bpf: in __bpf_redirect_no_mac pull mac only if present
[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                         skb_reset_mac_header(skb);
67                         ret = skb_do_redirect(skb);
68                         if (ret == 0)
69                                 ret = BPF_REDIRECT;
70                 }
71                 break;
72
73         case BPF_DROP:
74                 kfree_skb(skb);
75                 ret = -EPERM;
76                 break;
77
78         default:
79                 pr_warn_once("bpf-lwt: Illegal return value %u, expect packet loss\n", ret);
80                 kfree_skb(skb);
81                 ret = -EINVAL;
82                 break;
83         }
84
85         preempt_enable();
86
87         return ret;
88 }
89
90 static int bpf_input(struct sk_buff *skb)
91 {
92         struct dst_entry *dst = skb_dst(skb);
93         struct bpf_lwt *bpf;
94         int ret;
95
96         bpf = bpf_lwt_lwtunnel(dst->lwtstate);
97         if (bpf->in.prog) {
98                 ret = run_lwt_bpf(skb, &bpf->in, dst, NO_REDIRECT);
99                 if (ret < 0)
100                         return ret;
101         }
102
103         if (unlikely(!dst->lwtstate->orig_input)) {
104                 pr_warn_once("orig_input not set on dst for prog %s\n",
105                              bpf->out.name);
106                 kfree_skb(skb);
107                 return -EINVAL;
108         }
109
110         return dst->lwtstate->orig_input(skb);
111 }
112
113 static int bpf_output(struct net *net, struct sock *sk, struct sk_buff *skb)
114 {
115         struct dst_entry *dst = skb_dst(skb);
116         struct bpf_lwt *bpf;
117         int ret;
118
119         bpf = bpf_lwt_lwtunnel(dst->lwtstate);
120         if (bpf->out.prog) {
121                 ret = run_lwt_bpf(skb, &bpf->out, dst, NO_REDIRECT);
122                 if (ret < 0)
123                         return ret;
124         }
125
126         if (unlikely(!dst->lwtstate->orig_output)) {
127                 pr_warn_once("orig_output not set on dst for prog %s\n",
128                              bpf->out.name);
129                 kfree_skb(skb);
130                 return -EINVAL;
131         }
132
133         return dst->lwtstate->orig_output(net, sk, skb);
134 }
135
136 static int xmit_check_hhlen(struct sk_buff *skb)
137 {
138         int hh_len = skb_dst(skb)->dev->hard_header_len;
139
140         if (skb_headroom(skb) < hh_len) {
141                 int nhead = HH_DATA_ALIGN(hh_len - skb_headroom(skb));
142
143                 if (pskb_expand_head(skb, nhead, 0, GFP_ATOMIC))
144                         return -ENOMEM;
145         }
146
147         return 0;
148 }
149
150 static int bpf_xmit(struct sk_buff *skb)
151 {
152         struct dst_entry *dst = skb_dst(skb);
153         struct bpf_lwt *bpf;
154
155         bpf = bpf_lwt_lwtunnel(dst->lwtstate);
156         if (bpf->xmit.prog) {
157                 int ret;
158
159                 ret = run_lwt_bpf(skb, &bpf->xmit, dst, CAN_REDIRECT);
160                 switch (ret) {
161                 case BPF_OK:
162                         /* If the header was expanded, headroom might be too
163                          * small for L2 header to come, expand as needed.
164                          */
165                         ret = xmit_check_hhlen(skb);
166                         if (unlikely(ret))
167                                 return ret;
168
169                         return LWTUNNEL_XMIT_CONTINUE;
170                 case BPF_REDIRECT:
171                         return LWTUNNEL_XMIT_DONE;
172                 default:
173                         return ret;
174                 }
175         }
176
177         return LWTUNNEL_XMIT_CONTINUE;
178 }
179
180 static void bpf_lwt_prog_destroy(struct bpf_lwt_prog *prog)
181 {
182         if (prog->prog)
183                 bpf_prog_put(prog->prog);
184
185         kfree(prog->name);
186 }
187
188 static void bpf_destroy_state(struct lwtunnel_state *lwt)
189 {
190         struct bpf_lwt *bpf = bpf_lwt_lwtunnel(lwt);
191
192         bpf_lwt_prog_destroy(&bpf->in);
193         bpf_lwt_prog_destroy(&bpf->out);
194         bpf_lwt_prog_destroy(&bpf->xmit);
195 }
196
197 static const struct nla_policy bpf_prog_policy[LWT_BPF_PROG_MAX + 1] = {
198         [LWT_BPF_PROG_FD]   = { .type = NLA_U32, },
199         [LWT_BPF_PROG_NAME] = { .type = NLA_NUL_STRING,
200                                 .len = MAX_PROG_NAME },
201 };
202
203 static int bpf_parse_prog(struct nlattr *attr, struct bpf_lwt_prog *prog,
204                           enum bpf_prog_type type)
205 {
206         struct nlattr *tb[LWT_BPF_PROG_MAX + 1];
207         struct bpf_prog *p;
208         int ret;
209         u32 fd;
210
211         ret = nla_parse_nested(tb, LWT_BPF_PROG_MAX, attr, bpf_prog_policy,
212                                NULL);
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_ATOMIC);
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
233 static 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
240 static int bpf_build_state(struct nlattr *nla,
241                            unsigned int family, const void *cfg,
242                            struct lwtunnel_state **ts,
243                            struct netlink_ext_ack *extack)
244 {
245         struct nlattr *tb[LWT_BPF_MAX + 1];
246         struct lwtunnel_state *newts;
247         struct bpf_lwt *bpf;
248         int ret;
249
250         if (family != AF_INET && family != AF_INET6)
251                 return -EAFNOSUPPORT;
252
253         ret = nla_parse_nested(tb, LWT_BPF_MAX, nla, bpf_nl_policy, extack);
254         if (ret < 0)
255                 return ret;
256
257         if (!tb[LWT_BPF_IN] && !tb[LWT_BPF_OUT] && !tb[LWT_BPF_XMIT])
258                 return -EINVAL;
259
260         newts = lwtunnel_state_alloc(sizeof(*bpf));
261         if (!newts)
262                 return -ENOMEM;
263
264         newts->type = LWTUNNEL_ENCAP_BPF;
265         bpf = bpf_lwt_lwtunnel(newts);
266
267         if (tb[LWT_BPF_IN]) {
268                 newts->flags |= LWTUNNEL_STATE_INPUT_REDIRECT;
269                 ret = bpf_parse_prog(tb[LWT_BPF_IN], &bpf->in,
270                                      BPF_PROG_TYPE_LWT_IN);
271                 if (ret  < 0)
272                         goto errout;
273         }
274
275         if (tb[LWT_BPF_OUT]) {
276                 newts->flags |= LWTUNNEL_STATE_OUTPUT_REDIRECT;
277                 ret = bpf_parse_prog(tb[LWT_BPF_OUT], &bpf->out,
278                                      BPF_PROG_TYPE_LWT_OUT);
279                 if (ret < 0)
280                         goto errout;
281         }
282
283         if (tb[LWT_BPF_XMIT]) {
284                 newts->flags |= LWTUNNEL_STATE_XMIT_REDIRECT;
285                 ret = bpf_parse_prog(tb[LWT_BPF_XMIT], &bpf->xmit,
286                                      BPF_PROG_TYPE_LWT_XMIT);
287                 if (ret < 0)
288                         goto errout;
289         }
290
291         if (tb[LWT_BPF_XMIT_HEADROOM]) {
292                 u32 headroom = nla_get_u32(tb[LWT_BPF_XMIT_HEADROOM]);
293
294                 if (headroom > LWT_BPF_MAX_HEADROOM) {
295                         ret = -ERANGE;
296                         goto errout;
297                 }
298
299                 newts->headroom = headroom;
300         }
301
302         bpf->family = family;
303         *ts = newts;
304
305         return 0;
306
307 errout:
308         bpf_destroy_state(newts);
309         kfree(newts);
310         return ret;
311 }
312
313 static int bpf_fill_lwt_prog(struct sk_buff *skb, int attr,
314                              struct bpf_lwt_prog *prog)
315 {
316         struct nlattr *nest;
317
318         if (!prog->prog)
319                 return 0;
320
321         nest = nla_nest_start(skb, attr);
322         if (!nest)
323                 return -EMSGSIZE;
324
325         if (prog->name &&
326             nla_put_string(skb, LWT_BPF_PROG_NAME, prog->name))
327                 return -EMSGSIZE;
328
329         return nla_nest_end(skb, nest);
330 }
331
332 static int bpf_fill_encap_info(struct sk_buff *skb, struct lwtunnel_state *lwt)
333 {
334         struct bpf_lwt *bpf = bpf_lwt_lwtunnel(lwt);
335
336         if (bpf_fill_lwt_prog(skb, LWT_BPF_IN, &bpf->in) < 0 ||
337             bpf_fill_lwt_prog(skb, LWT_BPF_OUT, &bpf->out) < 0 ||
338             bpf_fill_lwt_prog(skb, LWT_BPF_XMIT, &bpf->xmit) < 0)
339                 return -EMSGSIZE;
340
341         return 0;
342 }
343
344 static int bpf_encap_nlsize(struct lwtunnel_state *lwtstate)
345 {
346         int nest_len = nla_total_size(sizeof(struct nlattr)) +
347                        nla_total_size(MAX_PROG_NAME) + /* LWT_BPF_PROG_NAME */
348                        0;
349
350         return nest_len + /* LWT_BPF_IN */
351                nest_len + /* LWT_BPF_OUT */
352                nest_len + /* LWT_BPF_XMIT */
353                0;
354 }
355
356 static int bpf_lwt_prog_cmp(struct bpf_lwt_prog *a, struct bpf_lwt_prog *b)
357 {
358         /* FIXME:
359          * The LWT state is currently rebuilt for delete requests which
360          * results in a new bpf_prog instance. Comparing names for now.
361          */
362         if (!a->name && !b->name)
363                 return 0;
364
365         if (!a->name || !b->name)
366                 return 1;
367
368         return strcmp(a->name, b->name);
369 }
370
371 static int bpf_encap_cmp(struct lwtunnel_state *a, struct lwtunnel_state *b)
372 {
373         struct bpf_lwt *a_bpf = bpf_lwt_lwtunnel(a);
374         struct bpf_lwt *b_bpf = bpf_lwt_lwtunnel(b);
375
376         return bpf_lwt_prog_cmp(&a_bpf->in, &b_bpf->in) ||
377                bpf_lwt_prog_cmp(&a_bpf->out, &b_bpf->out) ||
378                bpf_lwt_prog_cmp(&a_bpf->xmit, &b_bpf->xmit);
379 }
380
381 static const struct lwtunnel_encap_ops bpf_encap_ops = {
382         .build_state    = bpf_build_state,
383         .destroy_state  = bpf_destroy_state,
384         .input          = bpf_input,
385         .output         = bpf_output,
386         .xmit           = bpf_xmit,
387         .fill_encap     = bpf_fill_encap_info,
388         .get_encap_size = bpf_encap_nlsize,
389         .cmp_encap      = bpf_encap_cmp,
390         .owner          = THIS_MODULE,
391 };
392
393 static int __init bpf_lwt_init(void)
394 {
395         return lwtunnel_encap_add_ops(&bpf_encap_ops, LWTUNNEL_ENCAP_BPF);
396 }
397
398 subsys_initcall(bpf_lwt_init)