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Commit 486cdf21 authored by Mathieu Xhonneux's avatar Mathieu Xhonneux Committed by Daniel Borkmann
Browse files

bpf: add End.DT6 action to bpf_lwt_seg6_action helper 

The seg6local LWT provides the End.DT6 action, which allows to
decapsulate an outer IPv6 header containing a Segment Routing Header
(SRH), full specification is available here:

https://tools.ietf.org/html/draft-filsfils-spring-srv6-network-programming-05



This patch adds this action now to the seg6local BPF
interface. Since it is not mandatory that the inner IPv6 header also
contains a SRH, seg6_bpf_srh_state has been extended with a pointer to
a possible SRH of the outermost IPv6 header. This helps assessing if the
validation must be triggered or not, and avoids some calls to
ipv6_find_hdr.

v3: s/1/true, s/0/false for boolean values
v2: - changed true/false -> 1/0
    - preempt_enable no longer called in first conditional block

Signed-off-by: default avatarMathieu Xhonneux <m.xhonneux@gmail.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent 1ce6a9fc

include/net/seg6_local.h

+3 −1
Original line number Diff line number Diff line
@@ -21,10 +21,12 @@ 


extern int seg6_lookup_nexthop(struct sk_buff *skb, struct in6_addr *nhaddr,

			       u32 tbl_id);

extern bool seg6_bpf_has_valid_srh(struct sk_buff *skb);



struct seg6_bpf_srh_state {

	bool valid;

	struct ipv6_sr_hdr *srh;

	u16 hdrlen;

	bool valid;

};



DECLARE_PER_CPU(struct seg6_bpf_srh_state, seg6_bpf_srh_states);

net/core/filter.c

+59 −29
Original line number Diff line number Diff line
@@ -4542,26 +4542,28 @@ BPF_CALL_4(bpf_lwt_seg6_store_bytes, struct sk_buff *, skb, u32, offset, 
{

	struct seg6_bpf_srh_state *srh_state =

		this_cpu_ptr(&seg6_bpf_srh_states);

	struct ipv6_sr_hdr *srh = srh_state->srh;

	void *srh_tlvs, *srh_end, *ptr;

	struct ipv6_sr_hdr *srh;

	int srhoff = 0;



	if (ipv6_find_hdr(skb, &srhoff, IPPROTO_ROUTING, NULL, NULL) < 0)

	if (srh == NULL)

		return -EINVAL;



	srh = (struct ipv6_sr_hdr *)(skb->data + srhoff);

	srh_tlvs = (void *)((char *)srh + ((srh->first_segment + 1) << 4));

	srh_end = (void *)((char *)srh + sizeof(*srh) + srh_state->hdrlen);



	ptr = skb->data + offset;

	if (ptr >= srh_tlvs && ptr + len <= srh_end)

		srh_state->valid = 0;

		srh_state->valid = false;

	else if (ptr < (void *)&srh->flags ||

		 ptr + len > (void *)&srh->segments)

		return -EFAULT;



	if (unlikely(bpf_try_make_writable(skb, offset + len)))

		return -EFAULT;

	if (ipv6_find_hdr(skb, &srhoff, IPPROTO_ROUTING, NULL, NULL) < 0)

		return -EINVAL;

	srh_state->srh = (struct ipv6_sr_hdr *)(skb->data + srhoff);



	memcpy(skb->data + offset, from, len);

	return 0;
@@ -4577,52 +4579,78 @@ static const struct bpf_func_proto bpf_lwt_seg6_store_bytes_proto = { 
	.arg4_type	= ARG_CONST_SIZE

};



BPF_CALL_4(bpf_lwt_seg6_action, struct sk_buff *, skb,

	   u32, action, void *, param, u32, param_len)

static void bpf_update_srh_state(struct sk_buff *skb)

{

	struct seg6_bpf_srh_state *srh_state =

		this_cpu_ptr(&seg6_bpf_srh_states);

	struct ipv6_sr_hdr *srh;

	int srhoff = 0;

	int err;



	if (ipv6_find_hdr(skb, &srhoff, IPPROTO_ROUTING, NULL, NULL) < 0)

		return -EINVAL;

	srh = (struct ipv6_sr_hdr *)(skb->data + srhoff);



	if (!srh_state->valid) {

		if (unlikely((srh_state->hdrlen & 7) != 0))

			return -EBADMSG;



		srh->hdrlen = (u8)(srh_state->hdrlen >> 3);

		if (unlikely(!seg6_validate_srh(srh, (srh->hdrlen + 1) << 3)))

			return -EBADMSG;



		srh_state->valid = 1;

	if (ipv6_find_hdr(skb, &srhoff, IPPROTO_ROUTING, NULL, NULL) < 0) {

		srh_state->srh = NULL;

	} else {

		srh_state->srh = (struct ipv6_sr_hdr *)(skb->data + srhoff);

		srh_state->hdrlen = srh_state->srh->hdrlen << 3;

		srh_state->valid = true;

	}

}



BPF_CALL_4(bpf_lwt_seg6_action, struct sk_buff *, skb,

	   u32, action, void *, param, u32, param_len)

{

	struct seg6_bpf_srh_state *srh_state =

		this_cpu_ptr(&seg6_bpf_srh_states);

	int hdroff = 0;

	int err;



	switch (action) {

	case SEG6_LOCAL_ACTION_END_X:

		if (!seg6_bpf_has_valid_srh(skb))

			return -EBADMSG;

		if (param_len != sizeof(struct in6_addr))

			return -EINVAL;

		return seg6_lookup_nexthop(skb, (struct in6_addr *)param, 0);

	case SEG6_LOCAL_ACTION_END_T:

		if (!seg6_bpf_has_valid_srh(skb))

			return -EBADMSG;

		if (param_len != sizeof(int))

			return -EINVAL;

		return seg6_lookup_nexthop(skb, NULL, *(int *)param);

	case SEG6_LOCAL_ACTION_END_DT6:

		if (!seg6_bpf_has_valid_srh(skb))

			return -EBADMSG;

		if (param_len != sizeof(int))

			return -EINVAL;



		if (ipv6_find_hdr(skb, &hdroff, IPPROTO_IPV6, NULL, NULL) < 0)

			return -EBADMSG;

		if (!pskb_pull(skb, hdroff))

			return -EBADMSG;



		skb_postpull_rcsum(skb, skb_network_header(skb), hdroff);

		skb_reset_network_header(skb);

		skb_reset_transport_header(skb);

		skb->encapsulation = 0;



		bpf_compute_data_pointers(skb);

		bpf_update_srh_state(skb);

		return seg6_lookup_nexthop(skb, NULL, *(int *)param);

	case SEG6_LOCAL_ACTION_END_B6:

		if (srh_state->srh && !seg6_bpf_has_valid_srh(skb))

			return -EBADMSG;

		err = bpf_push_seg6_encap(skb, BPF_LWT_ENCAP_SEG6_INLINE,

					  param, param_len);

		if (!err)

			srh_state->hdrlen =

				((struct ipv6_sr_hdr *)param)->hdrlen << 3;

			bpf_update_srh_state(skb);



		return err;

	case SEG6_LOCAL_ACTION_END_B6_ENCAP:

		if (srh_state->srh && !seg6_bpf_has_valid_srh(skb))

			return -EBADMSG;

		err = bpf_push_seg6_encap(skb, BPF_LWT_ENCAP_SEG6,

					  param, param_len);

		if (!err)

			srh_state->hdrlen =

				((struct ipv6_sr_hdr *)param)->hdrlen << 3;

			bpf_update_srh_state(skb);



		return err;

	default:

		return -EINVAL;
@@ -4644,15 +4672,14 @@ BPF_CALL_3(bpf_lwt_seg6_adjust_srh, struct sk_buff *, skb, u32, offset, 
{

	struct seg6_bpf_srh_state *srh_state =

		this_cpu_ptr(&seg6_bpf_srh_states);

	struct ipv6_sr_hdr *srh = srh_state->srh;

	void *srh_end, *srh_tlvs, *ptr;

	struct ipv6_sr_hdr *srh;

	struct ipv6hdr *hdr;

	int srhoff = 0;

	int ret;



	if (ipv6_find_hdr(skb, &srhoff, IPPROTO_ROUTING, NULL, NULL) < 0)

	if (unlikely(srh == NULL))

		return -EINVAL;

	srh = (struct ipv6_sr_hdr *)(skb->data + srhoff);



	srh_tlvs = (void *)((unsigned char *)srh + sizeof(*srh) +

			((srh->first_segment + 1) << 4));
@@ -4682,8 +4709,11 @@ BPF_CALL_3(bpf_lwt_seg6_adjust_srh, struct sk_buff *, skb, u32, offset, 
	hdr = (struct ipv6hdr *)skb->data;

	hdr->payload_len = htons(skb->len - sizeof(struct ipv6hdr));



	if (ipv6_find_hdr(skb, &srhoff, IPPROTO_ROUTING, NULL, NULL) < 0)

		return -EINVAL;

	srh_state->srh = (struct ipv6_sr_hdr *)(skb->data + srhoff);

	srh_state->hdrlen += len;

	srh_state->valid = 0;

	srh_state->valid = false;

	return 0;

}

net/ipv6/seg6_local.c

+32 −18
Original line number Diff line number Diff line
@@ -459,36 +459,57 @@ static int input_action_end_b6_encap(struct sk_buff *skb, 


DEFINE_PER_CPU(struct seg6_bpf_srh_state, seg6_bpf_srh_states);



bool seg6_bpf_has_valid_srh(struct sk_buff *skb)

{

	struct seg6_bpf_srh_state *srh_state =

		this_cpu_ptr(&seg6_bpf_srh_states);

	struct ipv6_sr_hdr *srh = srh_state->srh;



	if (unlikely(srh == NULL))

		return false;



	if (unlikely(!srh_state->valid)) {

		if ((srh_state->hdrlen & 7) != 0)

			return false;



		srh->hdrlen = (u8)(srh_state->hdrlen >> 3);

		if (!seg6_validate_srh(srh, (srh->hdrlen + 1) << 3))

			return false;



		srh_state->valid = true;

	}



	return true;

}



static int input_action_end_bpf(struct sk_buff *skb,

				struct seg6_local_lwt *slwt)

{

	struct seg6_bpf_srh_state *srh_state =

		this_cpu_ptr(&seg6_bpf_srh_states);

	struct seg6_bpf_srh_state local_srh_state;

	struct ipv6_sr_hdr *srh;

	int srhoff = 0;

	int ret;



	srh = get_and_validate_srh(skb);

	if (!srh)

		goto drop;

	if (!srh) {

		kfree_skb(skb);

		return -EINVAL;

	}

	advance_nextseg(srh, &ipv6_hdr(skb)->daddr);



	/* preempt_disable is needed to protect the per-CPU buffer srh_state,

	 * which is also accessed by the bpf_lwt_seg6_* helpers

	 */

	preempt_disable();

	srh_state->srh = srh;

	srh_state->hdrlen = srh->hdrlen << 3;

	srh_state->valid = 1;

	srh_state->valid = true;



	rcu_read_lock();

	bpf_compute_data_pointers(skb);

	ret = bpf_prog_run_save_cb(slwt->bpf.prog, skb);

	rcu_read_unlock();



	local_srh_state = *srh_state;

	preempt_enable();



	switch (ret) {

	case BPF_OK:

	case BPF_REDIRECT:
@@ -500,24 +521,17 @@ static int input_action_end_bpf(struct sk_buff *skb, 
		goto drop;

	}



	if (unlikely((local_srh_state.hdrlen & 7) != 0))

		goto drop;



	if (ipv6_find_hdr(skb, &srhoff, IPPROTO_ROUTING, NULL, NULL) < 0)

		goto drop;

	srh = (struct ipv6_sr_hdr *)(skb->data + srhoff);

	srh->hdrlen = (u8)(local_srh_state.hdrlen >> 3);



	if (!local_srh_state.valid &&

	    unlikely(!seg6_validate_srh(srh, (srh->hdrlen + 1) << 3)))

	if (srh_state->srh && !seg6_bpf_has_valid_srh(skb))

		goto drop;



	preempt_enable();

	if (ret != BPF_REDIRECT)

		seg6_lookup_nexthop(skb, NULL, 0);



	return dst_input(skb);



drop:

	preempt_enable();

	kfree_skb(skb);

	return -EINVAL;

}