The checksum is optional for UDP packets in IPv4. However nf_reject would previously require a valid checksum to illicit 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. Explicitly require a valid checksum for IPv6 consistent RFC 2460 and with the non-netfilter stack (see udp6_csum_zero_error). Signed-off-by: Kevin Mitchell <[email protected]> --- include/net/netfilter/nf_reject.h | 27 ++++++++++++++++++++---- net/bridge/netfilter/nft_reject_bridge.c | 6 ++++-- net/ipv4/netfilter/nf_reject_ipv4.c | 6 ++++-- net/ipv6/netfilter/nf_reject_ipv6.c | 2 +- 4 files changed, 32 insertions(+), 9 deletions(-) diff --git a/include/net/netfilter/nf_reject.h b/include/net/netfilter/nf_reject.h index 9051c3a0c8e7..f248c1ff8b22 100644 --- a/include/net/netfilter/nf_reject.h +++ b/include/net/netfilter/nf_reject.h @@ -5,12 +5,34 @@ #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; + + /* Checksum is required in IPv6 + * see RFC 2460 section 8.1 + */ + if (skb->protocol == htons(ETH_P_IPV6)) + return true; + + 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 +41,6 @@ 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/bridge/netfilter/nft_reject_bridge.c b/net/bridge/netfilter/nft_reject_bridge.c index deae2c9a0f69..e6d62de95378 100644 --- a/net/bridge/netfilter/nft_reject_bridge.c +++ b/net/bridge/netfilter/nft_reject_bridge.c @@ -111,6 +111,7 @@ static void nft_reject_br_send_v4_unreach(struct net *net, unsigned int len; __wsum csum; u8 proto; + int dataoff; if (!nft_bridge_iphdr_validate(oldskb)) return; @@ -129,9 +130,10 @@ static void nft_reject_br_send_v4_unreach(struct net *net, return; proto = ip_hdr(oldskb)->protocol; + dataoff = ip_hdrlen(oldskb); 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; @@ -234,7 +236,7 @@ static bool reject6_br_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; diff --git a/net/ipv4/netfilter/nf_reject_ipv4.c b/net/ipv4/netfilter/nf_reject_ipv4.c index 93b07739807b..7a83fe1c2675 100644 --- a/net/ipv4/netfilter/nf_reject_ipv4.c +++ b/net/ipv4/netfilter/nf_reject_ipv4.c @@ -189,6 +189,7 @@ void nf_send_unreach(struct sk_buff *skb_in, int code, int hook) { struct iphdr *iph = ip_hdr(skb_in); u8 proto = iph->protocol; + int dataoff = ip_hdrlen(skb_in); if (iph->frag_off & htons(IP_OFFSET)) return; @@ -196,12 +197,13 @@ void nf_send_unreach(struct sk_buff *skb_in, int code, int hook) if (hook == NF_INET_PRE_ROUTING && nf_reject_fill_skb_dst(skb_in)) 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 4aef6baaa55e..ac9574c6068f 100644 --- a/net/ipv6/netfilter/nf_reject_ipv6.c +++ b/net/ipv6/netfilter/nf_reject_ipv6.c @@ -253,7 +253,7 @@ 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; -- 2.35.1
