From: Matt Corallo Date: Sun, 4 Apr 2021 18:19:06 +0000 (-0400) Subject: Clean up length checks with a macro and comment strange semantics X-Git-Url: http://git.bitcoin.ninja/index.cgi?a=commitdiff_plain;h=d6b7fc49f9d67897d77f2db7caa3ec6628513ffe;p=flowspec-xdp Clean up length checks with a macro and comment strange semantics --- diff --git a/xdp.c b/xdp.c index 74e8e8c..fc2198d 100644 --- a/xdp.c +++ b/xdp.c @@ -159,6 +159,12 @@ struct bpf_map_def SEC("maps") drop_cnt_map = { SEC("xdp_drop") #endif + +// It seems (based on drop counts) that data_end points to the last byte, not one-past-the-end. +// This feels strange, but some documentation suggests > here as well, so we stick with that. +#define CHECK_LEN(start, struc) \ + if (unlikely((void*)(start) + sizeof(struct struc) > data_end)) DO_RETURN(PKT_LEN_DROP, XDP_DROP); + int xdp_drop_prog(struct xdp_md *ctx) { const void *const data_end = (void *)(size_t)ctx->data_end; @@ -167,14 +173,12 @@ int xdp_drop_prog(struct xdp_md *ctx) unsigned short eth_proto; { - if (unlikely((void*)(size_t)ctx->data + sizeof(struct ethhdr) > data_end)) - DO_RETURN(PKT_LEN_DROP, XDP_DROP); + CHECK_LEN((size_t)ctx->data, ethhdr); const struct ethhdr *const eth = (void*)(size_t)ctx->data; #if PARSE_8021Q == PARSE if (likely(eth->h_proto == BE16(ETH_P_8021Q))) { - if (unlikely((void*)(size_t)ctx->data + sizeof(struct ethhdr_vlan) > data_end)) - DO_RETURN(PKT_LEN_DROP, XDP_DROP); + CHECK_LEN((size_t)ctx->data, ethhdr_vlan); const struct ethhdr_vlan *const eth_vlan = (void*)(size_t)ctx->data; #ifdef REQ_8021Q @@ -214,8 +218,7 @@ int xdp_drop_prog(struct xdp_md *ctx) #ifdef NEED_V4_PARSE if (eth_proto == BE16(ETH_P_IP)) { - if (unlikely(pktdata + sizeof(struct iphdr) > data_end)) - DO_RETURN(PKT_LEN_DROP, XDP_DROP); + CHECK_LEN(pktdata, iphdr); ip = (struct iphdr*) pktdata; #if PARSE_IHL == PARSE @@ -228,16 +231,13 @@ int xdp_drop_prog(struct xdp_md *ctx) 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); + CHECK_LEN(l4hdr, tcphdr); 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); + CHECK_LEN(l4hdr, udphdr); 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); + CHECK_LEN(l4hdr, icmphdr); icmp = (struct icmphdr*) l4hdr; } } @@ -245,8 +245,7 @@ int xdp_drop_prog(struct xdp_md *ctx) #endif #ifdef NEED_V6_PARSE if (eth_proto == BE16(ETH_P_IPV6)) { - if (unlikely(pktdata + sizeof(struct ip6hdr) > data_end)) - DO_RETURN(PKT_LEN_DROP, XDP_DROP); + CHECK_LEN(pktdata, ip6hdr); ip6 = (struct ip6hdr*) pktdata; l4hdr = pktdata + 40; @@ -255,8 +254,7 @@ int xdp_drop_prog(struct xdp_md *ctx) #ifdef PARSE_V6_FRAG #if PARSE_V6_FRAG == PARSE if (ip6->nexthdr == IP6_PROTO_FRAG) { - if (unlikely(l4hdr + sizeof(struct ip6_fraghdr) > data_end)) - DO_RETURN(PKT_LEN_DROP, XDP_DROP); + CHECK_LEN(l4hdr, ip6_fraghdr); frag6 = (struct ip6_fraghdr*) l4hdr; l4hdr = l4hdr + sizeof(struct ip6_fraghdr); v6nexthdr = frag6->nexthdr; @@ -270,16 +268,13 @@ int xdp_drop_prog(struct xdp_md *ctx) 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); + CHECK_LEN(l4hdr, tcphdr); 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); + CHECK_LEN(l4hdr, udphdr); 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); + CHECK_LEN(l4hdr, icmp6hdr); icmpv6 = (struct icmp6hdr*) l4hdr; } }