udp: Generic functions to set checksum

Added udp_set_csum and udp6_set_csum functions to set UDP checksums
in packets. These are for simple UDP packets such as those that might
be created in UDP tunnels.

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 37 insertions, 0 deletions

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index e07d52b8617a..a84f6762ea9e 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -762,6 +762,43 @@ void udp4_hwcsum(struct sk_buff *skb, __be32 src, __be32 dst)
 }
 EXPORT_SYMBOL_GPL(udp4_hwcsum);
 
+/* Function to set UDP checksum for an IPv4 UDP packet. This is intended
+ * for the simple case like when setting the checksum for a UDP tunnel.
+ */
+void udp_set_csum(bool nocheck, struct sk_buff *skb,
+                  __be32 saddr, __be32 daddr, int len)
+{
+        struct udphdr *uh = udp_hdr(skb);
+
+        if (nocheck)
+                uh->check = 0;
+        else if (skb_is_gso(skb))
+                uh->check = ~udp_v4_check(len, saddr, daddr, 0);
+        else if (skb_dst(skb) && skb_dst(skb)->dev &&
+                 (skb_dst(skb)->dev->features & NETIF_F_V4_CSUM)) {
+
+                BUG_ON(skb->ip_summed == CHECKSUM_PARTIAL);
+
+                skb->ip_summed = CHECKSUM_PARTIAL;
+                skb->csum_start = skb_transport_header(skb) - skb->head;
+                skb->csum_offset = offsetof(struct udphdr, check);
+                uh->check = ~udp_v4_check(len, saddr, daddr, 0);
+        } else {
+                __wsum csum;
+
+                BUG_ON(skb->ip_summed == CHECKSUM_PARTIAL);
+
+                uh->check = 0;
+                csum = skb_checksum(skb, 0, len, 0);
+                uh->check = udp_v4_check(len, saddr, daddr, csum);
+                if (uh->check == 0)
+                        uh->check = CSUM_MANGLED_0;
+
+                skb->ip_summed = CHECKSUM_UNNECESSARY;
+        }
+}
+EXPORT_SYMBOL(udp_set_csum);
+
 static int udp_send_skb(struct sk_buff *skb, struct flowi4 *fl4)
 {
         struct sock *sk = skb->sk;