netfilter: conntrack: skip verification of zero UDP checksum

The checksum is optional for UDP packets. However nf_reject would
previously require a valid checksum to elicit a response such as
ICMP_DEST_UNREACH.

Add some logic to nf_reject_verify_csum to determine if a UDP packet has
a zero checksum and should therefore not be verified.

Signed-off-by: Kevin Mitchell <kevmitch@arista.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/include/net/netfilter/nf_reject.h b/include/net/netfilter/nf_reject.h
index 9051c3a0c8e77ce156a2c0f83fbbf369dd72e54b..7c669792fb9ce44ba7581ec3fdfa062c7f5cec01 100644 (file)
--- a/include/net/netfilter/nf_reject.h
+++ b/include/net/netfilter/nf_reject.h
@@ -5,12 +5,28 @@
 #include <linux/types.h>
 #include <uapi/linux/in.h>
 
-static inline bool nf_reject_verify_csum(__u8 proto)
+static inline bool nf_reject_verify_csum(struct sk_buff *skb, int dataoff,
+                                         __u8 proto)
 {
        /* Skip protocols that don't use 16-bit one's complement checksum
         * of the entire payload.
         */
        switch (proto) {
+               /* Protocols with optional checksums. */
+               case IPPROTO_UDP: {
+                       const struct udphdr *udp_hdr;
+                       struct udphdr _udp_hdr;
+
+                       udp_hdr = skb_header_pointer(skb, dataoff,
+                                                    sizeof(_udp_hdr),
+                                                    &_udp_hdr);
+                       if (!udp_hdr || udp_hdr->check)
+                               return true;
+
+                       return false;
+               }
+               case IPPROTO_GRE:
+
                /* Protocols with other integrity checks. */
                case IPPROTO_AH:
                case IPPROTO_ESP:
@@ -19,9 +35,6 @@ static inline bool nf_reject_verify_csum(__u8 proto)
                /* Protocols with partial checksums. */
                case IPPROTO_UDPLITE:
                case IPPROTO_DCCP:
-
-               /* Protocols with optional checksums. */
-               case IPPROTO_GRE:
                        return false;
        }
        return true;

diff --git a/net/ipv4/netfilter/nf_reject_ipv4.c b/net/ipv4/netfilter/nf_reject_ipv4.c
index 4eed5afca392e1bf796d527d23301ca00e3bfed9..918c61fda0f3000fc3e8ccbdb65652dc320c19db 100644 (file)
--- a/net/ipv4/netfilter/nf_reject_ipv4.c
+++ b/net/ipv4/netfilter/nf_reject_ipv4.c
@@ -80,6 +80,7 @@ struct sk_buff *nf_reject_skb_v4_unreach(struct net *net,
        struct iphdr *niph;
        struct icmphdr *icmph;
        unsigned int len;
+       int dataoff;
        __wsum csum;
        u8 proto;
 
@@ -99,10 +100,11 @@ struct sk_buff *nf_reject_skb_v4_unreach(struct net *net,
        if (pskb_trim_rcsum(oldskb, ntohs(ip_hdr(oldskb)->tot_len)))
                return NULL;
 
+       dataoff = ip_hdrlen(oldskb);
        proto = ip_hdr(oldskb)->protocol;
 
        if (!skb_csum_unnecessary(oldskb) &&
-           nf_reject_verify_csum(proto) &&
+           nf_reject_verify_csum(oldskb, dataoff, proto) &&
            nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), proto))
                return NULL;
 
@@ -311,6 +313,7 @@ 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);
+       int dataoff = ip_hdrlen(skb_in);
        u8 proto = iph->protocol;
 
        if (iph->frag_off & htons(IP_OFFSET))
@@ -320,12 +323,13 @@ void nf_send_unreach(struct sk_buff *skb_in, int code, int hook)
            nf_reject_fill_skb_dst(skb_in) < 0)
                return;
 
-       if (skb_csum_unnecessary(skb_in) || !nf_reject_verify_csum(proto)) {
+       if (skb_csum_unnecessary(skb_in) ||
+           !nf_reject_verify_csum(skb_in, dataoff, proto)) {
                icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
                return;
        }
 
-       if (nf_ip_checksum(skb_in, hook, ip_hdrlen(skb_in), proto) == 0)
+       if (nf_ip_checksum(skb_in, hook, dataoff, proto) == 0)
                icmp_send(skb_in, ICMP_DEST_UNREACH, code, 0);
 }
 EXPORT_SYMBOL_GPL(nf_send_unreach);

diff --git a/net/ipv6/netfilter/nf_reject_ipv6.c b/net/ipv6/netfilter/nf_reject_ipv6.c
index dffeaaaadcdedb82ad96cd09cbfa5d88146fab2f..f61d4f18e1cf51d227bf9e6538f120883335c0ff 100644 (file)
--- a/net/ipv6/netfilter/nf_reject_ipv6.c
+++ b/net/ipv6/netfilter/nf_reject_ipv6.c
@@ -31,7 +31,7 @@ static bool nf_reject_v6_csum_ok(struct sk_buff *skb, int hook)
        if (thoff < 0 || thoff >= skb->len || (fo & htons(~0x7)) != 0)
                return false;
 
-       if (!nf_reject_verify_csum(proto))
+       if (!nf_reject_verify_csum(skb, thoff, proto))
                return true;
 
        return nf_ip6_checksum(skb, hook, thoff, proto) == 0;
@@ -388,7 +388,7 @@ static bool reject6_csum_ok(struct sk_buff *skb, int hook)
        if (thoff < 0 || thoff >= skb->len || (fo & htons(~0x7)) != 0)
                return false;
 
-       if (!nf_reject_verify_csum(proto))
+       if (!nf_reject_verify_csum(skb, thoff, proto))
                return true;
 
        return nf_ip6_checksum(skb, hook, thoff, proto) == 0;