netfilter: nft_payload: work around vlan header stripping

make payload expression aware of the fact that VLAN offload may have
removed a vlan header.

When we encounter tagged skb, transparently insert the tag into the
register so that vlan header matching can work without userspace being
aware of offload features.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/netfilter/nft_payload.c b/net/netfilter/nft_payload.c
index 94fb3b2..09b4b07 100644 (file)
--- a/net/netfilter/nft_payload.c
+++ b/net/netfilter/nft_payload.c
@@ -9,6 +9,7 @@
  */
 
 #include <linux/kernel.h>
+#include <linux/if_vlan.h>
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/netlink.h>
@@ -17,6 +18,53 @@
 #include <net/netfilter/nf_tables_core.h>
 #include <net/netfilter/nf_tables.h>
 
+/* add vlan header into the user buffer for if tag was removed by offloads */
+static bool
+nft_payload_copy_vlan(u32 *d, const struct sk_buff *skb, u8 offset, u8 len)
+{
+       int mac_off = skb_mac_header(skb) - skb->data;
+       u8 vlan_len, *vlanh, *dst_u8 = (u8 *) d;
+       struct vlan_ethhdr veth;
+
+       vlanh = (u8 *) &veth;
+       if (offset < ETH_HLEN) {
+               u8 ethlen = min_t(u8, len, ETH_HLEN - offset);
+
+               if (skb_copy_bits(skb, mac_off, &veth, ETH_HLEN))
+                       return false;
+
+               veth.h_vlan_proto = skb->vlan_proto;
+
+               memcpy(dst_u8, vlanh + offset, ethlen);
+
+               len -= ethlen;
+               if (len == 0)
+                       return true;
+
+               dst_u8 += ethlen;
+               offset = ETH_HLEN;
+       } else if (offset >= VLAN_ETH_HLEN) {
+               offset -= VLAN_HLEN;
+               goto skip;
+       }
+
+       veth.h_vlan_TCI = htons(skb_vlan_tag_get(skb));
+       veth.h_vlan_encapsulated_proto = skb->protocol;
+
+       vlanh += offset;
+
+       vlan_len = min_t(u8, len, VLAN_ETH_HLEN - offset);
+       memcpy(dst_u8, vlanh, vlan_len);
+
+       len -= vlan_len;
+       if (!len)
+               return true;
+
+       dst_u8 += vlan_len;
+ skip:
+       return skb_copy_bits(skb, offset + mac_off, dst_u8, len) == 0;
+}
+
 static void nft_payload_eval(const struct nft_expr *expr,
                             struct nft_regs *regs,
                             const struct nft_pktinfo *pkt)
@@ -26,10 +74,18 @@ static void nft_payload_eval(const struct nft_expr *expr,
        u32 *dest = &regs->data[priv->dreg];
        int offset;
 
+       dest[priv->len / NFT_REG32_SIZE] = 0;
        switch (priv->base) {
        case NFT_PAYLOAD_LL_HEADER:
                if (!skb_mac_header_was_set(skb))
                        goto err;
+
+               if (skb_vlan_tag_present(skb)) {
+                       if (!nft_payload_copy_vlan(dest, skb,
+                                                  priv->offset, priv->len))
+                               goto err;
+                       return;
+               }
                offset = skb_mac_header(skb) - skb->data;
                break;
        case NFT_PAYLOAD_NETWORK_HEADER:
@@ -43,7 +99,6 @@ static void nft_payload_eval(const struct nft_expr *expr,
        }
        offset += priv->offset;
 
-       dest[priv->len / NFT_REG32_SIZE] = 0;
        if (skb_copy_bits(skb, offset, dest, priv->len) < 0)
                goto err;
        return;