tun: Fix TUN_PKT_STRIP setting

We set the flag TUN_PKT_STRIP if the user buffer provided is too
small to contain the entire packet plus meta-data.  However, this
has been broken ever since we added GSO meta-data.  VLAN acceleration
also has the same problem.

This patch fixes this by taking both into account when setting the
TUN_PKT_STRIP flag.

The fact that this has been broken for six years without anyone
realising means that nobody actually uses this flag.

Fixes: f43798c27684 ("tun: Allow GSO using virtio_net_hdr")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 4 deletions

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 57e6bf75a632..9dd3746994a4 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1236,15 +1236,19 @@ static ssize_t tun_put_user(struct tun_struct *tun,
         ssize_t total = 0;
         int vlan_offset = 0, copied;
         int vlan_hlen = 0;
+        int vnet_hdr_sz = 0;
 
         if (vlan_tx_tag_present(skb))
                 vlan_hlen = VLAN_HLEN;
 
+        if (tun->flags & TUN_VNET_HDR)
+                vnet_hdr_sz = tun->vnet_hdr_sz;
+
         if (!(tun->flags & TUN_NO_PI)) {
                 if ((len -= sizeof(pi)) < 0)
                         return -EINVAL;
 
-                if (len < skb->len) {
+                if (len < skb->len + vlan_hlen + vnet_hdr_sz) {
                         /* Packet will be striped */
                         pi.flags |= TUN_PKT_STRIP;
                 }
@@ -1254,9 +1258,9 @@ static ssize_t tun_put_user(struct tun_struct *tun,
                 total += sizeof(pi);
         }
 
-        if (tun->flags & TUN_VNET_HDR) {
+        if (vnet_hdr_sz) {
                 struct virtio_net_hdr gso = { 0 }; /* no info leak */
-                if ((len -= tun->vnet_hdr_sz) < 0)
+                if ((len -= vnet_hdr_sz) < 0)
                         return -EINVAL;
 
                 if (skb_is_gso(skb)) {
@@ -1298,7 +1302,7 @@ static ssize_t tun_put_user(struct tun_struct *tun,
                 if (unlikely(memcpy_toiovecend(iv, (void *)&gso, total,
                                                sizeof(gso))))
                         return -EFAULT;
-                total += tun->vnet_hdr_sz;
+                total += vnet_hdr_sz;
         }
 
         copied = total;