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>

7 files changed, 35 insertions, 3 deletions

diff --git a/Documentation/networking/filter.txt b/Documentation/networking/filter.txt
index 9930ecfbb465..135581f015e1 100644
--- a/Documentation/networking/filter.txt
+++ b/Documentation/networking/filter.txt
@@ -280,7 +280,8 @@ Possible BPF extensions are shown in the following table:
   rxhash                                skb->hash
   cpu                                   raw_smp_processor_id()
   vlan_tci                              skb_vlan_tag_get(skb)
-  vlan_pr                               skb_vlan_tag_present(skb)
+  vlan_avail                            skb_vlan_tag_present(skb)
+  vlan_tpid                             skb->vlan_proto
   rand                                  prandom_u32()
 
 These extensions can also be prefixed with '#'.
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 9ee8c67ea249..fa11b3a367be 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -454,6 +454,7 @@ static inline u16 bpf_anc_helper(const struct sock_filter *ftest)
                 BPF_ANCILLARY(VLAN_TAG_PRESENT);
                 BPF_ANCILLARY(PAY_OFFSET);
                 BPF_ANCILLARY(RANDOM);
+                BPF_ANCILLARY(VLAN_TPID);
                 }
                 /* Fallthrough. */
         default:
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 3dd314a45d0d..27dc4ec58840 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -182,6 +182,7 @@ struct __sk_buff {
         __u32 protocol;
         __u32 vlan_present;
         __u32 vlan_tci;
+        __u32 vlan_proto;
 };
 
 #endif /* _UAPI__LINUX_BPF_H__ */
diff --git a/include/uapi/linux/filter.h b/include/uapi/linux/filter.h
index 47785d5ecf17..34c7936ca114 100644
--- a/include/uapi/linux/filter.h
+++ b/include/uapi/linux/filter.h
@@ -77,7 +77,8 @@ struct sock_fprog {	/* Required for SO_ATTACH_FILTER. */
 #define SKF_AD_VLAN_TAG_PRESENT 48
 #define SKF_AD_PAY_OFFSET       52
 #define SKF_AD_RANDOM   56
-#define SKF_AD_MAX      60
+#define SKF_AD_VLAN_TPID        60
+#define SKF_AD_MAX      64
 #define SKF_NET_OFF   (-0x100000)
 #define SKF_LL_OFF    (-0x200000)
 
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);
 
diff --git a/tools/net/bpf_exp.l b/tools/net/bpf_exp.l
index 833a96611da6..c83af3fb77de 100644
--- a/tools/net/bpf_exp.l
+++ b/tools/net/bpf_exp.l
@@ -92,6 +92,8 @@ extern void yyerror(const char *str);
 "#"?("cpu")     { return K_CPU; }
 "#"?("vlan_tci") { return K_VLANT; }
 "#"?("vlan_pr") { return K_VLANP; }
+"#"?("vlan_avail")      { return K_VLANP; }
+"#"?("vlan_tpid")       { return K_VLANTPID; }
 "#"?("rand")    { return K_RAND; }
 
 ":"             { return ':'; }
diff --git a/tools/net/bpf_exp.y b/tools/net/bpf_exp.y
index e6306c51c26f..f8332749b44c 100644
--- a/tools/net/bpf_exp.y
+++ b/tools/net/bpf_exp.y
@@ -56,7 +56,7 @@ static void bpf_set_jmp_label(char *label, enum jmp_type type);
 %token OP_LDXI
 
 %token K_PKT_LEN K_PROTO K_TYPE K_NLATTR K_NLATTR_NEST K_MARK K_QUEUE K_HATYPE
-%token K_RXHASH K_CPU K_IFIDX K_VLANT K_VLANP K_POFF K_RAND
+%token K_RXHASH K_CPU K_IFIDX K_VLANT K_VLANP K_VLANTPID K_POFF K_RAND
 
 %token ':' ',' '[' ']' '(' ')' 'x' 'a' '+' 'M' '*' '&' '#' '%'
 
@@ -167,6 +167,9 @@ ldb
         | OP_LDB K_RAND {
                 bpf_set_curr_instr(BPF_LD | BPF_B | BPF_ABS, 0, 0,
                                    SKF_AD_OFF + SKF_AD_RANDOM); }
+        | OP_LDB K_VLANTPID {
+                bpf_set_curr_instr(BPF_LD | BPF_B | BPF_ABS, 0, 0,
+                                   SKF_AD_OFF + SKF_AD_VLAN_TPID); }
         ;
 
 ldh
@@ -218,6 +221,9 @@ ldh
         | OP_LDH K_RAND {
                 bpf_set_curr_instr(BPF_LD | BPF_H | BPF_ABS, 0, 0,
                                    SKF_AD_OFF + SKF_AD_RANDOM); }
+        | OP_LDH K_VLANTPID {
+                bpf_set_curr_instr(BPF_LD | BPF_H | BPF_ABS, 0, 0,
+                                   SKF_AD_OFF + SKF_AD_VLAN_TPID); }
         ;
 
 ldi
@@ -274,6 +280,9 @@ ld
         | OP_LD K_RAND {
                 bpf_set_curr_instr(BPF_LD | BPF_W | BPF_ABS, 0, 0,
                                    SKF_AD_OFF + SKF_AD_RANDOM); }
+        | OP_LD K_VLANTPID {
+                bpf_set_curr_instr(BPF_LD | BPF_W | BPF_ABS, 0, 0,
+                                   SKF_AD_OFF + SKF_AD_VLAN_TPID); }
         | OP_LD 'M' '[' number ']' {
                 bpf_set_curr_instr(BPF_LD | BPF_MEM, 0, 0, $4); }
         | OP_LD '[' 'x' '+' number ']' {