1/* Copyright (c) 2016 Thomas Graf <tgraf@tgraf.ch>
  2 *
  3 * This program is free software; you can redistribute it and/or
  4 * modify it under the terms of version 2 of the GNU General Public
  5 * License as published by the Free Software Foundation.
  6 *
  7 * This program is distributed in the hope that it will be useful, but
  8 * WITHOUT ANY WARRANTY; without even the implied warranty of
  9 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 10 * General Public License for more details.
 11 */
 12
 13#include <linux/kernel.h>
 14#include <linux/module.h>
 15#include <linux/skbuff.h>
 16#include <linux/types.h>
 17#include <linux/bpf.h>
 18#include <net/lwtunnel.h>
 19
 20struct bpf_lwt_prog {
 21	struct bpf_prog *prog;
 22	char *name;
 23};
 24
 25struct bpf_lwt {
 26	struct bpf_lwt_prog in;
 27	struct bpf_lwt_prog out;
 28	struct bpf_lwt_prog xmit;
 29	int family;
 30};
 31
 32#define MAX_PROG_NAME 256
 33
 34static inline struct bpf_lwt *bpf_lwt_lwtunnel(struct lwtunnel_state *lwt)
 35{
 36	return (struct bpf_lwt *)lwt->data;
 37}
 38
 39#define NO_REDIRECT false
 40#define CAN_REDIRECT true
 41
 42static int run_lwt_bpf(struct sk_buff *skb, struct bpf_lwt_prog *lwt,
 43		       struct dst_entry *dst, bool can_redirect)
 44{
 45	int ret;
 46
 47	/* Preempt disable is needed to protect per-cpu redirect_info between
 48	 * BPF prog and skb_do_redirect(). The call_rcu in bpf_prog_put() and
 49	 * access to maps strictly require a rcu_read_lock() for protection,
 50	 * mixing with BH RCU lock doesn't work.
 51	 */
 52	preempt_disable();
 53	rcu_read_lock();
 54	bpf_compute_data_end(skb);
 55	ret = bpf_prog_run_save_cb(lwt->prog, skb);
 56	rcu_read_unlock();
 57
 58	switch (ret) {
 59	case BPF_OK:
 60		break;
 61
 62	case BPF_REDIRECT:
 63		if (unlikely(!can_redirect)) {
 64			pr_warn_once("Illegal redirect return code in prog %s\n",
 65				     lwt->name ? : "<unknown>");
 66			ret = BPF_OK;
 67		} else {
 68			ret = skb_do_redirect(skb);
 69			if (ret == 0)
 70				ret = BPF_REDIRECT;
 71		}
 72		break;
 73
 74	case BPF_DROP:
 75		kfree_skb(skb);
 76		ret = -EPERM;
 77		break;
 78
 79	default:
 80		pr_warn_once("bpf-lwt: Illegal return value %u, expect packet loss\n", ret);
 81		kfree_skb(skb);
 82		ret = -EINVAL;
 83		break;
 84	}
 85
 86	preempt_enable();
 87
 88	return ret;
 89}
 90
 91static int bpf_input(struct sk_buff *skb)
 92{
 93	struct dst_entry *dst = skb_dst(skb);
 94	struct bpf_lwt *bpf;
 95	int ret;
 96
 97	bpf = bpf_lwt_lwtunnel(dst->lwtstate);
 98	if (bpf->in.prog) {
 99		ret = run_lwt_bpf(skb, &bpf->in, dst, NO_REDIRECT);
100		if (ret < 0)
101			return ret;
102	}
103
104	if (unlikely(!dst->lwtstate->orig_input)) {
105		pr_warn_once("orig_input not set on dst for prog %s\n",
106			     bpf->out.name);
107		kfree_skb(skb);
108		return -EINVAL;
109	}
110
111	return dst->lwtstate->orig_input(skb);
112}
113
114static int bpf_output(struct net *net, struct sock *sk, struct sk_buff *skb)
115{
116	struct dst_entry *dst = skb_dst(skb);
117	struct bpf_lwt *bpf;
118	int ret;
119
120	bpf = bpf_lwt_lwtunnel(dst->lwtstate);
121	if (bpf->out.prog) {
122		ret = run_lwt_bpf(skb, &bpf->out, dst, NO_REDIRECT);
123		if (ret < 0)
124			return ret;
125	}
126
127	if (unlikely(!dst->lwtstate->orig_output)) {
128		pr_warn_once("orig_output not set on dst for prog %s\n",
129			     bpf->out.name);
130		kfree_skb(skb);
131		return -EINVAL;
132	}
133
134	return dst->lwtstate->orig_output(net, sk, skb);
135}
136
137static int xmit_check_hhlen(struct sk_buff *skb)
138{
139	int hh_len = skb_dst(skb)->dev->hard_header_len;
140
141	if (skb_headroom(skb) < hh_len) {
142		int nhead = HH_DATA_ALIGN(hh_len - skb_headroom(skb));
143
144		if (pskb_expand_head(skb, nhead, 0, GFP_ATOMIC))
145			return -ENOMEM;
146	}
147
148	return 0;
149}
150
151static int bpf_xmit(struct sk_buff *skb)
152{
153	struct dst_entry *dst = skb_dst(skb);
154	struct bpf_lwt *bpf;
155
156	bpf = bpf_lwt_lwtunnel(dst->lwtstate);
157	if (bpf->xmit.prog) {
158		int ret;
159
160		ret = run_lwt_bpf(skb, &bpf->xmit, dst, CAN_REDIRECT);
161		switch (ret) {
162		case BPF_OK:
163			/* If the header was expanded, headroom might be too
164			 * small for L2 header to come, expand as needed.
165			 */
166			ret = xmit_check_hhlen(skb);
167			if (unlikely(ret))
168				return ret;
169
170			return LWTUNNEL_XMIT_CONTINUE;
171		case BPF_REDIRECT:
172			return LWTUNNEL_XMIT_DONE;
173		default:
174			return ret;
175		}
176	}
177
178	return LWTUNNEL_XMIT_CONTINUE;
179}
180
181static void bpf_lwt_prog_destroy(struct bpf_lwt_prog *prog)
182{
183	if (prog->prog)
184		bpf_prog_put(prog->prog);
185
186	kfree(prog->name);
187}
188
189static void bpf_destroy_state(struct lwtunnel_state *lwt)
190{
191	struct bpf_lwt *bpf = bpf_lwt_lwtunnel(lwt);
192
193	bpf_lwt_prog_destroy(&bpf->in);
194	bpf_lwt_prog_destroy(&bpf->out);
195	bpf_lwt_prog_destroy(&bpf->xmit);
196}
197
198static const struct nla_policy bpf_prog_policy[LWT_BPF_PROG_MAX + 1] = {
199	[LWT_BPF_PROG_FD]   = { .type = NLA_U32, },
200	[LWT_BPF_PROG_NAME] = { .type = NLA_NUL_STRING,
201				.len = MAX_PROG_NAME },
202};
203
204static int bpf_parse_prog(struct nlattr *attr, struct bpf_lwt_prog *prog,
205			  enum bpf_prog_type type)
206{
207	struct nlattr *tb[LWT_BPF_PROG_MAX + 1];
208	struct bpf_prog *p;
209	int ret;
210	u32 fd;
211
212	ret = nla_parse_nested(tb, LWT_BPF_PROG_MAX, attr, bpf_prog_policy);
213	if (ret < 0)
214		return ret;
215
216	if (!tb[LWT_BPF_PROG_FD] || !tb[LWT_BPF_PROG_NAME])
217		return -EINVAL;
218
219	prog->name = nla_memdup(tb[LWT_BPF_PROG_NAME], GFP_KERNEL);
220	if (!prog->name)
221		return -ENOMEM;
222
223	fd = nla_get_u32(tb[LWT_BPF_PROG_FD]);
224	p = bpf_prog_get_type(fd, type);
225	if (IS_ERR(p))
226		return PTR_ERR(p);
227
228	prog->prog = p;
229
230	return 0;
231}
232
233static const struct nla_policy bpf_nl_policy[LWT_BPF_MAX + 1] = {
234	[LWT_BPF_IN]		= { .type = NLA_NESTED, },
235	[LWT_BPF_OUT]		= { .type = NLA_NESTED, },
236	[LWT_BPF_XMIT]		= { .type = NLA_NESTED, },
237	[LWT_BPF_XMIT_HEADROOM]	= { .type = NLA_U32 },
238};
239
240static int bpf_build_state(struct net_device *dev, struct nlattr *nla,
241			   unsigned int family, const void *cfg,
242			   struct lwtunnel_state **ts)
243{
244	struct nlattr *tb[LWT_BPF_MAX + 1];
245	struct lwtunnel_state *newts;
246	struct bpf_lwt *bpf;
247	int ret;
248
249	if (family != AF_INET && family != AF_INET6)
250		return -EAFNOSUPPORT;
251
252	ret = nla_parse_nested(tb, LWT_BPF_MAX, nla, bpf_nl_policy);
253	if (ret < 0)
254		return ret;
255
256	if (!tb[LWT_BPF_IN] && !tb[LWT_BPF_OUT] && !tb[LWT_BPF_XMIT])
257		return -EINVAL;
258
259	newts = lwtunnel_state_alloc(sizeof(*bpf));
260	if (!newts)
261		return -ENOMEM;
262
263	newts->type = LWTUNNEL_ENCAP_BPF;
264	bpf = bpf_lwt_lwtunnel(newts);
265
266	if (tb[LWT_BPF_IN]) {
267		newts->flags |= LWTUNNEL_STATE_INPUT_REDIRECT;
268		ret = bpf_parse_prog(tb[LWT_BPF_IN], &bpf->in,
269				     BPF_PROG_TYPE_LWT_IN);
270		if (ret  < 0)
271			goto errout;
272	}
273
274	if (tb[LWT_BPF_OUT]) {
275		newts->flags |= LWTUNNEL_STATE_OUTPUT_REDIRECT;
276		ret = bpf_parse_prog(tb[LWT_BPF_OUT], &bpf->out,
277				     BPF_PROG_TYPE_LWT_OUT);
278		if (ret < 0)
279			goto errout;
280	}
281
282	if (tb[LWT_BPF_XMIT]) {
283		newts->flags |= LWTUNNEL_STATE_XMIT_REDIRECT;
284		ret = bpf_parse_prog(tb[LWT_BPF_XMIT], &bpf->xmit,
285				     BPF_PROG_TYPE_LWT_XMIT);
286		if (ret < 0)
287			goto errout;
288	}
289
290	if (tb[LWT_BPF_XMIT_HEADROOM]) {
291		u32 headroom = nla_get_u32(tb[LWT_BPF_XMIT_HEADROOM]);
292
293		if (headroom > LWT_BPF_MAX_HEADROOM) {
294			ret = -ERANGE;
295			goto errout;
296		}
297
298		newts->headroom = headroom;
299	}
300
301	bpf->family = family;
302	*ts = newts;
303
304	return 0;
305
306errout:
307	bpf_destroy_state(newts);
308	kfree(newts);
309	return ret;
310}
311
312static int bpf_fill_lwt_prog(struct sk_buff *skb, int attr,
313			     struct bpf_lwt_prog *prog)
314{
315	struct nlattr *nest;
316
317	if (!prog->prog)
318		return 0;
319
320	nest = nla_nest_start(skb, attr);
321	if (!nest)
322		return -EMSGSIZE;
323
324	if (prog->name &&
325	    nla_put_string(skb, LWT_BPF_PROG_NAME, prog->name))
326		return -EMSGSIZE;
327
328	return nla_nest_end(skb, nest);
329}
330
331static int bpf_fill_encap_info(struct sk_buff *skb, struct lwtunnel_state *lwt)
332{
333	struct bpf_lwt *bpf = bpf_lwt_lwtunnel(lwt);
334
335	if (bpf_fill_lwt_prog(skb, LWT_BPF_IN, &bpf->in) < 0 ||
336	    bpf_fill_lwt_prog(skb, LWT_BPF_OUT, &bpf->out) < 0 ||
337	    bpf_fill_lwt_prog(skb, LWT_BPF_XMIT, &bpf->xmit) < 0)
338		return -EMSGSIZE;
339
340	return 0;
341}
342
343static int bpf_encap_nlsize(struct lwtunnel_state *lwtstate)
344{
345	int nest_len = nla_total_size(sizeof(struct nlattr)) +
346		       nla_total_size(MAX_PROG_NAME) + /* LWT_BPF_PROG_NAME */
347		       0;
348
349	return nest_len + /* LWT_BPF_IN */
350	       nest_len + /* LWT_BPF_OUT */
351	       nest_len + /* LWT_BPF_XMIT */
352	       0;
353}
354
355int bpf_lwt_prog_cmp(struct bpf_lwt_prog *a, struct bpf_lwt_prog *b)
356{
357	/* FIXME:
358	 * The LWT state is currently rebuilt for delete requests which
359	 * results in a new bpf_prog instance. Comparing names for now.
360	 */
361	if (!a->name && !b->name)
362		return 0;
363
364	if (!a->name || !b->name)
365		return 1;
366
367	return strcmp(a->name, b->name);
368}
369
370static int bpf_encap_cmp(struct lwtunnel_state *a, struct lwtunnel_state *b)
371{
372	struct bpf_lwt *a_bpf = bpf_lwt_lwtunnel(a);
373	struct bpf_lwt *b_bpf = bpf_lwt_lwtunnel(b);
374
375	return bpf_lwt_prog_cmp(&a_bpf->in, &b_bpf->in) ||
376	       bpf_lwt_prog_cmp(&a_bpf->out, &b_bpf->out) ||
377	       bpf_lwt_prog_cmp(&a_bpf->xmit, &b_bpf->xmit);
378}
379
380static const struct lwtunnel_encap_ops bpf_encap_ops = {
381	.build_state	= bpf_build_state,
382	.destroy_state	= bpf_destroy_state,
383	.input		= bpf_input,
384	.output		= bpf_output,
385	.xmit		= bpf_xmit,
386	.fill_encap	= bpf_fill_encap_info,
387	.get_encap_size = bpf_encap_nlsize,
388	.cmp_encap	= bpf_encap_cmp,
389	.owner		= THIS_MODULE,
390};
391
392static int __init bpf_lwt_init(void)
393{
394	return lwtunnel_encap_add_ops(&bpf_encap_ops, LWTUNNEL_ENCAP_BPF);
395}
396
397subsys_initcall(bpf_lwt_init)