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Linux/net/core/lwt_bpf.c

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  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         rcu_read_lock();
 54         bpf_compute_data_pointers(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 
 91 static 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 
114 static 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 
137 static 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 
151 static 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 
181 static 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 
189 static 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 
198 static 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 
204 static 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                                NULL);
214         if (ret < 0)
215                 return ret;
216 
217         if (!tb[LWT_BPF_PROG_FD] || !tb[LWT_BPF_PROG_NAME])
218                 return -EINVAL;
219 
220         prog->name = nla_memdup(tb[LWT_BPF_PROG_NAME], GFP_KERNEL);
221         if (!prog->name)
222                 return -ENOMEM;
223 
224         fd = nla_get_u32(tb[LWT_BPF_PROG_FD]);
225         p = bpf_prog_get_type(fd, type);
226         if (IS_ERR(p))
227                 return PTR_ERR(p);
228 
229         prog->prog = p;
230 
231         return 0;
232 }
233 
234 static const struct nla_policy bpf_nl_policy[LWT_BPF_MAX + 1] = {
235         [LWT_BPF_IN]            = { .type = NLA_NESTED, },
236         [LWT_BPF_OUT]           = { .type = NLA_NESTED, },
237         [LWT_BPF_XMIT]          = { .type = NLA_NESTED, },
238         [LWT_BPF_XMIT_HEADROOM] = { .type = NLA_U32 },
239 };
240 
241 static int bpf_build_state(struct nlattr *nla,
242                            unsigned int family, const void *cfg,
243                            struct lwtunnel_state **ts,
244                            struct netlink_ext_ack *extack)
245 {
246         struct nlattr *tb[LWT_BPF_MAX + 1];
247         struct lwtunnel_state *newts;
248         struct bpf_lwt *bpf;
249         int ret;
250 
251         if (family != AF_INET && family != AF_INET6)
252                 return -EAFNOSUPPORT;
253 
254         ret = nla_parse_nested(tb, LWT_BPF_MAX, nla, bpf_nl_policy, extack);
255         if (ret < 0)
256                 return ret;
257 
258         if (!tb[LWT_BPF_IN] && !tb[LWT_BPF_OUT] && !tb[LWT_BPF_XMIT])
259                 return -EINVAL;
260 
261         newts = lwtunnel_state_alloc(sizeof(*bpf));
262         if (!newts)
263                 return -ENOMEM;
264 
265         newts->type = LWTUNNEL_ENCAP_BPF;
266         bpf = bpf_lwt_lwtunnel(newts);
267 
268         if (tb[LWT_BPF_IN]) {
269                 newts->flags |= LWTUNNEL_STATE_INPUT_REDIRECT;
270                 ret = bpf_parse_prog(tb[LWT_BPF_IN], &bpf->in,
271                                      BPF_PROG_TYPE_LWT_IN);
272                 if (ret  < 0)
273                         goto errout;
274         }
275 
276         if (tb[LWT_BPF_OUT]) {
277                 newts->flags |= LWTUNNEL_STATE_OUTPUT_REDIRECT;
278                 ret = bpf_parse_prog(tb[LWT_BPF_OUT], &bpf->out,
279                                      BPF_PROG_TYPE_LWT_OUT);
280                 if (ret < 0)
281                         goto errout;
282         }
283 
284         if (tb[LWT_BPF_XMIT]) {
285                 newts->flags |= LWTUNNEL_STATE_XMIT_REDIRECT;
286                 ret = bpf_parse_prog(tb[LWT_BPF_XMIT], &bpf->xmit,
287                                      BPF_PROG_TYPE_LWT_XMIT);
288                 if (ret < 0)
289                         goto errout;
290         }
291 
292         if (tb[LWT_BPF_XMIT_HEADROOM]) {
293                 u32 headroom = nla_get_u32(tb[LWT_BPF_XMIT_HEADROOM]);
294 
295                 if (headroom > LWT_BPF_MAX_HEADROOM) {
296                         ret = -ERANGE;
297                         goto errout;
298                 }
299 
300                 newts->headroom = headroom;
301         }
302 
303         bpf->family = family;
304         *ts = newts;
305 
306         return 0;
307 
308 errout:
309         bpf_destroy_state(newts);
310         kfree(newts);
311         return ret;
312 }
313 
314 static int bpf_fill_lwt_prog(struct sk_buff *skb, int attr,
315                              struct bpf_lwt_prog *prog)
316 {
317         struct nlattr *nest;
318 
319         if (!prog->prog)
320                 return 0;
321 
322         nest = nla_nest_start(skb, attr);
323         if (!nest)
324                 return -EMSGSIZE;
325 
326         if (prog->name &&
327             nla_put_string(skb, LWT_BPF_PROG_NAME, prog->name))
328                 return -EMSGSIZE;
329 
330         return nla_nest_end(skb, nest);
331 }
332 
333 static int bpf_fill_encap_info(struct sk_buff *skb, struct lwtunnel_state *lwt)
334 {
335         struct bpf_lwt *bpf = bpf_lwt_lwtunnel(lwt);
336 
337         if (bpf_fill_lwt_prog(skb, LWT_BPF_IN, &bpf->in) < 0 ||
338             bpf_fill_lwt_prog(skb, LWT_BPF_OUT, &bpf->out) < 0 ||
339             bpf_fill_lwt_prog(skb, LWT_BPF_XMIT, &bpf->xmit) < 0)
340                 return -EMSGSIZE;
341 
342         return 0;
343 }
344 
345 static int bpf_encap_nlsize(struct lwtunnel_state *lwtstate)
346 {
347         int nest_len = nla_total_size(sizeof(struct nlattr)) +
348                        nla_total_size(MAX_PROG_NAME) + /* LWT_BPF_PROG_NAME */
349                        0;
350 
351         return nest_len + /* LWT_BPF_IN */
352                nest_len + /* LWT_BPF_OUT */
353                nest_len + /* LWT_BPF_XMIT */
354                0;
355 }
356 
357 static int bpf_lwt_prog_cmp(struct bpf_lwt_prog *a, struct bpf_lwt_prog *b)
358 {
359         /* FIXME:
360          * The LWT state is currently rebuilt for delete requests which
361          * results in a new bpf_prog instance. Comparing names for now.
362          */
363         if (!a->name && !b->name)
364                 return 0;
365 
366         if (!a->name || !b->name)
367                 return 1;
368 
369         return strcmp(a->name, b->name);
370 }
371 
372 static int bpf_encap_cmp(struct lwtunnel_state *a, struct lwtunnel_state *b)
373 {
374         struct bpf_lwt *a_bpf = bpf_lwt_lwtunnel(a);
375         struct bpf_lwt *b_bpf = bpf_lwt_lwtunnel(b);
376 
377         return bpf_lwt_prog_cmp(&a_bpf->in, &b_bpf->in) ||
378                bpf_lwt_prog_cmp(&a_bpf->out, &b_bpf->out) ||
379                bpf_lwt_prog_cmp(&a_bpf->xmit, &b_bpf->xmit);
380 }
381 
382 static const struct lwtunnel_encap_ops bpf_encap_ops = {
383         .build_state    = bpf_build_state,
384         .destroy_state  = bpf_destroy_state,
385         .input          = bpf_input,
386         .output         = bpf_output,
387         .xmit           = bpf_xmit,
388         .fill_encap     = bpf_fill_encap_info,
389         .get_encap_size = bpf_encap_nlsize,
390         .cmp_encap      = bpf_encap_cmp,
391         .owner          = THIS_MODULE,
392 };
393 
394 static int __init bpf_lwt_init(void)
395 {
396         return lwtunnel_encap_add_ops(&bpf_encap_ops, LWTUNNEL_ENCAP_BPF);
397 }
398 
399 subsys_initcall(bpf_lwt_init)
400 

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