net/mlx5e: Use struct_group() for memcpy() region

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memcpy(), memmove(), and memset(), avoid
intentionally writing across neighboring fields.

Use struct_group() in struct vlan_ethhdr around members h_dest and
h_source, so they can be referenced together. This will allow memcpy()
and sizeof() to more easily reason about sizes, improve readability,
and avoid future warnings about writing beyond the end of h_dest.

"pahole" shows no size nor member offset changes to struct vlan_ethhdr.
"objdump -d" shows no object code changes.

Fixes: 34802a42b352 ("net/mlx5e: Do not modify the TX SKB")
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c
index 7fd33b3..ee7ecb8 100644 (file)
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c
@@ -208,7 +208,7 @@ static inline void mlx5e_insert_vlan(void *start, struct sk_buff *skb, u16 ihs)
        int cpy1_sz = 2 * ETH_ALEN;
        int cpy2_sz = ihs - cpy1_sz;
 
-       memcpy(vhdr, skb->data, cpy1_sz);
+       memcpy(&vhdr->addrs, skb->data, cpy1_sz);
        vhdr->h_vlan_proto = skb->vlan_proto;
        vhdr->h_vlan_TCI = cpu_to_be16(skb_vlan_tag_get(skb));
        memcpy(&vhdr->h_vlan_encapsulated_proto, skb->data + cpy1_sz, cpy2_sz);

diff --git a/include/linux/if_vlan.h b/include/linux/if_vlan.h
index 8420fe5..2be4dd7 100644 (file)
--- a/include/linux/if_vlan.h
+++ b/include/linux/if_vlan.h
@@ -46,8 +46,10 @@ struct vlan_hdr {
  *     @h_vlan_encapsulated_proto: packet type ID or len
  */
 struct vlan_ethhdr {
-       unsigned char   h_dest[ETH_ALEN];
-       unsigned char   h_source[ETH_ALEN];
+       struct_group(addrs,
+               unsigned char   h_dest[ETH_ALEN];
+               unsigned char   h_source[ETH_ALEN];
+       );
        __be16          h_vlan_proto;
        __be16          h_vlan_TCI;
        __be16          h_vlan_encapsulated_proto;