Re: bpf filter : support for vlan tag

On Mon, 2012-10-15 at 19:10 -0700, Ani Sinha wrote:

Hi :

I was looking at the kernel side implementation of the BPF filter. I
do not see any code that supports filtering of packets based on
provided vlan tag information from the skbuff. This will make it
impossible to provide any filter to tcpdump that will filter packets
based on the tag information if libpcap uses the kernel filter.

Any help will be much appreciated.

Right, we need a basic support, using a new ancillary definition.

Is the following patch enough to address your need, or do you also need
access to vlan_tx_tag_present() ?

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 24d251f..0218e41 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h

@@ -123,6 +123,7 @@ enum {
 	BPF_S_ANC_CPU,
 	BPF_S_ANC_ALU_XOR_X,
 	BPF_S_ANC_SECCOMP_LD_W,
+	BPF_S_ANC_VLAN_TAG,
 };
 
 #endif /* __LINUX_FILTER_H__ */

diff --git a/net/core/filter.c b/net/core/filter.c
index 3d92ebb..de4a5dc 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c

@@ -341,6 +341,9 @@ 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_NLATTR: {
 			struct nlattr *nla;
 

@@ -600,6 +603,7 @@ int sk_chk_filter(struct sock_filter *filter, unsigned int flen)
 			ANCILLARY(RXHASH);
 			ANCILLARY(CPU);
 			ANCILLARY(ALU_XOR_X);
+			ANCILLARY(VLAN_TAG);
 			}
 		}
 		ftest->code = code;