net: skbuff: Limit skb_vlan_pop/push() to expect skb->data at mac header

skb_vlan_pop/push were too generic, trying to support the cases where
skb->data is at mac header, and cases where skb->data is arbitrarily
elsewhere.

Supporting an arbitrary skb->data was complex and bogus:
 - It failed to unwind skb->data to its original location post actual
   pop/push.
   (Also, semantic is not well defined for unwinding: If data was into
    the eth header, need to use same offset from start; But if data was
    at network header or beyond, need to adjust the original offset
    according to the push/pull)
 - It mangled the rcsum post actual push/pop, without taking into account
   that the eth bytes might already have been pulled out of the csum.

Most callers (ovs, bpf) already had their skb->data at mac_header upon
invoking skb_vlan_pop/push.
Last caller that failed to do so (act_vlan) has been recently fixed.

Therefore, to simplify things, no longer support arbitrary skb->data
inputs for skb_vlan_pop/push().

skb->data is expected to be exactly at mac_header; WARN otherwise.

Signed-off-by: Shmulik Ladkani <shmulik.ladkani@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Pravin Shelar <pshelar@ovn.org>
Cc: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index d36c754..cbd19d2 100644 (file)
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -4528,13 +4528,18 @@ EXPORT_SYMBOL(skb_ensure_writable);
 int __skb_vlan_pop(struct sk_buff *skb, u16 *vlan_tci)
 {
        struct vlan_hdr *vhdr;
-       unsigned int offset = skb->data - skb_mac_header(skb);
+       int offset = skb->data - skb_mac_header(skb);
        int err;
 
-       __skb_push(skb, offset);
+       if (WARN_ONCE(offset,
+                     "__skb_vlan_pop got skb with skb->data not at mac header (offset %d)\n",
+                     offset)) {
+               return -EINVAL;
+       }
+
        err = skb_ensure_writable(skb, VLAN_ETH_HLEN);
        if (unlikely(err))
-               goto pull;
+               return err;
 
        skb_postpull_rcsum(skb, skb->data + (2 * ETH_ALEN), VLAN_HLEN);
 
@@ -4551,13 +4556,14 @@ int __skb_vlan_pop(struct sk_buff *skb, u16 *vlan_tci)
                skb_set_network_header(skb, ETH_HLEN);
 
        skb_reset_mac_len(skb);
-pull:
-       __skb_pull(skb, offset);
 
        return err;
 }
 EXPORT_SYMBOL(__skb_vlan_pop);
 
+/* Pop a vlan tag either from hwaccel or from payload.
+ * Expects skb->data at mac header.
+ */
 int skb_vlan_pop(struct sk_buff *skb)
 {
        u16 vlan_tci;
@@ -4588,29 +4594,30 @@ int skb_vlan_pop(struct sk_buff *skb)
 }
 EXPORT_SYMBOL(skb_vlan_pop);
 
+/* Push a vlan tag either into hwaccel or into payload (if hwaccel tag present).
+ * Expects skb->data at mac header.
+ */
 int skb_vlan_push(struct sk_buff *skb, __be16 vlan_proto, u16 vlan_tci)
 {
        if (skb_vlan_tag_present(skb)) {
-               unsigned int offset = skb->data - skb_mac_header(skb);
+               int offset = skb->data - skb_mac_header(skb);
                int err;
 
-               /* __vlan_insert_tag expect skb->data pointing to mac header.
-                * So change skb->data before calling it and change back to
-                * original position later
-                */
-               __skb_push(skb, offset);
+               if (WARN_ONCE(offset,
+                             "skb_vlan_push got skb with skb->data not at mac header (offset %d)\n",
+                             offset)) {
+                       return -EINVAL;
+               }
+
                err = __vlan_insert_tag(skb, skb->vlan_proto,
                                        skb_vlan_tag_get(skb));
-               if (err) {
-                       __skb_pull(skb, offset);
+               if (err)
                        return err;
-               }
 
                skb->protocol = skb->vlan_proto;
                skb->mac_len += VLAN_HLEN;
 
                skb_postpush_rcsum(skb, skb->data + (2 * ETH_ALEN), VLAN_HLEN);
-               __skb_pull(skb, offset);
        }
        __vlan_hwaccel_put_tag(skb, vlan_proto, vlan_tci);
        return 0;