On Fri, Sep 05, 2008 at 08:49:52AM +0300, Siim Põder wrote:
> Hi
>
> > TCP checksum is not optional, why this change appeared?
>
> The new packets that we handle are on the loopback device and no checksums
> appear to be generated there. I initially changed the condition to check
> for loopback device (which we could do), but checking udp code found that
> it already handled it by checking zero checksum, hence the same
> implementation in tcp code.
I checked with Herbert Xu and its not legal for the checksum to be missing
for TCP. However it is possible for there to be a partial checksum for
loopback traffic. That is, only the pseudo-header is summed.
The patch outlines a fix for this problem using the existing
structure of ip_vs_proto_tcp.c. I believe that a similar fix
is also required for UDP. I am posting it now so people can comment
on its correctness.
Moving forward tcp_partial_csum_update() and tcp_fast_csum_update()
could be implemented in terms of inet_proto_csum_replace* if
inet_proto_csum_replace16 was added. I will work on coding this up.
diff --git a/net/ipv4/ipvs/ip_vs_proto_tcp.c b/net/ipv4/ipvs/ip_vs_proto_tcp.c
index 808e8be..537f616 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);
--
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