ipvs: handle PARTIAL_CHECKSUM

Now that LVS can load balance locally generated traffic, packets may come
from the loopback device and thus may have a partial checksum.

The existing code allows for the case where there is no checksum at all for
TCP, however Herbert Xu has confirmed that this is not legal.

Signed-off-by: Simon Horman <horms@verge.net.au>
Acked-by: Julius Volz <juliusv@google.com>

2 files changed, 70 insertions, 4 deletions

diff --git a/net/ipv4/ipvs/ip_vs_proto_tcp.c b/net/ipv4/ipvs/ip_vs_proto_tcp.c
index 808e8be0280a..537f616776da 100644
--- a/net/ipv4/ipvs/ip_vs_proto_tcp.c
+++ b/net/ipv4/ipvs/ip_vs_proto_tcp.c
@@ -134,12 +134,34 @@ tcp_fast_csum_update(int af, struct tcphdr *tcph,
 }
 
 
+static inline void
+tcp_partial_csum_update(int af, struct tcphdr *tcph,
+                     const union nf_inet_addr *oldip,
+                     const union nf_inet_addr *newip,
+                     __be16 oldlen, __be16 newlen)
+{
+#ifdef CONFIG_IP_VS_IPV6
+        if (af == AF_INET6)
+                tcph->check =
+                        csum_fold(ip_vs_check_diff16(oldip->ip6, newip->ip6,
+                                         ip_vs_check_diff2(oldlen, newlen,
+                                                ~csum_unfold(tcph->check))));
+        else
+#endif
+        tcph->check =
+                csum_fold(ip_vs_check_diff4(oldip->ip, newip->ip,
+                                ip_vs_check_diff2(oldlen, newlen,
+                                                ~csum_unfold(tcph->check))));
+}
+
+
 static int
 tcp_snat_handler(struct sk_buff *skb,
                  struct ip_vs_protocol *pp, struct ip_vs_conn *cp)
 {
         struct tcphdr *tcph;
         unsigned int tcphoff;
+        int oldlen;
 
 #ifdef CONFIG_IP_VS_IPV6
         if (cp->af == AF_INET6)
@@ -147,6 +169,7 @@ tcp_snat_handler(struct sk_buff *skb,
         else
 #endif
                 tcphoff = ip_hdrlen(skb);
+        oldlen = skb->len - tcphoff;
 
         /* csum_check requires unshared skb */
         if (!skb_make_writable(skb, tcphoff+sizeof(*tcph)))
@@ -166,7 +189,11 @@ tcp_snat_handler(struct sk_buff *skb,
         tcph->source = cp->vport;
 
         /* Adjust TCP checksums */
-        if (!cp->app && (tcph->check != 0)) {
+        if (skb->ip_summed == CHECKSUM_PARTIAL) {
+                tcp_partial_csum_update(cp->af, tcph, &cp->daddr, &cp->vaddr,
+                                        htonl(oldlen),
+                                        htonl(skb->len - tcphoff));
+        } else if (!cp->app) {
                 /* Only port and addr are changed, do fast csum update */
                 tcp_fast_csum_update(cp->af, tcph, &cp->daddr, &cp->vaddr,
                                      cp->dport, cp->vport);
@@ -204,6 +231,7 @@ tcp_dnat_handler(struct sk_buff *skb,
 {
         struct tcphdr *tcph;
         unsigned int tcphoff;
+        int oldlen;
 
 #ifdef CONFIG_IP_VS_IPV6
         if (cp->af == AF_INET6)
@@ -211,6 +239,7 @@ tcp_dnat_handler(struct sk_buff *skb,
         else
 #endif
                 tcphoff = ip_hdrlen(skb);
+        oldlen = skb->len - tcphoff;
 
         /* csum_check requires unshared skb */
         if (!skb_make_writable(skb, tcphoff+sizeof(*tcph)))
@@ -235,7 +264,11 @@ tcp_dnat_handler(struct sk_buff *skb,
         /*
          *      Adjust TCP checksums
          */
-        if (!cp->app && (tcph->check != 0)) {
+        if (skb->ip_summed == CHECKSUM_PARTIAL) {
+                tcp_partial_csum_update(cp->af, tcph, &cp->daddr, &cp->vaddr,
+                                        htonl(oldlen),
+                                        htonl(skb->len - tcphoff));
+        } else if (!cp->app) {
                 /* Only port and addr are changed, do fast csum update */
                 tcp_fast_csum_update(cp->af, tcph, &cp->vaddr, &cp->daddr,
                                      cp->vport, cp->dport);
diff --git a/net/ipv4/ipvs/ip_vs_proto_udp.c b/net/ipv4/ipvs/ip_vs_proto_udp.c
index 5f2073e41cf6..e3ee26bd1de7 100644
--- a/net/ipv4/ipvs/ip_vs_proto_udp.c
+++ b/net/ipv4/ipvs/ip_vs_proto_udp.c
@@ -141,12 +141,34 @@ udp_fast_csum_update(int af, struct udphdr *uhdr,
                 uhdr->check = CSUM_MANGLED_0;
 }
 
+static inline void
+udp_partial_csum_update(int af, struct udphdr *uhdr,
+                     const union nf_inet_addr *oldip,
+                     const union nf_inet_addr *newip,
+                     __be16 oldlen, __be16 newlen)
+{
+#ifdef CONFIG_IP_VS_IPV6
+        if (af == AF_INET6)
+                uhdr->check =
+                        csum_fold(ip_vs_check_diff16(oldip->ip6, newip->ip6,
+                                         ip_vs_check_diff2(oldlen, newlen,
+                                                ~csum_unfold(uhdr->check))));
+        else
+#endif
+        uhdr->check =
+                csum_fold(ip_vs_check_diff4(oldip->ip, newip->ip,
+                                ip_vs_check_diff2(oldlen, newlen,
+                                                ~csum_unfold(uhdr->check))));
+}
+
+
 static int
 udp_snat_handler(struct sk_buff *skb,
                  struct ip_vs_protocol *pp, struct ip_vs_conn *cp)
 {
         struct udphdr *udph;
         unsigned int udphoff;
+        int oldlen;
 
 #ifdef CONFIG_IP_VS_IPV6
         if (cp->af == AF_INET6)
@@ -154,6 +176,7 @@ udp_snat_handler(struct sk_buff *skb,
         else
 #endif
                 udphoff = ip_hdrlen(skb);
+        oldlen = skb->len - udphoff;
 
         /* csum_check requires unshared skb */
         if (!skb_make_writable(skb, udphoff+sizeof(*udph)))
@@ -177,7 +200,11 @@ udp_snat_handler(struct sk_buff *skb,
         /*
          *      Adjust UDP checksums
          */
-        if (!cp->app && (udph->check != 0)) {
+        if (skb->ip_summed == CHECKSUM_PARTIAL) {
+                udp_partial_csum_update(cp->af, udph, &cp->daddr, &cp->vaddr,
+                                        htonl(oldlen),
+                                        htonl(skb->len - udphoff));
+        } else if (!cp->app && (udph->check != 0)) {
                 /* Only port and addr are changed, do fast csum update */
                 udp_fast_csum_update(cp->af, udph, &cp->daddr, &cp->vaddr,
                                      cp->dport, cp->vport);
@@ -216,6 +243,7 @@ udp_dnat_handler(struct sk_buff *skb,
 {
         struct udphdr *udph;
         unsigned int udphoff;
+        int oldlen;
 
 #ifdef CONFIG_IP_VS_IPV6
         if (cp->af == AF_INET6)
@@ -223,6 +251,7 @@ udp_dnat_handler(struct sk_buff *skb,
         else
 #endif
                 udphoff = ip_hdrlen(skb);
+        oldlen = skb->len - udphoff;
 
         /* csum_check requires unshared skb */
         if (!skb_make_writable(skb, udphoff+sizeof(*udph)))
@@ -247,7 +276,11 @@ udp_dnat_handler(struct sk_buff *skb,
         /*
          *      Adjust UDP checksums
          */
-        if (!cp->app && (udph->check != 0)) {
+        if (skb->ip_summed == CHECKSUM_PARTIAL) {
+                udp_partial_csum_update(cp->af, udph, &cp->daddr, &cp->vaddr,
+                                        htonl(oldlen),
+                                        htonl(skb->len - udphoff));
+        } else if (!cp->app && (udph->check != 0)) {
                 /* Only port and addr are changed, do fast csum update */
                 udp_fast_csum_update(cp->af, udph, &cp->vaddr, &cp->daddr,
                                      cp->vport, cp->dport);