Re: bpf filter : support for vlan tag

[Eric Dumazet <eric.dumazet@gmail.com>]

On Tue, 2012-10-16 at 13:00 +0200, Daniel Borkmann wrote:
> On Tue, Oct 16, 2012 at 8:46 AM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> > 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() ?
> 
> I like this patch, it's especially useful to speed up processing for
> packet analyzers. vlan_tx_tag_present() might also be good to have if
> this doesn't waste to much room for future ancillary operations.

There is plenty of room in ancillary space

Note that if speed is needed, we also want to update various JIT
implementations.

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 24d251f..c9f0005 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -123,6 +123,8 @@ enum {
 	BPF_S_ANC_CPU,
 	BPF_S_ANC_ALU_XOR_X,
 	BPF_S_ANC_SECCOMP_LD_W,
+	BPF_S_ANC_VLAN_TAG,
+	BPF_S_ANC_VLAN_TAG_PRESENT,
 };
 
 #endif /* __LINUX_FILTER_H__ */
diff --git a/include/uapi/linux/filter.h b/include/uapi/linux/filter.h
index 3d79224..9cfde69 100644
--- a/include/uapi/linux/filter.h
+++ b/include/uapi/linux/filter.h
@@ -127,7 +127,9 @@ struct sock_fprog {	/* Required for SO_ATTACH_FILTER. */
 #define SKF_AD_RXHASH	32
 #define SKF_AD_CPU	36
 #define SKF_AD_ALU_XOR_X	40
-#define SKF_AD_MAX	44
+#define SKF_AD_VLAN_TAG	44
+#define SKF_AD_VLAN_TAG_PRESENT 48
+#define SKF_AD_MAX	52
 #define SKF_NET_OFF   (-0x100000)
 #define SKF_LL_OFF    (-0x200000)
 
diff --git a/net/core/filter.c b/net/core/filter.c
index 3d92ebb..5a114d4 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;