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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: Mathieu Xhonneux <m.xhonneux@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Mathieu Xhonneux 2018-07-26 02:10:40 +00:00 committed by Daniel Borkmann
parent 1ce6a9fc15
commit 486cdf2158
3 changed files with 94 additions and 48 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
include/net/seg6_local.h
View File

@ -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);

88
net/core/filter.c
View File

@ -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
};
static void bpf_update_srh_state(struct sk_buff *skb)
{
struct seg6_bpf_srh_state *srh_state =
this_cpu_ptr(&seg6_bpf_srh_states);
int srhoff = 0;
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);
struct ipv6_sr_hdr *srh;
int srhoff = 0;
int hdroff = 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;
}
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;
}

50
net/ipv6/seg6_local.c
View File

@ -459,36 +459,57 @@ drop:
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;
}