net: filter: add vlan tag access

BPF filters lack ability to access skb->vlan_tci

This patch adds two new ancillary accessors :

SKF_AD_VLAN_TAG         (44) mapped to vlan_tx_tag_get(skb)

SKF_AD_VLAN_TAG_PRESENT (48) mapped to vlan_tx_tag_present(skb)

This allows libpcap/tcpdump to use a kernel filter instead of
having to fallback to accept all packets, then filter them in
user space.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Suggested-by: Ani Sinha <ani@aristanetworks.com>
Suggested-by: Daniel Borkmann <danborkmann@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 0 deletions

diff --git a/net/core/filter.c b/net/core/filter.c
index 3d92ebb7fbcf..5a114d41bf11 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -39,6 +39,7 @@
 #include <linux/reciprocal_div.h>
 #include <linux/ratelimit.h>
 #include <linux/seccomp.h>
+#include <linux/if_vlan.h>
 
 /* No hurry in this branch
  *
@@ -341,6 +342,12 @@ load_b:
                 case BPF_S_ANC_CPU:
                         A = raw_smp_processor_id();
                         continue;
+                case BPF_S_ANC_VLAN_TAG:
+                        A = vlan_tx_tag_get(skb);
+                        continue;
+                case BPF_S_ANC_VLAN_TAG_PRESENT:
+                        A = !!vlan_tx_tag_present(skb);
+                        continue;
                 case BPF_S_ANC_NLATTR: {
                         struct nlattr *nla;
 
@@ -600,6 +607,8 @@ int sk_chk_filter(struct sock_filter *filter, unsigned int flen)
                         ANCILLARY(RXHASH);
                         ANCILLARY(CPU);
                         ANCILLARY(ALU_XOR_X);
+                        ANCILLARY(VLAN_TAG);
+                        ANCILLARY(VLAN_TAG_PRESENT);
                         }
                 }
                 ftest->code = code;