clatd: Use the TUN_NOCHECKSUM flag for the tun device

This is needed to handle cases when the packet socket receives
a GRO coalesced packet which will not have a valid TCP checksum.
TUN_NOCHECKSUM is used only when the checksum has already been
verified prior to this and GRO is being used.

Change-Id: I1409967523152bb7620b4881526e78e8c222cc72

4 files changed, 77 insertions, 0 deletions

diff --git a/clatd.c b/clatd.c
index faeb679..ca21984 100644
--- a/clatd.c
+++ b/clatd.c
@@ -496,6 +496,9 @@ int main(int argc, char **argv) {
   // run under a regular user
   drop_root();
 
+  //check HW features and disable checksum validation if already handled by hardware
+  rx_checksum_offloaded = check_csum_offload(uplink_interface);
+
   // we can create tun devices as non-root because we're in the VPN group.
   tunnel.fd4 = tun_open();
   if(tunnel.fd4 < 0) {
diff --git a/config.h b/config.h
index e31a81d..82a91be 100644
--- a/config.h
+++ b/config.h
@@ -39,6 +39,8 @@ struct clat_config {
 
 extern struct clat_config Global_Clatd_Config;
 
+extern int rx_checksum_offloaded;
+
 int read_config(const char *file, const char *uplink_interface, const char *plat_prefix,
         unsigned net_id);
 void config_generate_local_ipv6_subnet(struct in6_addr *interface_ip);
diff --git a/tun.c b/tun.c
index 49f0ea7..8068b2f 100644
--- a/tun.c
+++ b/tun.c
@@ -22,10 +22,14 @@
 #include <linux/if.h>
 #include <linux/if_tun.h>
 #include <sys/ioctl.h>
+#include <linux/ethtool.h>
 #include <sys/uio.h>
 
+#include "config.h"
 #include "clatd.h"
 
+int rx_checksum_offloaded = 0;
+
 /* function: tun_open
  * tries to open the tunnel device
  */
@@ -61,6 +65,11 @@ int tun_alloc(char *dev, int fd) {
     return err;
   }
   strcpy(dev, ifr.ifr_name);
+
+  if (rx_checksum_offloaded) {
+    ioctl(fd, TUNSETNOCSUM, 1);
+  }
+
   return 0;
 }
 
@@ -87,3 +96,65 @@ int set_nonblocking(int fd) {
 int send_tun(int fd, clat_packet out, int iov_len) {
   return writev(fd, out, iov_len);
 }
+
+/* function: get_ethtool_feature_val
+ * gets if a particular ethtool feature is enabled
+ * dev     - the device name to query the feature on
+ * cmd     - the feature to query
+ * returns: 1 if feature is enabled, 0 if disabled
+ */
+int get_ethtool_feature_val(char *dev, int cmd) {
+  int fd;
+  struct ifreq ifr;
+  struct ethtool_value eval;
+
+  if (!dev){
+    return 0;
+  }
+
+  if((fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0 ) {
+    return 0;
+  }
+
+  memset(&ifr, 0, sizeof(ifr));
+  memset(&eval, 0, sizeof(eval));
+  strlcpy(ifr.ifr_name, dev, sizeof(ifr.ifr_name));
+  eval.cmd = cmd;
+  eval.data = 0;
+  ifr.ifr_data = (caddr_t)&eval;
+  if (ioctl(fd, SIOCETHTOOL, &ifr) == -1) {
+      close(fd);
+      return 0;
+  }
+
+  close(fd);
+
+  if (!eval.data) {
+    return 0;
+  }
+
+  return 1;
+}
+
+/* function: check_csum_offload
+ * checks if GRO and RXCSUM are enabled on the device
+ * dev     - the device name to query on
+ * returns: 1 if checksum is offloaded, 0 if checksum needs
+ *          to be validated in network stack.
+ */
+int check_csum_offload(char *dev) {
+  int fd;
+  struct ifreq ifr;
+  struct ethtool_value eval;
+
+  if (!dev){
+    return 0;
+  }
+
+  if(get_ethtool_feature_val(dev, ETHTOOL_GGRO) &&
+     get_ethtool_feature_val(dev, ETHTOOL_GRXCSUM)) {
+    return 1;
+  }
+
+  return 0;
+}
diff --git a/tun.h b/tun.h
index bcdd10e..f1c41bf 100644
--- a/tun.h
+++ b/tun.h
@@ -33,5 +33,6 @@ int tun_open();
 int tun_alloc(char *dev, int fd);
 int send_tun(int fd, clat_packet out, int iov_len);
 int set_nonblocking(int fd);
+int check_csum_offload(char *dev);
 
 #endif