[PATCH net-next 1/2] bpf: make programs see skb->data == L2 for ingress and egress

[PATCH net-next 1/2] bpf: make programs see skb->data == L2 for ingress and egress

[Alexei Starovoitov]

eBPF programs attached to ingress and egress qdiscs see inconsistent skb->data.
For ingress L2 header is already pulled, whereas for egress it's present.
This is known to program writers which are currently forced to use
BPF_LL_OFF workaround.
Since programs don't change skb internal pointers it is safe to do
pull/push right around invocation of the program and earlier taps and
later pt->func() will not be affected.
Multiple taps via packet_rcv(), tpacket_rcv() are doing the same trick
around run_filter/BPF_PROG_RUN even if skb_shared.

This fix finally allows programs to use optimized LD_ABS/IND instructions
without BPF_LL_OFF for higher performance.
tc ingress + cls_bpf + samples/bpf/tcbpf1_kern.o
       w/o JIT   w/JIT
before  20.5     23.6 Mpps
after   21.8     26.6 Mpps

Old programs with BPF_LL_OFF will still work as-is.

We can now undo most of the earlier workaround commit:
a166151cbe33 ("bpf: fix bpf helpers to use skb->mac_header relative offsets")

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
---

Earlier versions were trying to do too much to make ingress and egress qdisc
consistent for all classifiers and actions or had too big of a scope of push/pull:
v1: http://thread.gmane.org/gmane.linux.network/358168/focus=358168
v2: http://thread.gmane.org/gmane.linux.network/358524/focus=358532
v3: http://thread.gmane.org/gmane.linux.network/358733/focus=358734
v4: http://thread.gmane.org/gmane.linux.network/359129/focus=359694

skb->data will still be different for all non-bpf classifiers/actions.

This fix will still allow us to explore further optimizations like
moving skb_pull() from eth_type_trans() into netif_receive_skb() in the future.

Here is how ingress callchain looks:

netif_receive_skb,          // likely skb->users == 1
  deliver_skb
    packet_rcv              // skb->users == 2
      orig_skb_data = skb->data
      push l2
      res = BPF_PROG_RUN
      if (!res) {
        skb->data = orig_skb_data
        consume_skb(skb)    // skb->users == 1
        goto out
      }

      skb2 = skb_clone(skb)
      skb->data = orig_skb_data
      consume_skb(skb)      // skb->users == 1
      __skb_queue_tail(skb2)

  deliver_skb
    Tpacket_rcv             // skb->users == 2
      orig_skb_data = skb->data
      push l2
      res = BPF_PROG_RUN
      if (!res) {
        skb->data = orig_skb_data
        kfree_skb(skb)      // skb->users == 1
	goto out
      }

      if (...) {
        skb2 = skb_clone(skb)
        __skb_queue_tail(skb2)
      }
      skb_copy_bits(skb)
      skb->data = orig_skb_data
      kfree_skb(skb)        // skb->users == 1

  tc_classify
     cls_u32 and other classifiers don't touch skb
       actions like mirred do clone before redirect, etc.

     cls_bpf               // skb->users == 1
       push l2
       res = BPF_PROG_RUN
       pull l2
       actions             // still see skb->data at L3

     cls_xxx               // still see skb->data at L3
       actions

  netfilter
  vlan_do_receive
  bridge

  deliver_skb
    mpls_forward and other ptype specific taps

  ip_rcv                   // skb->users == 1

 net/core/filter.c         |   27 +++------------------------
 net/sched/act_bpf.c       |    9 ++++++++-
 net/sched/cls_bpf.c       |   12 +++++++++++-
 samples/bpf/tcbpf1_kern.c |    8 ++++----
 4 files changed, 26 insertions(+), 30 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 64c121c09655..e76b8ec1b0ac 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -1239,21 +1239,6 @@ int sk_attach_bpf(u32 ufd, struct sock *sk)
 	return 0;
 }
 
-/**
- *	bpf_skb_clone_not_writable - is the header of a clone not writable
- *	@skb: buffer to check
- *	@len: length up to which to write, can be negative
- *
- *	Returns true if modifying the header part of the cloned buffer
- *	does require the data to be copied. I.e. this version works with
- *	negative lengths needed for eBPF case!
- */
-static bool bpf_skb_clone_unwritable(const struct sk_buff *skb, int len)
-{
-	return skb_header_cloned(skb) ||
-	       (int) skb_headroom(skb) + len > skb->hdr_len;
-}
-
 #define BPF_RECOMPUTE_CSUM(flags)	((flags) & 1)
 
 static u64 bpf_skb_store_bytes(u64 r1, u64 r2, u64 r3, u64 r4, u64 flags)
@@ -1276,9 +1261,8 @@ static u64 bpf_skb_store_bytes(u64 r1, u64 r2, u64 r3, u64 r4, u64 flags)
 	if (unlikely((u32) offset > 0xffff || len > sizeof(buf)))
 		return -EFAULT;
 
-	offset -= skb->data - skb_mac_header(skb);
 	if (unlikely(skb_cloned(skb) &&
-		     bpf_skb_clone_unwritable(skb, offset + len)))
+		     !skb_clone_writable(skb, offset + len)))
 		return -EFAULT;
 
 	ptr = skb_header_pointer(skb, offset, len, buf);
@@ -1322,9 +1306,8 @@ static u64 bpf_l3_csum_replace(u64 r1, u64 r2, u64 from, u64 to, u64 flags)
 	if (unlikely((u32) offset > 0xffff))
 		return -EFAULT;
 
-	offset -= skb->data - skb_mac_header(skb);
 	if (unlikely(skb_cloned(skb) &&
-		     bpf_skb_clone_unwritable(skb, offset + sizeof(sum))))
+		     !skb_clone_writable(skb, offset + sizeof(sum))))
 		return -EFAULT;
 
 	ptr = skb_header_pointer(skb, offset, sizeof(sum), &sum);
@@ -1370,9 +1353,8 @@ static u64 bpf_l4_csum_replace(u64 r1, u64 r2, u64 from, u64 to, u64 flags)
 	if (unlikely((u32) offset > 0xffff))
 		return -EFAULT;
 
-	offset -= skb->data - skb_mac_header(skb);
 	if (unlikely(skb_cloned(skb) &&
-		     bpf_skb_clone_unwritable(skb, offset + sizeof(sum))))
+		     !skb_clone_writable(skb, offset + sizeof(sum))))
 		return -EFAULT;
 
 	ptr = skb_header_pointer(skb, offset, sizeof(sum), &sum);
@@ -1426,9 +1408,6 @@ static u64 bpf_clone_redirect(u64 r1, u64 ifindex, u64 flags, u64 r4, u64 r5)
 	if (unlikely(!skb2))
 		return -ENOMEM;
 
-	if (G_TC_AT(skb2->tc_verd) & AT_INGRESS)
-		skb_push(skb2, skb2->mac_len);
-
 	if (BPF_IS_REDIRECT_INGRESS(flags))
 		return dev_forward_skb(dev, skb2);
 
diff --git a/net/sched/act_bpf.c b/net/sched/act_bpf.c
index dc6a2d324bd8..b32367deab77 100644
--- a/net/sched/act_bpf.c
+++ b/net/sched/act_bpf.c
@@ -37,6 +37,7 @@ static int tcf_bpf(struct sk_buff *skb, const struct tc_action *act,
 {
 	struct tcf_bpf *prog = act->priv;
 	int action, filter_res;
+	u32 at_ingress = G_TC_AT(skb->tc_verd) & AT_INGRESS;
 
 	if (unlikely(!skb_mac_header_was_set(skb)))
 		return TC_ACT_UNSPEC;
@@ -48,7 +49,13 @@ static int tcf_bpf(struct sk_buff *skb, const struct tc_action *act,
 
 	/* Needed here for accessing maps. */
 	rcu_read_lock();
-	filter_res = BPF_PROG_RUN(prog->filter, skb);
+	if (at_ingress) {
+		__skb_push(skb, skb->mac_len);
+		filter_res = BPF_PROG_RUN(prog->filter, skb);
+		__skb_pull(skb, skb->mac_len);
+	} else {
+		filter_res = BPF_PROG_RUN(prog->filter, skb);
+	}
 	rcu_read_unlock();
 
 	/* A BPF program may overwrite the default action opcode.
diff --git a/net/sched/cls_bpf.c b/net/sched/cls_bpf.c
index 91bd9c19471d..0e5e747c73f3 100644
--- a/net/sched/cls_bpf.c
+++ b/net/sched/cls_bpf.c
@@ -64,6 +64,7 @@ static int cls_bpf_classify(struct sk_buff *skb, const struct tcf_proto *tp,
 {
 	struct cls_bpf_head *head = rcu_dereference_bh(tp->root);
 	struct cls_bpf_prog *prog;
+	u32 at_ingress = G_TC_AT(skb->tc_verd) & AT_INGRESS;
 	int ret = -1;
 
 	if (unlikely(!skb_mac_header_was_set(skb)))
@@ -72,7 +73,16 @@ static int cls_bpf_classify(struct sk_buff *skb, const struct tcf_proto *tp,
 	/* Needed here for accessing maps. */
 	rcu_read_lock();
 	list_for_each_entry_rcu(prog, &head->plist, link) {
-		int filter_res = BPF_PROG_RUN(prog->filter, skb);
+		int filter_res;
+
+		if (at_ingress) {
+			/* It is safe to push/pull even if skb_shared() */
+			__skb_push(skb, skb->mac_len);
+			filter_res = BPF_PROG_RUN(prog->filter, skb);
+			__skb_pull(skb, skb->mac_len);
+		} else {
+			filter_res = BPF_PROG_RUN(prog->filter, skb);
+		}
 
 		if (filter_res == 0)
 			continue;
diff --git a/samples/bpf/tcbpf1_kern.c b/samples/bpf/tcbpf1_kern.c
index 7c27710f8296..9bfb2eb34563 100644
--- a/samples/bpf/tcbpf1_kern.c
+++ b/samples/bpf/tcbpf1_kern.c
@@ -21,7 +21,7 @@ static inline void set_dst_mac(struct __sk_buff *skb, char *mac)
 
 static inline void set_ip_tos(struct __sk_buff *skb, __u8 new_tos)
 {
-	__u8 old_tos = load_byte(skb, BPF_LL_OFF + TOS_OFF);
+	__u8 old_tos = load_byte(skb, TOS_OFF);
 
 	bpf_l3_csum_replace(skb, IP_CSUM_OFF, htons(old_tos), htons(new_tos), 2);
 	bpf_skb_store_bytes(skb, TOS_OFF, &new_tos, sizeof(new_tos), 0);
@@ -34,7 +34,7 @@ static inline void set_ip_tos(struct __sk_buff *skb, __u8 new_tos)
 
 static inline void set_tcp_ip_src(struct __sk_buff *skb, __u32 new_ip)
 {
-	__u32 old_ip = _htonl(load_word(skb, BPF_LL_OFF + IP_SRC_OFF));
+	__u32 old_ip = _htonl(load_word(skb, IP_SRC_OFF));
 
 	bpf_l4_csum_replace(skb, TCP_CSUM_OFF, old_ip, new_ip, IS_PSEUDO | sizeof(new_ip));
 	bpf_l3_csum_replace(skb, IP_CSUM_OFF, old_ip, new_ip, sizeof(new_ip));
@@ -44,7 +44,7 @@ static inline void set_tcp_ip_src(struct __sk_buff *skb, __u32 new_ip)
 #define TCP_DPORT_OFF (ETH_HLEN + sizeof(struct iphdr) + offsetof(struct tcphdr, dest))
 static inline void set_tcp_dest_port(struct __sk_buff *skb, __u16 new_port)
 {
-	__u16 old_port = htons(load_half(skb, BPF_LL_OFF + TCP_DPORT_OFF));
+	__u16 old_port = htons(load_half(skb, TCP_DPORT_OFF));
 
 	bpf_l4_csum_replace(skb, TCP_CSUM_OFF, old_port, new_port, sizeof(new_port));
 	bpf_skb_store_bytes(skb, TCP_DPORT_OFF, &new_port, sizeof(new_port), 0);
@@ -53,7 +53,7 @@ static inline void set_tcp_dest_port(struct __sk_buff *skb, __u16 new_port)
 SEC("classifier")
 int bpf_prog1(struct __sk_buff *skb)
 {
-	__u8 proto = load_byte(skb, BPF_LL_OFF + ETH_HLEN + offsetof(struct iphdr, protocol));
+	__u8 proto = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol));
 	long *value;
 
 	if (proto == IPPROTO_TCP) {
-- 
1.7.9.5

[PATCH net-next 2/2] bpf: allow programs to write to certain skb fields

[Alexei Starovoitov]

allow programs read/write skb->mark, tc_index fields and
((struct qdisc_skb_cb *)cb)->data.

mark and tc_index are generically useful in TC.
cb[0]-cb[4] are primarily used to pass arguments from one
program to another called via bpf_tail_call() which can
be seen in sockex3_kern.c example.

All fields of 'struct __sk_buff' are readable to socket and tc_cls_act progs.
mark, tc_index are writeable from tc_cls_act only.
cb[0]-cb[4] are writeable by both sockets and tc_cls_act.

Add verifier tests and improve sample code.

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
---
This patch is independent from previous push/pull l2 patch, but
they both modify net/core/filter.c, so sent together.

 include/linux/bpf.h         |    3 +-
 include/uapi/linux/bpf.h    |    2 +
 kernel/bpf/verifier.c       |   37 ++++++++++++-----
 net/core/filter.c           |   93 +++++++++++++++++++++++++++++++++++++------
 samples/bpf/sockex3_kern.c  |   35 +++++-----------
 samples/bpf/test_verifier.c |   84 +++++++++++++++++++++++++++++++++++++-
 6 files changed, 206 insertions(+), 48 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index ca854e5bb2f7..2235aee8096a 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -105,7 +105,8 @@ struct bpf_verifier_ops {
 	 */
 	bool (*is_valid_access)(int off, int size, enum bpf_access_type type);
 
-	u32 (*convert_ctx_access)(int dst_reg, int src_reg, int ctx_off,
+	u32 (*convert_ctx_access)(enum bpf_access_type type, int dst_reg,
+				  int src_reg, int ctx_off,
 				  struct bpf_insn *insn);
 };
 
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 42aa19abab86..602f05b7a275 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -248,6 +248,8 @@ struct __sk_buff {
 	__u32 priority;
 	__u32 ingress_ifindex;
 	__u32 ifindex;
+	__u32 tc_index;
+	__u32 cb[5];
 };
 
 #endif /* _UAPI__LINUX_BPF_H__ */
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index cfd9a40b9a5a..039d866fd36a 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1692,6 +1692,8 @@ static int do_check(struct verifier_env *env)
 			}
 
 		} else if (class == BPF_STX) {
+			enum bpf_reg_type dst_reg_type;
+
 			if (BPF_MODE(insn->code) == BPF_XADD) {
 				err = check_xadd(env, insn);
 				if (err)
@@ -1700,11 +1702,6 @@ static int do_check(struct verifier_env *env)
 				continue;
 			}
 
-			if (BPF_MODE(insn->code) != BPF_MEM ||
-			    insn->imm != 0) {
-				verbose("BPF_STX uses reserved fields\n");
-				return -EINVAL;
-			}
 			/* check src1 operand */
 			err = check_reg_arg(regs, insn->src_reg, SRC_OP);
 			if (err)
@@ -1714,6 +1711,8 @@ static int do_check(struct verifier_env *env)
 			if (err)
 				return err;
 
+			dst_reg_type = regs[insn->dst_reg].type;
+
 			/* check that memory (dst_reg + off) is writeable */
 			err = check_mem_access(env, insn->dst_reg, insn->off,
 					       BPF_SIZE(insn->code), BPF_WRITE,
@@ -1721,6 +1720,15 @@ static int do_check(struct verifier_env *env)
 			if (err)
 				return err;
 
+			if (insn->imm == 0) {
+				insn->imm = dst_reg_type;
+			} else if (dst_reg_type != insn->imm &&
+				   (dst_reg_type == PTR_TO_CTX ||
+				    insn->imm == PTR_TO_CTX)) {
+				verbose("same insn cannot be used with different pointers\n");
+				return -EINVAL;
+			}
+
 		} else if (class == BPF_ST) {
 			if (BPF_MODE(insn->code) != BPF_MEM ||
 			    insn->src_reg != BPF_REG_0) {
@@ -1839,12 +1847,18 @@ static int replace_map_fd_with_map_ptr(struct verifier_env *env)
 
 	for (i = 0; i < insn_cnt; i++, insn++) {
 		if (BPF_CLASS(insn->code) == BPF_LDX &&
-		    (BPF_MODE(insn->code) != BPF_MEM ||
-		     insn->imm != 0)) {
+		    (BPF_MODE(insn->code) != BPF_MEM || insn->imm != 0)) {
 			verbose("BPF_LDX uses reserved fields\n");
 			return -EINVAL;
 		}
 
+		if (BPF_CLASS(insn->code) == BPF_STX &&
+		    ((BPF_MODE(insn->code) != BPF_MEM &&
+		      BPF_MODE(insn->code) != BPF_XADD) || insn->imm != 0)) {
+			verbose("BPF_STX uses reserved fields\n");
+			return -EINVAL;
+		}
+
 		if (insn[0].code == (BPF_LD | BPF_IMM | BPF_DW)) {
 			struct bpf_map *map;
 			struct fd f;
@@ -1967,12 +1981,17 @@ static int convert_ctx_accesses(struct verifier_env *env)
 	struct bpf_prog *new_prog;
 	u32 cnt;
 	int i;
+	enum bpf_access_type type;
 
 	if (!env->prog->aux->ops->convert_ctx_access)
 		return 0;
 
 	for (i = 0; i < insn_cnt; i++, insn++) {
-		if (insn->code != (BPF_LDX | BPF_MEM | BPF_W))
+		if (insn->code == (BPF_LDX | BPF_MEM | BPF_W))
+			type = BPF_READ;
+		else if (insn->code == (BPF_STX | BPF_MEM | BPF_W))
+			type = BPF_WRITE;
+		else
 			continue;
 
 		if (insn->imm != PTR_TO_CTX) {
@@ -1982,7 +2001,7 @@ static int convert_ctx_accesses(struct verifier_env *env)
 		}
 
 		cnt = env->prog->aux->ops->
-			convert_ctx_access(insn->dst_reg, insn->src_reg,
+			convert_ctx_access(type, insn->dst_reg, insn->src_reg,
 					   insn->off, insn_buf);
 		if (cnt == 0 || cnt >= ARRAY_SIZE(insn_buf)) {
 			verbose("bpf verifier is misconfigured\n");
diff --git a/net/core/filter.c b/net/core/filter.c
index e76b8ec1b0ac..d271c06bf01f 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -1464,13 +1464,8 @@ tc_cls_act_func_proto(enum bpf_func_id func_id)
 	}
 }
 
-static bool sk_filter_is_valid_access(int off, int size,
-				      enum bpf_access_type type)
+static bool __is_valid_access(int off, int size, enum bpf_access_type type)
 {
-	/* only read is allowed */
-	if (type != BPF_READ)
-		return false;
-
 	/* check bounds */
 	if (off < 0 || off >= sizeof(struct __sk_buff))
 		return false;
@@ -1486,8 +1481,42 @@ static bool sk_filter_is_valid_access(int off, int size,
 	return true;
 }
 
-static u32 sk_filter_convert_ctx_access(int dst_reg, int src_reg, int ctx_off,
-					struct bpf_insn *insn_buf)
+static bool sk_filter_is_valid_access(int off, int size,
+				      enum bpf_access_type type)
+{
+	if (type == BPF_WRITE) {
+		switch (off) {
+		case offsetof(struct __sk_buff, cb[0]) ...
+			offsetof(struct __sk_buff, cb[4]):
+			break;
+		default:
+			return false;
+		}
+	}
+
+	return __is_valid_access(off, size, type);
+}
+
+static bool tc_cls_act_is_valid_access(int off, int size,
+				       enum bpf_access_type type)
+{
+	if (type == BPF_WRITE) {
+		switch (off) {
+		case offsetof(struct __sk_buff, mark):
+		case offsetof(struct __sk_buff, tc_index):
+		case offsetof(struct __sk_buff, cb[0]) ...
+			offsetof(struct __sk_buff, cb[4]):
+			break;
+		default:
+			return false;
+		}
+	}
+	return __is_valid_access(off, size, type);
+}
+
+static u32 bpf_net_convert_ctx_access(enum bpf_access_type type, int dst_reg,
+				      int src_reg, int ctx_off,
+				      struct bpf_insn *insn_buf)
 {
 	struct bpf_insn *insn = insn_buf;
 
@@ -1539,7 +1568,15 @@ static u32 sk_filter_convert_ctx_access(int dst_reg, int src_reg, int ctx_off,
 		break;
 
 	case offsetof(struct __sk_buff, mark):
-		return convert_skb_access(SKF_AD_MARK, dst_reg, src_reg, insn);
+		BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, mark) != 4);
+
+		if (type == BPF_WRITE)
+			*insn++ = BPF_STX_MEM(BPF_W, dst_reg, src_reg,
+					      offsetof(struct sk_buff, mark));
+		else
+			*insn++ = BPF_LDX_MEM(BPF_W, dst_reg, src_reg,
+					      offsetof(struct sk_buff, mark));
+		break;
 
 	case offsetof(struct __sk_buff, pkt_type):
 		return convert_skb_access(SKF_AD_PKTTYPE, dst_reg, src_reg, insn);
@@ -1554,6 +1591,38 @@ static u32 sk_filter_convert_ctx_access(int dst_reg, int src_reg, int ctx_off,
 	case offsetof(struct __sk_buff, vlan_tci):
 		return convert_skb_access(SKF_AD_VLAN_TAG,
 					  dst_reg, src_reg, insn);
+
+	case offsetof(struct __sk_buff, cb[0]) ...
+		offsetof(struct __sk_buff, cb[4]):
+		BUILD_BUG_ON(FIELD_SIZEOF(struct qdisc_skb_cb, data) < 20);
+
+		ctx_off -= offsetof(struct __sk_buff, cb[0]);
+		ctx_off += offsetof(struct sk_buff, cb);
+		ctx_off += offsetof(struct qdisc_skb_cb, data);
+		if (type == BPF_WRITE)
+			*insn++ = BPF_STX_MEM(BPF_W, dst_reg, src_reg, ctx_off);
+		else
+			*insn++ = BPF_LDX_MEM(BPF_W, dst_reg, src_reg, ctx_off);
+		break;
+
+	case offsetof(struct __sk_buff, tc_index):
+#ifdef CONFIG_NET_SCHED
+		BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, tc_index) != 2);
+
+		if (type == BPF_WRITE)
+			*insn++ = BPF_STX_MEM(BPF_H, dst_reg, src_reg,
+					      offsetof(struct sk_buff, tc_index));
+		else
+			*insn++ = BPF_LDX_MEM(BPF_H, dst_reg, src_reg,
+					      offsetof(struct sk_buff, tc_index));
+		break;
+#else
+		if (type == BPF_WRITE)
+			*insn++ = BPF_MOV64_REG(dst_reg, dst_reg);
+		else
+			*insn++ = BPF_MOV64_IMM(dst_reg, 0);
+		break;
+#endif
 	}
 
 	return insn - insn_buf;
@@ -1562,13 +1631,13 @@ static u32 sk_filter_convert_ctx_access(int dst_reg, int src_reg, int ctx_off,
 static const struct bpf_verifier_ops sk_filter_ops = {
 	.get_func_proto = sk_filter_func_proto,
 	.is_valid_access = sk_filter_is_valid_access,
-	.convert_ctx_access = sk_filter_convert_ctx_access,
+	.convert_ctx_access = bpf_net_convert_ctx_access,
 };
 
 static const struct bpf_verifier_ops tc_cls_act_ops = {
 	.get_func_proto = tc_cls_act_func_proto,
-	.is_valid_access = sk_filter_is_valid_access,
-	.convert_ctx_access = sk_filter_convert_ctx_access,
+	.is_valid_access = tc_cls_act_is_valid_access,
+	.convert_ctx_access = bpf_net_convert_ctx_access,
 };
 
 static struct bpf_prog_type_list sk_filter_type __read_mostly = {
diff --git a/samples/bpf/sockex3_kern.c b/samples/bpf/sockex3_kern.c
index 2625b987944f..41ae2fd21b13 100644
--- a/samples/bpf/sockex3_kern.c
+++ b/samples/bpf/sockex3_kern.c
@@ -89,7 +89,6 @@ static inline __u32 ipv6_addr_hash(struct __sk_buff *ctx, __u64 off)
 
 struct globals {
 	struct flow_keys flow;
-	__u32 nhoff;
 };
 
 struct bpf_map_def SEC("maps") percpu_map = {
@@ -139,7 +138,7 @@ static void update_stats(struct __sk_buff *skb, struct globals *g)
 static __always_inline void parse_ip_proto(struct __sk_buff *skb,
 					   struct globals *g, __u32 ip_proto)
 {
-	__u32 nhoff = g->nhoff;
+	__u32 nhoff = skb->cb[0];
 	int poff;
 
 	switch (ip_proto) {
@@ -165,7 +164,7 @@ static __always_inline void parse_ip_proto(struct __sk_buff *skb,
 		if (gre_flags & GRE_SEQ)
 			nhoff += 4;
 
-		g->nhoff = nhoff;
+		skb->cb[0] = nhoff;
 		parse_eth_proto(skb, gre_proto);
 		break;
 	}
@@ -195,7 +194,7 @@ PROG(PARSE_IP)(struct __sk_buff *skb)
 	if (!g)
 		return 0;
 
-	nhoff = g->nhoff;
+	nhoff = skb->cb[0];
 
 	if (unlikely(ip_is_fragment(skb, nhoff)))
 		return 0;
@@ -210,7 +209,7 @@ PROG(PARSE_IP)(struct __sk_buff *skb)
 	verlen = load_byte(skb, nhoff + 0/*offsetof(struct iphdr, ihl)*/);
 	nhoff += (verlen & 0xF) << 2;
 
-	g->nhoff = nhoff;
+	skb->cb[0] = nhoff;
 	parse_ip_proto(skb, g, ip_proto);
 	return 0;
 }
@@ -223,7 +222,7 @@ PROG(PARSE_IPV6)(struct __sk_buff *skb)
 	if (!g)
 		return 0;
 
-	nhoff = g->nhoff;
+	nhoff = skb->cb[0];
 
 	ip_proto = load_byte(skb,
 			     nhoff + offsetof(struct ipv6hdr, nexthdr));
@@ -233,25 +232,21 @@ PROG(PARSE_IPV6)(struct __sk_buff *skb)
 				     nhoff + offsetof(struct ipv6hdr, daddr));
 	nhoff += sizeof(struct ipv6hdr);
 
-	g->nhoff = nhoff;
+	skb->cb[0] = nhoff;
 	parse_ip_proto(skb, g, ip_proto);
 	return 0;
 }
 
 PROG(PARSE_VLAN)(struct __sk_buff *skb)
 {
-	struct globals *g = this_cpu_globals();
 	__u32 nhoff, proto;
 
-	if (!g)
-		return 0;
-
-	nhoff = g->nhoff;
+	nhoff = skb->cb[0];
 
 	proto = load_half(skb, nhoff + offsetof(struct vlan_hdr,
 						h_vlan_encapsulated_proto));
 	nhoff += sizeof(struct vlan_hdr);
-	g->nhoff = nhoff;
+	skb->cb[0] = nhoff;
 
 	parse_eth_proto(skb, proto);
 
@@ -260,17 +255,13 @@ PROG(PARSE_VLAN)(struct __sk_buff *skb)
 
 PROG(PARSE_MPLS)(struct __sk_buff *skb)
 {
-	struct globals *g = this_cpu_globals();
 	__u32 nhoff, label;
 
-	if (!g)
-		return 0;
-
-	nhoff = g->nhoff;
+	nhoff = skb->cb[0];
 
 	label = load_word(skb, nhoff);
 	nhoff += sizeof(struct mpls_label);
-	g->nhoff = nhoff;
+	skb->cb[0] = nhoff;
 
 	if (label & MPLS_LS_S_MASK) {
 		__u8 verlen = load_byte(skb, nhoff);
@@ -288,14 +279,10 @@ PROG(PARSE_MPLS)(struct __sk_buff *skb)
 SEC("socket/0")
 int main_prog(struct __sk_buff *skb)
 {
-	struct globals *g = this_cpu_globals();
 	__u32 nhoff = ETH_HLEN;
 	__u32 proto = load_half(skb, 12);
 
-	if (!g)
-		return 0;
-
-	g->nhoff = nhoff;
+	skb->cb[0] = nhoff;
 	parse_eth_proto(skb, proto);
 	return 0;
 }
diff --git a/samples/bpf/test_verifier.c b/samples/bpf/test_verifier.c
index 12f3780af73f..693605997abc 100644
--- a/samples/bpf/test_verifier.c
+++ b/samples/bpf/test_verifier.c
@@ -29,6 +29,7 @@ struct bpf_test {
 		ACCEPT,
 		REJECT
 	} result;
+	enum bpf_prog_type prog_type;
 };
 
 static struct bpf_test tests[] = {
@@ -743,6 +744,84 @@ static struct bpf_test tests[] = {
 		.errstr = "different pointers",
 		.result = REJECT,
 	},
+	{
+		"check skb->mark is not writeable by sockets",
+		.insns = {
+			BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_1,
+				    offsetof(struct __sk_buff, mark)),
+			BPF_EXIT_INSN(),
+		},
+		.errstr = "invalid bpf_context access",
+		.result = REJECT,
+	},
+	{
+		"check skb->tc_index is not writeable by sockets",
+		.insns = {
+			BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_1,
+				    offsetof(struct __sk_buff, tc_index)),
+			BPF_EXIT_INSN(),
+		},
+		.errstr = "invalid bpf_context access",
+		.result = REJECT,
+	},
+	{
+		"check non-u32 access to cb",
+		.insns = {
+			BPF_STX_MEM(BPF_H, BPF_REG_1, BPF_REG_1,
+				    offsetof(struct __sk_buff, cb[0])),
+			BPF_EXIT_INSN(),
+		},
+		.errstr = "invalid bpf_context access",
+		.result = REJECT,
+	},
+	{
+		"check out of range skb->cb access",
+		.insns = {
+			BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
+				    offsetof(struct __sk_buff, cb[60])),
+			BPF_EXIT_INSN(),
+		},
+		.errstr = "invalid bpf_context access",
+		.result = REJECT,
+		.prog_type = BPF_PROG_TYPE_SCHED_ACT,
+	},
+	{
+		"write skb fields from socket prog",
+		.insns = {
+			BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
+				    offsetof(struct __sk_buff, cb[4])),
+			BPF_JMP_IMM(BPF_JGE, BPF_REG_0, 0, 1),
+			BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
+				    offsetof(struct __sk_buff, mark)),
+			BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
+				    offsetof(struct __sk_buff, tc_index)),
+			BPF_JMP_IMM(BPF_JGE, BPF_REG_0, 0, 1),
+			BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_1,
+				    offsetof(struct __sk_buff, cb[0])),
+			BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_1,
+				    offsetof(struct __sk_buff, cb[2])),
+			BPF_EXIT_INSN(),
+		},
+		.result = ACCEPT,
+	},
+	{
+		"write skb fields from tc_cls_act prog",
+		.insns = {
+			BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
+				    offsetof(struct __sk_buff, cb[0])),
+			BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_0,
+				    offsetof(struct __sk_buff, mark)),
+			BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
+				    offsetof(struct __sk_buff, tc_index)),
+			BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_0,
+				    offsetof(struct __sk_buff, tc_index)),
+			BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_0,
+				    offsetof(struct __sk_buff, cb[3])),
+			BPF_EXIT_INSN(),
+		},
+		.result = ACCEPT,
+		.prog_type = BPF_PROG_TYPE_SCHED_CLS,
+	},
 };
 
 static int probe_filter_length(struct bpf_insn *fp)
@@ -775,6 +854,7 @@ static int test(void)
 
 	for (i = 0; i < ARRAY_SIZE(tests); i++) {
 		struct bpf_insn *prog = tests[i].insns;
+		int prog_type = tests[i].prog_type;
 		int prog_len = probe_filter_length(prog);
 		int *fixup = tests[i].fixup;
 		int map_fd = -1;
@@ -789,8 +869,8 @@ static int test(void)
 		}
 		printf("#%d %s ", i, tests[i].descr);
 
-		prog_fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, prog,
-					prog_len * sizeof(struct bpf_insn),
+		prog_fd = bpf_prog_load(prog_type ?: BPF_PROG_TYPE_SOCKET_FILTER,
+					prog, prog_len * sizeof(struct bpf_insn),
 					"GPL", 0);
 
 		if (tests[i].result == ACCEPT) {
-- 
1.7.9.5

Re: [PATCH net-next 1/2] bpf: make programs see skb->data == L2 for ingress and egress

[David Miller]

From: Alexei Starovoitov <ast@plumgrid.com>
Date: Wed,  3 Jun 2015 22:07:10 -0700

> +	u32 at_ingress = G_TC_AT(skb->tc_verd) & AT_INGRESS;

Please use a 'bool' for this.

> @@ -64,6 +64,7 @@ static int cls_bpf_classify(struct sk_buff *skb, const struct tcf_proto *tp,
>  {
>  	struct cls_bpf_head *head = rcu_dereference_bh(tp->root);
>  	struct cls_bpf_prog *prog;
> +	u32 at_ingress = G_TC_AT(skb->tc_verd) & AT_INGRESS;
>  	int ret = -1;
>  
>  	if (unlikely(!skb_mac_header_was_set(skb)))

Likewise.

Thank you.