net: tun: convert to hw_features

This changes offload setting behaviour to what I think is correct:
 - offloads set via ethtool mean what admin wants to use (by default
   he wants 'em all)
 - offloads set via ioctl() mean what userspace is expecting to get
   (this limits which admin wishes are granted)
 - TUN_NOCHECKSUM is ignored, as it might cause broken packets when
   forwarded (ip_summed == CHECKSUM_UNNECESSARY means that checksum
   was verified, not that it can be ignored)

If TUN_NOCHECKSUM is implemented, it should set skb->csum_* and
skb->ip_summed (= CHECKSUM_PARTIAL) for known protocols and let others
be verified by kernel when necessary.

TUN_NOCHECKSUM handling was introduced by commit
f43798c27684ab925adde7d8acc34c78c6e50df8:

    tun: Allow GSO using virtio_net_hdr

Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 25 insertions, 38 deletions

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index f5e9ac00a07b..ade3cf9cd326 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -123,6 +123,9 @@ struct tun_struct {
         gid_t                   group;
 
         struct net_device       *dev;
+        u32                     set_features;
+#define TUN_USER_FEATURES (NETIF_F_HW_CSUM|NETIF_F_TSO_ECN|NETIF_F_TSO| \
+                          NETIF_F_TSO6|NETIF_F_UFO)
         struct fasync_struct    *fasync;
 
         struct tap_filter       txflt;
@@ -451,12 +454,20 @@ tun_net_change_mtu(struct net_device *dev, int new_mtu)
         return 0;
 }
 
+static u32 tun_net_fix_features(struct net_device *dev, u32 features)
+{
+        struct tun_struct *tun = netdev_priv(dev);
+
+        return (features & tun->set_features) | (features & ~TUN_USER_FEATURES);
+}
+
 static const struct net_device_ops tun_netdev_ops = {
         .ndo_uninit             = tun_net_uninit,
         .ndo_open               = tun_net_open,
         .ndo_stop               = tun_net_close,
         .ndo_start_xmit         = tun_net_xmit,
         .ndo_change_mtu         = tun_net_change_mtu,
+        .ndo_fix_features       = tun_net_fix_features,
 };
 
 static const struct net_device_ops tap_netdev_ops = {
@@ -465,6 +476,7 @@ static const struct net_device_ops tap_netdev_ops = {
         .ndo_stop               = tun_net_close,
         .ndo_start_xmit         = tun_net_xmit,
         .ndo_change_mtu         = tun_net_change_mtu,
+        .ndo_fix_features       = tun_net_fix_features,
         .ndo_set_multicast_list = tun_net_mclist,
         .ndo_set_mac_address    = eth_mac_addr,
         .ndo_validate_addr      = eth_validate_addr,
@@ -628,8 +640,7 @@ static __inline__ ssize_t tun_get_user(struct tun_struct *tun,
                         kfree_skb(skb);
                         return -EINVAL;
                 }
-        } else if (tun->flags & TUN_NOCHECKSUM)
-                skb->ip_summed = CHECKSUM_UNNECESSARY;
+        }
 
         switch (tun->flags & TUN_TYPE_MASK) {
         case TUN_TUN_DEV:
@@ -1094,6 +1105,10 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
                                 goto err_free_sk;
                 }
 
+                dev->hw_features = NETIF_F_SG | NETIF_F_FRAGLIST |
+                        TUN_USER_FEATURES;
+                dev->features = dev->hw_features;
+
                 err = register_netdevice(tun->dev);
                 if (err < 0)
                         goto err_free_sk;
@@ -1158,18 +1173,12 @@ static int tun_get_iff(struct net *net, struct tun_struct *tun,
 
 /* This is like a cut-down ethtool ops, except done via tun fd so no
  * privs required. */
-static int set_offload(struct net_device *dev, unsigned long arg)
+static int set_offload(struct tun_struct *tun, unsigned long arg)
 {
-        u32 old_features, features;
-
-        old_features = dev->features;
-        /* Unset features, set them as we chew on the arg. */
-        features = (old_features & ~(NETIF_F_HW_CSUM|NETIF_F_SG|NETIF_F_FRAGLIST
-                                    |NETIF_F_TSO_ECN|NETIF_F_TSO|NETIF_F_TSO6
-                                    |NETIF_F_UFO));
+        u32 features = 0;
 
         if (arg & TUN_F_CSUM) {
-                features |= NETIF_F_HW_CSUM|NETIF_F_SG|NETIF_F_FRAGLIST;
+                features |= NETIF_F_HW_CSUM;
                 arg &= ~TUN_F_CSUM;
 
                 if (arg & (TUN_F_TSO4|TUN_F_TSO6)) {
@@ -1195,9 +1204,8 @@ static int set_offload(struct net_device *dev, unsigned long arg)
         if (arg)
                 return -EINVAL;
 
-        dev->features = features;
-        if (old_features != dev->features)
-                netdev_features_change(dev);
+        tun->set_features = features;
+        netdev_update_features(tun->dev);
 
         return 0;
 }
@@ -1262,12 +1270,9 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 
         case TUNSETNOCSUM:
                 /* Disable/Enable checksum */
-                if (arg)
-                        tun->flags |= TUN_NOCHECKSUM;
-                else
-                        tun->flags &= ~TUN_NOCHECKSUM;
 
-                tun_debug(KERN_INFO, tun, "checksum %s\n",
+                /* [unimplemented] */
+                tun_debug(KERN_INFO, tun, "ignored: set checksum %s\n",
                           arg ? "disabled" : "enabled");
                 break;
 
@@ -1316,7 +1321,7 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
                 break;
 #endif
         case TUNSETOFFLOAD:
-                ret = set_offload(tun->dev, arg);
+                ret = set_offload(tun, arg);
                 break;
 
         case TUNSETTXFILTER:
@@ -1595,30 +1600,12 @@ static void tun_set_msglevel(struct net_device *dev, u32 value)
 #endif
 }
 
-static u32 tun_get_rx_csum(struct net_device *dev)
-{
-        struct tun_struct *tun = netdev_priv(dev);
-        return (tun->flags & TUN_NOCHECKSUM) == 0;
-}
-
-static int tun_set_rx_csum(struct net_device *dev, u32 data)
-{
-        struct tun_struct *tun = netdev_priv(dev);
-        if (data)
-                tun->flags &= ~TUN_NOCHECKSUM;
-        else
-                tun->flags |= TUN_NOCHECKSUM;
-        return 0;
-}
-
 static const struct ethtool_ops tun_ethtool_ops = {
         .get_settings   = tun_get_settings,
         .get_drvinfo    = tun_get_drvinfo,
         .get_msglevel   = tun_get_msglevel,
         .set_msglevel   = tun_set_msglevel,
         .get_link       = ethtool_op_get_link,
-        .get_rx_csum    = tun_get_rx_csum,
-        .set_rx_csum    = tun_set_rx_csum
 };