filter: introduce SKF_AD_VLAN_TPID BPF extension

If vlan offloading takes place then vlan header is removed from frame
and its contents, both vlan_tci and vlan_proto, is available to user
space via TPACKET interface. However, only vlan_tci can be used in BPF
filters.

This commit introduces a new BPF extension. It makes possible to load
the value of vlan_proto (vlan TPID) to register A. Support for classic
BPF and eBPF is being added, analogous to skb->protocol.

Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Jiri Pirko <jpirko@redhat.com>

Signed-off-by: Michal Sekletar <msekleta@redhat.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Reviewed-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 17 insertions, 0 deletions

diff --git a/net/core/filter.c b/net/core/filter.c
index 084eacc4d1d4..32f43c59908c 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -272,6 +272,16 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
                 insn += cnt - 1;
                 break;
 
+        case SKF_AD_OFF + SKF_AD_VLAN_TPID:
+                BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, vlan_proto) != 2);
+
+                /* A = *(u16 *) (CTX + offsetof(vlan_proto)) */
+                *insn++ = BPF_LDX_MEM(BPF_H, BPF_REG_A, BPF_REG_CTX,
+                                      offsetof(struct sk_buff, vlan_proto));
+                /* A = ntohs(A) [emitting a nop or swap16] */
+                *insn = BPF_ENDIAN(BPF_FROM_BE, BPF_REG_A, 16);
+                break;
+
         case SKF_AD_OFF + SKF_AD_PAY_OFFSET:
         case SKF_AD_OFF + SKF_AD_NLATTR:
         case SKF_AD_OFF + SKF_AD_NLATTR_NEST:
@@ -1226,6 +1236,13 @@ static u32 sk_filter_convert_ctx_access(int dst_reg, int src_reg, int ctx_off,
                                       offsetof(struct sk_buff, protocol));
                 break;
 
+        case offsetof(struct __sk_buff, vlan_proto):
+                BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, vlan_proto) != 2);
+
+                *insn++ = BPF_LDX_MEM(BPF_H, dst_reg, src_reg,
+                                      offsetof(struct sk_buff, vlan_proto));
+                break;
+
         case offsetof(struct __sk_buff, mark):
                 return convert_skb_access(SKF_AD_MARK, dst_reg, src_reg, insn);