tc: bpf: generalize pedit action

existing TC action 'pedit' can munge any bits of the packet.
Generalize it for use in bpf programs attached as cls_bpf and act_bpf via
bpf_skb_store_bytes() helper function.
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Reviewed-by: Jiri Pirko <jiri@resnulli.us>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/bpf.h

@@ -59,6 +59,7 @@ enum bpf_arg_type {
 	ARG_PTR_TO_STACK,	/* any pointer to eBPF program stack */
 	ARG_CONST_STACK_SIZE,	/* number of bytes accessed from stack */
 
+	ARG_PTR_TO_CTX,		/* pointer to context */
 	ARG_ANYTHING,		/* any (initialized) argument is ok */
 };
 

include/uapi/linux/bpf.h

@@ -168,6 +168,7 @@ enum bpf_func_id {
 	BPF_FUNC_map_delete_elem, /* int map_delete_elem(&map, &key) */
 	BPF_FUNC_get_prandom_u32, /* u32 prandom_u32(void) */
 	BPF_FUNC_get_smp_processor_id, /* u32 raw_smp_processor_id(void) */
+	BPF_FUNC_skb_store_bytes, /* int skb_store_bytes(skb, offset, from, len) */
 	__BPF_FUNC_MAX_ID,
 };
 

kernel/bpf/verifier.c

@@ -773,6 +773,8 @@ static int check_func_arg(struct verifier_env *env, u32 regno,
 		expected_type = CONST_IMM;
 	} else if (arg_type == ARG_CONST_MAP_PTR) {
 		expected_type = CONST_PTR_TO_MAP;
+	} else if (arg_type == ARG_PTR_TO_CTX) {
+		expected_type = PTR_TO_CTX;
 	} else {
 		verbose("unsupported arg_type %d\n", arg_type);
 		return -EFAULT;

net/core/filter.c

@@ -1175,6 +1175,56 @@ int sk_attach_bpf(u32 ufd, struct sock *sk)
 	return 0;
 }
 
+static u64 bpf_skb_store_bytes(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
+{
+	struct sk_buff *skb = (struct sk_buff *) (long) r1;
+	unsigned int offset = (unsigned int) r2;
+	void *from = (void *) (long) r3;
+	unsigned int len = (unsigned int) r4;
+	char buf[16];
+	void *ptr;
+
+	/* bpf verifier guarantees that:
+	 * 'from' pointer points to bpf program stack
+	 * 'len' bytes of it were initialized
+	 * 'len' > 0
+	 * 'skb' is a valid pointer to 'struct sk_buff'
+	 *
+	 * so check for invalid 'offset' and too large 'len'
+	 */
+	if (offset > 0xffff || len > sizeof(buf))
+		return -EFAULT;
+
+	if (skb_cloned(skb) && !skb_clone_writable(skb, offset + len))
+		return -EFAULT;
+
+	ptr = skb_header_pointer(skb, offset, len, buf);
+	if (unlikely(!ptr))
+		return -EFAULT;
+
+	skb_postpull_rcsum(skb, ptr, len);
+
+	memcpy(ptr, from, len);
+
+	if (ptr == buf)
+		/* skb_store_bits cannot return -EFAULT here */
+		skb_store_bits(skb, offset, ptr, len);
+
+	if (skb->ip_summed == CHECKSUM_COMPLETE)
+		skb->csum = csum_add(skb->csum, csum_partial(ptr, len, 0));
+	return 0;
+}
+
+const struct bpf_func_proto bpf_skb_store_bytes_proto = {
+	.func		= bpf_skb_store_bytes,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_CTX,
+	.arg2_type	= ARG_ANYTHING,
+	.arg3_type	= ARG_PTR_TO_STACK,
+	.arg4_type	= ARG_CONST_STACK_SIZE,
+};
+
 static const struct bpf_func_proto *
 sk_filter_func_proto(enum bpf_func_id func_id)
 {
@@ -1194,6 +1244,17 @@ sk_filter_func_proto(enum bpf_func_id func_id)
 	}
 }
 
+static const struct bpf_func_proto *
+tc_cls_act_func_proto(enum bpf_func_id func_id)
+{
+	switch (func_id) {
+	case BPF_FUNC_skb_store_bytes:
+		return &bpf_skb_store_bytes_proto;
+	default:
+		return sk_filter_func_proto(func_id);
+	}
+}
+
 static bool sk_filter_is_valid_access(int off, int size,
 				      enum bpf_access_type type)
 {
@@ -1270,18 +1331,24 @@ static const struct bpf_verifier_ops sk_filter_ops = {
 	.convert_ctx_access = sk_filter_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,
+};
+
 static struct bpf_prog_type_list sk_filter_type __read_mostly = {
 	.ops = &sk_filter_ops,
 	.type = BPF_PROG_TYPE_SOCKET_FILTER,
 };
 
 static struct bpf_prog_type_list sched_cls_type __read_mostly = {
-	.ops = &sk_filter_ops,
+	.ops = &tc_cls_act_ops,
 	.type = BPF_PROG_TYPE_SCHED_CLS,
 };
 
 static struct bpf_prog_type_list sched_act_type __read_mostly = {
-	.ops = &sk_filter_ops,
+	.ops = &tc_cls_act_ops,
 	.type = BPF_PROG_TYPE_SCHED_ACT,
 };