From: Matt Corallo <git@bluematt.me>
Date: Sun, 4 Apr 2021 17:14:08 +0000 (-0400)
Subject: Correct second-frag L4 matching
X-Git-Url: http://git.bitcoin.ninja/index.cgi?a=commitdiff_plain;h=b2597a12f3a4c500b43b9888b5174385b0227bc3;p=flowspec-xdp

Correct second-frag L4 matching
---

diff --git a/test.sh b/test.sh
index 10ae086..f13d3f9 100755
--- a/test.sh
+++ b/test.sh
@@ -228,6 +228,17 @@ echo "$TEST_PKT" >> rules.h
 echo "#define TEST_EXP XDP_PASS" >> rules.h
 clang -std=c99 -fsanitize=address -pedantic -Wall -Wextra -Wno-pointer-arith -Wno-unused-variable -O0 -g xdp.c -o xdp && ./xdp
 
+echo "flow6 { src 2620:6e:a007:233::1/128; dst 2001:470:0:503::2/128; fragment !is_fragment || first_fragment || !last_fragment; };" | ./genrules.py --ihl=drop-options --8021q=drop-vlan --v6frag=parse-frags
+echo "$TEST_PKT" >> rules.h
+echo "#define TEST_EXP XDP_PASS" >> rules.h
+clang -std=c99 -fsanitize=address -pedantic -Wall -Wextra -Wno-pointer-arith -Wno-unused-variable -O0 -g xdp.c -o xdp && ./xdp
+
+# Note on the second fragment we don't know the ICMP header (though < 256 is trivially true)
+echo "flow6 { icmp type < 256; };" | ./genrules.py --ihl=drop-options --8021q=drop-vlan --v6frag=parse-frags
+echo "$TEST_PKT" >> rules.h
+echo "#define TEST_EXP XDP_PASS" >> rules.h
+clang -std=c99 -fsanitize=address -pedantic -Wall -Wextra -Wno-pointer-arith -Wno-unused-variable -O0 -g xdp.c -o xdp && ./xdp
+
 #TODO Is nextheader frag correct to match on here? Should we support matching on any nexthdr?
 echo "flow6 { next header 44; };" | ./genrules.py --ihl=accept-options --8021q=accept-vlan --v6frag=parse-frags
 echo "$TEST_PKT" >> rules.h
diff --git a/xdp.c b/xdp.c
index 1709e00..74e8e8c 100644
--- a/xdp.c
+++ b/xdp.c
@@ -226,18 +226,20 @@ int xdp_drop_prog(struct xdp_md *ctx)
 		l4hdr = pktdata + 5*4;
 #endif
 
-		if (ip->protocol == IP_PROTO_TCP) {
-			if (unlikely(l4hdr + sizeof(struct tcphdr) > data_end))
-				DO_RETURN(PKT_LEN_DROP, XDP_DROP);
-			tcp = (struct tcphdr*) l4hdr;
-		} else if (ip->protocol == IP_PROTO_UDP) {
-			if (unlikely(l4hdr + sizeof(struct udphdr) > data_end))
-				DO_RETURN(PKT_LEN_DROP, XDP_DROP);
-			udp = (struct udphdr*) l4hdr;
-		} else if (ip->protocol == IP_PROTO_ICMP) {
-			if (unlikely(l4hdr + sizeof(struct icmphdr) > data_end))
-				DO_RETURN(PKT_LEN_DROP, XDP_DROP);
-			icmp = (struct icmphdr*) l4hdr;
+		if ((ip->frag_off & BE16(IP_OFFSET)) == 0) {
+			if (ip->protocol == IP_PROTO_TCP) {
+				if (unlikely(l4hdr + sizeof(struct tcphdr) > data_end))
+					DO_RETURN(PKT_LEN_DROP, XDP_DROP);
+				tcp = (struct tcphdr*) l4hdr;
+			} else if (ip->protocol == IP_PROTO_UDP) {
+				if (unlikely(l4hdr + sizeof(struct udphdr) > data_end))
+					DO_RETURN(PKT_LEN_DROP, XDP_DROP);
+				udp = (struct udphdr*) l4hdr;
+			} else if (ip->protocol == IP_PROTO_ICMP) {
+				if (unlikely(l4hdr + sizeof(struct icmphdr) > data_end))
+					DO_RETURN(PKT_LEN_DROP, XDP_DROP);
+				icmp = (struct icmphdr*) l4hdr;
+			}
 		}
 	}
 #endif
@@ -264,21 +266,23 @@ int xdp_drop_prog(struct xdp_md *ctx)
 #endif
 		}
 #endif
-
-		if (v6nexthdr == IP_PROTO_TCP) {
-			if (unlikely(l4hdr + sizeof(struct tcphdr) > data_end))
-				DO_RETURN(PKT_LEN_DROP, XDP_DROP);
-			tcp = (struct tcphdr*) l4hdr;
-		} else if (v6nexthdr == IP_PROTO_UDP) {
-			if (unlikely(l4hdr + sizeof(struct udphdr) > data_end))
-				DO_RETURN(PKT_LEN_DROP, XDP_DROP);
-			udp = (struct udphdr*) l4hdr;
-		} else if (v6nexthdr == IP6_PROTO_ICMPV6) {
-			if (unlikely(l4hdr + sizeof(struct icmp6hdr) > data_end))
-				DO_RETURN(PKT_LEN_DROP, XDP_DROP);
-			icmpv6 = (struct icmp6hdr*) l4hdr;
+		// TODO: Handle more options?
+
+		if (frag6 == NULL || (frag6->frag_off & BE16(IP6_FRAGOFF)) == 0) {
+			if (v6nexthdr == IP_PROTO_TCP) {
+				if (unlikely(l4hdr + sizeof(struct tcphdr) > data_end))
+					DO_RETURN(PKT_LEN_DROP, XDP_DROP);
+				tcp = (struct tcphdr*) l4hdr;
+			} else if (v6nexthdr == IP_PROTO_UDP) {
+				if (unlikely(l4hdr + sizeof(struct udphdr) > data_end))
+					DO_RETURN(PKT_LEN_DROP, XDP_DROP);
+				udp = (struct udphdr*) l4hdr;
+			} else if (v6nexthdr == IP6_PROTO_ICMPV6) {
+				if (unlikely(l4hdr + sizeof(struct icmp6hdr) > data_end))
+					DO_RETURN(PKT_LEN_DROP, XDP_DROP);
+				icmpv6 = (struct icmp6hdr*) l4hdr;
+			}
 		}
-		// TODO: Handle some options?
 	}
 #endif