ipv4_eval(const struct nft_expr *expr,
switch (priv->type) {
case NFT_REJECT_ICMP_UNREACH:
- nf_send_unreach(pkt->skb, priv->icmp_code);
+ nf_send_unreach(pkt->skb, priv->icmp_code,
+ pkt->ops->hooknum);
break;
case NFT_REJECT_TCP_RST:
nf_send_reset(pkt->skb, pkt->ops->hooknum);
diff --git a/net/ipv6/netfilter/nf_reject_ipv6.c b/net/ipv6/netfilter/nf_reject_ipv6.c
index d05b364..7496850 100644
--- a/net/ipv6/netfilter/nf_reject_ipv6.c
+++ b/net/ipv6/netfilter/nf_reject_ipv6.c
@@ -208,4 +208,33 @@ void nf_send_reset6(struct net *net, struct sk_buff *oldskb, int hook)
}
EXPORT_SYMBOL_GPL(nf_send_reset6);
+static bool reject6_csum_ok(struct sk_buff *skb, int hook)
+{
+ const struct ipv6hdr *ip6h = ipv6_hdr(skb);
+ int thoff;
+ __be16 fo;
+ u8 proto;
+
+ proto = ip6h->nexthdr;
+ thoff = ipv6_skip_exthdr(skb, ((u8*)(ip6h+1) - skb->data), &proto, &fo);
+
+ if (thoff < 0 || thoff >= skb->len || (fo & htons(~0x7)) != 0)
+ return false;
+
+ return nf_ip6_checksum(skb, hook, thoff, proto) == 0;
+}
+
+void nf_send_unreach6(struct net *net, struct sk_buff *skb_in,
+ unsigned char code, unsigned int hooknum)
+{
+ if (!reject6_csum_ok(skb_in, hooknum))
+ return;
+
+ if (hooknum == NF_INET_LOCAL_OUT && skb_in->dev == NULL)
+ skb_in->dev = net->loopback_dev;
+
+ icmpv6_send(skb_in, ICMPV6_DEST_UNREACH, code, 0);
+}
+EXPORT_SYMBOL_GPL(nf_send_unreach6);
+
MODULE_LICENSE("GPL");
diff --git a/net/netfilter/nft_reject_inet.c b/net/netfilter/nft_reject_inet.c
index 7b5f9d5..9287711 100644
--- a/net/netfilter/nft_reject_inet.c
+++ b/net/netfilter/nft_reject_inet.c
@@ -28,14 +28,16 @@ static void nft_reject_inet_eval(const struct nft_expr *expr,
case NFPROTO_IPV4:
switch (priv->type) {
case NFT_REJECT_ICMP_UNREACH:
- nf_send_unreach(pkt->skb, priv->icmp_code);
+ nf_send_unreach(pkt->skb, priv->icmp_code,
+ pkt->ops->hooknum);
break;
case NFT_REJECT_TCP_RST:
nf_send_reset(pkt->skb, pkt->ops->hooknum);
break;
case NFT_REJECT_ICMPX_UNREACH:
nf_send_unreach(pkt->skb,
- nft_reject_icmp_code(priv->icmp_code));
+ nft_reject_icmp_code(priv->icmp_code),
+ pkt->ops->hooknum);
break;
}
break;
--
2.0.5
--
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