netfilter: reject: don't send icmp error if csum is invalid

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.

Validate csum if needed and only send the response if it is ok.

Reference: http://bugzilla.redhat.com/show_bug.cgi?id=1169829
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/include/net/netfilter/ipv4/nf_reject.h b/include/net/netfilter/ipv4/nf_reject.h
index 03e928a..8641275 100644 (file)
--- 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 (file)
--- 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 (file)
--- 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..b7405eb 100644 (file)
--- a/net/ipv4/netfilter/nf_reject_ipv4.c
+++ b/net/ipv4/netfilter/nf_reject_ipv4.c
@@ -164,4 +164,27 @@ 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);
+       u8 proto;
+
+       if (skb_in->csum_bad || iph->frag_off & htons(IP_OFFSET))
+               return;
+
+       if (skb_csum_unnecessary(skb_in)) {
+               icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
+               return;
+       }
+
+       if (iph->protocol == IPPROTO_TCP || iph->protocol == IPPROTO_UDP)
+               proto = iph->protocol;
+       else
+               proto = 0;
+
+       if (nf_ip_checksum(skb_in, hook, ip_hdrlen(skb_in), proto) == 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 (file)
--- 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..68e0bb4 100644 (file)
--- a/net/ipv6/netfilter/nf_reject_ipv6.c
+++ b/net/ipv6/netfilter/nf_reject_ipv6.c
@@ -208,4 +208,39 @@ 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;
+
+       if (skb->csum_bad)
+               return false;
+
+       if (skb_csum_unnecessary(skb))
+               return true;
+
+       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 (file)
--- 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;