3e85437f710608ca78db3d5645cf42ac45fee801
[muen/linux.git] / net / core / lwt_bpf.c
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
20 struct bpf_lwt_prog {
21         struct bpf_prog *prog;
22         char *name;
23 };
24
25 struct 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
34 static 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
42 static 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         bpf_compute_data_pointers(skb);
54         ret = bpf_prog_run_save_cb(lwt->prog, skb);
55
56         switch (ret) {
57         case BPF_OK:
58                 break;
59
60         case BPF_REDIRECT:
61                 if (unlikely(!can_redirect)) {
62                         pr_warn_once("Illegal redirect return code in prog %s\n",
63                                      lwt->name ? : "<unknown>");
64                         ret = BPF_OK;
65                 } else {
66                         ret = skb_do_redirect(skb);
67                         if (ret == 0)
68                                 ret = BPF_REDIRECT;
69                 }
70                 break;
71
72         case BPF_DROP:
73                 kfree_skb(skb);
74                 ret = -EPERM;
75                 break;
76
77         default:
78                 pr_warn_once("bpf-lwt: Illegal return value %u, expect packet loss\n", ret);
79                 kfree_skb(skb);
80                 ret = -EINVAL;
81                 break;
82         }
83
84         preempt_enable();
85
86         return ret;
87 }
88
89 static int bpf_input(struct sk_buff *skb)
90 {
91         struct dst_entry *dst = skb_dst(skb);
92         struct bpf_lwt *bpf;
93         int ret;
94
95         bpf = bpf_lwt_lwtunnel(dst->lwtstate);
96         if (bpf->in.prog) {
97                 ret = run_lwt_bpf(skb, &bpf->in, dst, NO_REDIRECT);
98                 if (ret < 0)
99                         return ret;
100         }
101
102         if (unlikely(!dst->lwtstate->orig_input)) {
103                 pr_warn_once("orig_input not set on dst for prog %s\n",
104                              bpf->out.name);
105                 kfree_skb(skb);
106                 return -EINVAL;
107         }
108
109         return dst->lwtstate->orig_input(skb);
110 }
111
112 static int bpf_output(struct net *net, struct sock *sk, struct sk_buff *skb)
113 {
114         struct dst_entry *dst = skb_dst(skb);
115         struct bpf_lwt *bpf;
116         int ret;
117
118         bpf = bpf_lwt_lwtunnel(dst->lwtstate);
119         if (bpf->out.prog) {
120                 ret = run_lwt_bpf(skb, &bpf->out, dst, NO_REDIRECT);
121                 if (ret < 0)
122                         return ret;
123         }
124
125         if (unlikely(!dst->lwtstate->orig_output)) {
126                 pr_warn_once("orig_output not set on dst for prog %s\n",
127                              bpf->out.name);
128                 kfree_skb(skb);
129                 return -EINVAL;
130         }
131
132         return dst->lwtstate->orig_output(net, sk, skb);
133 }
134
135 static int xmit_check_hhlen(struct sk_buff *skb)
136 {
137         int hh_len = skb_dst(skb)->dev->hard_header_len;
138
139         if (skb_headroom(skb) < hh_len) {
140                 int nhead = HH_DATA_ALIGN(hh_len - skb_headroom(skb));
141
142                 if (pskb_expand_head(skb, nhead, 0, GFP_ATOMIC))
143                         return -ENOMEM;
144         }
145
146         return 0;
147 }
148
149 static int bpf_xmit(struct sk_buff *skb)
150 {
151         struct dst_entry *dst = skb_dst(skb);
152         struct bpf_lwt *bpf;
153
154         bpf = bpf_lwt_lwtunnel(dst->lwtstate);
155         if (bpf->xmit.prog) {
156                 int ret;
157
158                 ret = run_lwt_bpf(skb, &bpf->xmit, dst, CAN_REDIRECT);
159                 switch (ret) {
160                 case BPF_OK:
161                         /* If the header was expanded, headroom might be too
162                          * small for L2 header to come, expand as needed.
163                          */
164                         ret = xmit_check_hhlen(skb);
165                         if (unlikely(ret))
166                                 return ret;
167
168                         return LWTUNNEL_XMIT_CONTINUE;
169                 case BPF_REDIRECT:
170                         return LWTUNNEL_XMIT_DONE;
171                 default:
172                         return ret;
173                 }
174         }
175
176         return LWTUNNEL_XMIT_CONTINUE;
177 }
178
179 static void bpf_lwt_prog_destroy(struct bpf_lwt_prog *prog)
180 {
181         if (prog->prog)
182                 bpf_prog_put(prog->prog);
183
184         kfree(prog->name);
185 }
186
187 static void bpf_destroy_state(struct lwtunnel_state *lwt)
188 {
189         struct bpf_lwt *bpf = bpf_lwt_lwtunnel(lwt);
190
191         bpf_lwt_prog_destroy(&bpf->in);
192         bpf_lwt_prog_destroy(&bpf->out);
193         bpf_lwt_prog_destroy(&bpf->xmit);
194 }
195
196 static const struct nla_policy bpf_prog_policy[LWT_BPF_PROG_MAX + 1] = {
197         [LWT_BPF_PROG_FD]   = { .type = NLA_U32, },
198         [LWT_BPF_PROG_NAME] = { .type = NLA_NUL_STRING,
199                                 .len = MAX_PROG_NAME },
200 };
201
202 static int bpf_parse_prog(struct nlattr *attr, struct bpf_lwt_prog *prog,
203                           enum bpf_prog_type type)
204 {
205         struct nlattr *tb[LWT_BPF_PROG_MAX + 1];
206         struct bpf_prog *p;
207         int ret;
208         u32 fd;
209
210         ret = nla_parse_nested(tb, LWT_BPF_PROG_MAX, attr, bpf_prog_policy,
211                                NULL);
212         if (ret < 0)
213                 return ret;
214
215         if (!tb[LWT_BPF_PROG_FD] || !tb[LWT_BPF_PROG_NAME])
216                 return -EINVAL;
217
218         prog->name = nla_memdup(tb[LWT_BPF_PROG_NAME], GFP_ATOMIC);
219         if (!prog->name)
220                 return -ENOMEM;
221
222         fd = nla_get_u32(tb[LWT_BPF_PROG_FD]);
223         p = bpf_prog_get_type(fd, type);
224         if (IS_ERR(p))
225                 return PTR_ERR(p);
226
227         prog->prog = p;
228
229         return 0;
230 }
231
232 static const struct nla_policy bpf_nl_policy[LWT_BPF_MAX + 1] = {
233         [LWT_BPF_IN]            = { .type = NLA_NESTED, },
234         [LWT_BPF_OUT]           = { .type = NLA_NESTED, },
235         [LWT_BPF_XMIT]          = { .type = NLA_NESTED, },
236         [LWT_BPF_XMIT_HEADROOM] = { .type = NLA_U32 },
237 };
238
239 static int bpf_build_state(struct nlattr *nla,
240                            unsigned int family, const void *cfg,
241                            struct lwtunnel_state **ts,
242                            struct netlink_ext_ack *extack)
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, extack);
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
306 errout:
307         bpf_destroy_state(newts);
308         kfree(newts);
309         return ret;
310 }
311
312 static 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
331 static 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
343 static 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
355 static int 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
370 static 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
380 static 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
392 static int __init bpf_lwt_init(void)
393 {
394         return lwtunnel_encap_add_ops(&bpf_encap_ops, LWTUNNEL_ENCAP_BPF);
395 }
396
397 subsys_initcall(bpf_lwt_init)