1 /*
2 * Linux Socket Filter - Kernel level socket filtering
3 *
4 * Author:
5 * Jay Schulist <jschlst@samba.org>
6 *
7 * Based on the design of:
8 * - The Berkeley Packet Filter
9 *
10 * This program is free software; you can redistribute it and/or
11 * modify it under the terms of the GNU General Public License
12 * as published by the Free Software Foundation; either version
13 * 2 of the License, or (at your option) any later version.
14 *
15 * Andi Kleen - Fix a few bad bugs and races.
16 * Kris Katterjohn - Added many additional checks in sk_chk_filter()
17 */
18
19 #include <linux/module.h>
20 #include <linux/types.h>
21 #include <linux/mm.h>
22 #include <linux/fcntl.h>
23 #include <linux/socket.h>
24 #include <linux/in.h>
25 #include <linux/inet.h>
26 #include <linux/netdevice.h>
27 #include <linux/if_packet.h>
28 #include <net/ip.h>
29 #include <net/protocol.h>
30 #include <linux/skbuff.h>
31 #include <net/sock.h>
32 #include <linux/errno.h>
33 #include <linux/timer.h>
34 #include <asm/system.h>
35 #include <asm/uaccess.h>
36 #include <asm/unaligned.h>
37 #include <linux/filter.h>
38
39 /* No hurry in this branch */
40 static void *__load_pointer(struct sk_buff *skb, int k)
41 {
42 u8 *ptr = NULL;
43
44 if (k >= SKF_NET_OFF)
45 ptr = skb_network_header(skb) + k - SKF_NET_OFF;
46 else if (k >= SKF_LL_OFF)
47 ptr = skb_mac_header(skb) + k - SKF_LL_OFF;
48
49 if (ptr >= skb->head && ptr < skb_tail_pointer(skb))
50 return ptr;
51 return NULL;
52 }
53
54 static inline void *load_pointer(struct sk_buff *skb, int k,
55 unsigned int size, void *buffer)
56 {
57 if (k >= 0)
58 return skb_header_pointer(skb, k, size, buffer);
59 else {
60 if (k >= SKF_AD_OFF)
61 return NULL;
62 return __load_pointer(skb, k);
63 }
64 }
65
66 /**
67 * sk_run_filter - run a filter on a socket
68 * @skb: buffer to run the filter on
69 * @filter: filter to apply
70 * @flen: length of filter
71 *
72 * Decode and apply filter instructions to the skb->data.
73 * Return length to keep, 0 for none. skb is the data we are
74 * filtering, filter is the array of filter instructions, and
75 * len is the number of filter blocks in the array.
76 */
77 unsigned int sk_run_filter(struct sk_buff *skb, struct sock_filter *filter, int flen)
78 {
79 struct sock_filter *fentry; /* We walk down these */
80 void *ptr;
81 u32 A = 0; /* Accumulator */
82 u32 X = 0; /* Index Register */
83 u32 mem[BPF_MEMWORDS]; /* Scratch Memory Store */
84 u32 tmp;
85 int k;
86 int pc;
87
88 /*
89 * Process array of filter instructions.
90 */
91 for (pc = 0; pc < flen; pc++) {
92 fentry = &filter[pc];
93
94 switch (fentry->code) {
95 case BPF_ALU|BPF_ADD|BPF_X:
96 A += X;
97 continue;
98 case BPF_ALU|BPF_ADD|BPF_K:
99 A += fentry->k;
100 continue;
101 case BPF_ALU|BPF_SUB|BPF_X:
102 A -= X;
103 continue;
104 case BPF_ALU|BPF_SUB|BPF_K:
105 A -= fentry->k;
106 continue;
107 case BPF_ALU|BPF_MUL|BPF_X:
108 A *= X;
109 continue;
110 case BPF_ALU|BPF_MUL|BPF_K:
111 A *= fentry->k;
112 continue;
113 case BPF_ALU|BPF_DIV|BPF_X:
114 if (X == 0)
115 return 0;
116 A /= X;
117 continue;
118 case BPF_ALU|BPF_DIV|BPF_K:
119 A /= fentry->k;
120 continue;
121 case BPF_ALU|BPF_AND|BPF_X:
122 A &= X;
123 continue;
124 case BPF_ALU|BPF_AND|BPF_K:
125 A &= fentry->k;
126 continue;
127 case BPF_ALU|BPF_OR|BPF_X:
128 A |= X;
129 continue;
130 case BPF_ALU|BPF_OR|BPF_K:
131 A |= fentry->k;
132 continue;
133 case BPF_ALU|BPF_LSH|BPF_X:
134 A <<= X;
135 continue;
136 case BPF_ALU|BPF_LSH|BPF_K:
137 A <<= fentry->k;
138 continue;
139 case BPF_ALU|BPF_RSH|BPF_X:
140 A >>= X;
141 continue;
142 case BPF_ALU|BPF_RSH|BPF_K:
143 A >>= fentry->k;
144 continue;
145 case BPF_ALU|BPF_NEG:
146 A = -A;
147 continue;
148 case BPF_JMP|BPF_JA:
149 pc += fentry->k;
150 continue;
151 case BPF_JMP|BPF_JGT|BPF_K:
152 pc += (A > fentry->k) ? fentry->jt : fentry->jf;
153 continue;
154 case BPF_JMP|BPF_JGE|BPF_K:
155 pc += (A >= fentry->k) ? fentry->jt : fentry->jf;
156 continue;
157 case BPF_JMP|BPF_JEQ|BPF_K:
158 pc += (A == fentry->k) ? fentry->jt : fentry->jf;
159 continue;
160 case BPF_JMP|BPF_JSET|BPF_K:
161 pc += (A & fentry->k) ? fentry->jt : fentry->jf;
162 continue;
163 case BPF_JMP|BPF_JGT|BPF_X:
164 pc += (A > X) ? fentry->jt : fentry->jf;
165 continue;
166 case BPF_JMP|BPF_JGE|BPF_X:
167 pc += (A >= X) ? fentry->jt : fentry->jf;
168 continue;
169 case BPF_JMP|BPF_JEQ|BPF_X:
170 pc += (A == X) ? fentry->jt : fentry->jf;
171 continue;
172 case BPF_JMP|BPF_JSET|BPF_X:
173 pc += (A & X) ? fentry->jt : fentry->jf;
174 continue;
175 case BPF_LD|BPF_W|BPF_ABS:
176 k = fentry->k;
177 load_w:
178 ptr = load_pointer(skb, k, 4, &tmp);
179 if (ptr != NULL) {
180 A = ntohl(get_unaligned((__be32 *)ptr));
181 continue;
182 }
183 break;
184 case BPF_LD|BPF_H|BPF_ABS:
185 k = fentry->k;
186 load_h:
187 ptr = load_pointer(skb, k, 2, &tmp);
188 if (ptr != NULL) {
189 A = ntohs(get_unaligned((__be16 *)ptr));
190 continue;
191 }
192 break;
193 case BPF_LD|BPF_B|BPF_ABS:
194 k = fentry->k;
195 load_b:
196 ptr = load_pointer(skb, k, 1, &tmp);
197 if (ptr != NULL) {
198 A = *(u8 *)ptr;
199 continue;
200 }
201 break;
202 case BPF_LD|BPF_W|BPF_LEN:
203 A = skb->len;
204 continue;
205 case BPF_LDX|BPF_W|BPF_LEN:
206 X = skb->len;
207 continue;
208 case BPF_LD|BPF_W|BPF_IND:
209 k = X + fentry->k;
210 goto load_w;
211 case BPF_LD|BPF_H|BPF_IND:
212 k = X + fentry->k;
213 goto load_h;
214 case BPF_LD|BPF_B|BPF_IND:
215 k = X + fentry->k;
216 goto load_b;
217 case BPF_LDX|BPF_B|BPF_MSH:
218 ptr = load_pointer(skb, fentry->k, 1, &tmp);
219 if (ptr != NULL) {
220 X = (*(u8 *)ptr & 0xf) << 2;
221 continue;
222 }
223 return 0;
224 case BPF_LD|BPF_IMM:
225 A = fentry->k;
226 continue;
227 case BPF_LDX|BPF_IMM:
228 X = fentry->k;
229 continue;
230 case BPF_LD|BPF_MEM:
231 A = mem[fentry->k];
232 continue;
233 case BPF_LDX|BPF_MEM:
234 X = mem[fentry->k];
235 continue;
236 case BPF_MISC|BPF_TAX:
237 X = A;
238 continue;
239 case BPF_MISC|BPF_TXA:
240 A = X;
241 continue;
242 case BPF_RET|BPF_K:
243 return fentry->k;
244 case BPF_RET|BPF_A:
245 return A;
246 case BPF_ST:
247 mem[fentry->k] = A;
248 continue;
249 case BPF_STX:
250 mem[fentry->k] = X;
251 continue;
252 default:
253 WARN_ON(1);
254 return 0;
255 }
256
257 /*
258 * Handle ancillary data, which are impossible
259 * (or very difficult) to get parsing packet contents.
260 */
261 switch (k-SKF_AD_OFF) {
262 case SKF_AD_PROTOCOL:
263 A = ntohs(skb->protocol);
264 continue;
265 case SKF_AD_PKTTYPE:
266 A = skb->pkt_type;
267 continue;
268 case SKF_AD_IFINDEX:
269 A = skb->dev->ifindex;
270 continue;
271 default:
272 return 0;
273 }
274 }
275
276 return 0;
277 }
278
279 /**
280 * sk_chk_filter - verify socket filter code
281 * @filter: filter to verify
282 * @flen: length of filter
283 *
284 * Check the user's filter code. If we let some ugly
285 * filter code slip through kaboom! The filter must contain
286 * no references or jumps that are out of range, no illegal
287 * instructions, and must end with a RET instruction.
288 *
289 * All jumps are forward as they are not signed.
290 *
291 * Returns 0 if the rule set is legal or -EINVAL if not.
292 */
293 int sk_chk_filter(struct sock_filter *filter, int flen)
294 {
295 struct sock_filter *ftest;
296 int pc;
297
298 if (flen == 0 || flen > BPF_MAXINSNS)
299 return -EINVAL;
300
301 /* check the filter code now */
302 for (pc = 0; pc < flen; pc++) {
303 ftest = &filter[pc];
304
305 /* Only allow valid instructions */
306 switch (ftest->code) {
307 case BPF_ALU|BPF_ADD|BPF_K:
308 case BPF_ALU|BPF_ADD|BPF_X:
309 case BPF_ALU|BPF_SUB|BPF_K:
310 case BPF_ALU|BPF_SUB|BPF_X:
311 case BPF_ALU|BPF_MUL|BPF_K:
312 case BPF_ALU|BPF_MUL|BPF_X:
313 case BPF_ALU|BPF_DIV|BPF_X:
314 case BPF_ALU|BPF_AND|BPF_K:
315 case BPF_ALU|BPF_AND|BPF_X:
316 case BPF_ALU|BPF_OR|BPF_K:
317 case BPF_ALU|BPF_OR|BPF_X:
318 case BPF_ALU|BPF_LSH|BPF_K:
319 case BPF_ALU|BPF_LSH|BPF_X:
320 case BPF_ALU|BPF_RSH|BPF_K:
321 case BPF_ALU|BPF_RSH|BPF_X:
322 case BPF_ALU|BPF_NEG:
323 case BPF_LD|BPF_W|BPF_ABS:
324 case BPF_LD|BPF_H|BPF_ABS:
325 case BPF_LD|BPF_B|BPF_ABS:
326 case BPF_LD|BPF_W|BPF_LEN:
327 case BPF_LD|BPF_W|BPF_IND:
328 case BPF_LD|BPF_H|BPF_IND:
329 case BPF_LD|BPF_B|BPF_IND:
330 case BPF_LD|BPF_IMM:
331 case BPF_LDX|BPF_W|BPF_LEN:
332 case BPF_LDX|BPF_B|BPF_MSH:
333 case BPF_LDX|BPF_IMM:
334 case BPF_MISC|BPF_TAX:
335 case BPF_MISC|BPF_TXA:
336 case BPF_RET|BPF_K:
337 case BPF_RET|BPF_A:
338 break;
339
340 /* Some instructions need special checks */
341
342 case BPF_ALU|BPF_DIV|BPF_K:
343 /* check for division by zero */
344 if (ftest->k == 0)
345 return -EINVAL;
346 break;
347
348 case BPF_LD|BPF_MEM:
349 case BPF_LDX|BPF_MEM:
350 case BPF_ST:
351 case BPF_STX:
352 /* check for invalid memory addresses */
353 if (ftest->k >= BPF_MEMWORDS)
354 return -EINVAL;
355 break;
356
357 case BPF_JMP|BPF_JA:
358 /*
359 * Note, the large ftest->k might cause loops.
360 * Compare this with conditional jumps below,
361 * where offsets are limited. --ANK (981016)
362 */
363 if (ftest->k >= (unsigned)(flen-pc-1))
364 return -EINVAL;
365 break;
366
367 case BPF_JMP|BPF_JEQ|BPF_K:
368 case BPF_JMP|BPF_JEQ|BPF_X:
369 case BPF_JMP|BPF_JGE|BPF_K:
370 case BPF_JMP|BPF_JGE|BPF_X:
371 case BPF_JMP|BPF_JGT|BPF_K:
372 case BPF_JMP|BPF_JGT|BPF_X:
373 case BPF_JMP|BPF_JSET|BPF_K:
374 case BPF_JMP|BPF_JSET|BPF_X:
375 /* for conditionals both must be safe */
376 if (pc + ftest->jt + 1 >= flen ||
377 pc + ftest->jf + 1 >= flen)
378 return -EINVAL;
379 break;
380
381 default:
382 return -EINVAL;
383 }
384 }
385
386 return (BPF_CLASS(filter[flen - 1].code) == BPF_RET) ? 0 : -EINVAL;
387 }
388
389 /**
390 * sk_filter_rcu_release: Release a socket filter by rcu_head
391 * @rcu: rcu_head that contains the sk_filter to free
392 */
393 static void sk_filter_rcu_release(struct rcu_head *rcu)
394 {
395 struct sk_filter *fp = container_of(rcu, struct sk_filter, rcu);
396
397 sk_filter_release(fp);
398 }
399
400 static void sk_filter_delayed_uncharge(struct sock *sk, struct sk_filter *fp)
401 {
402 unsigned int size = sk_filter_len(fp);
403
404 atomic_sub(size, &sk->sk_omem_alloc);
405 call_rcu_bh(&fp->rcu, sk_filter_rcu_release);
406 }
407
408 /**
409 * sk_attach_filter - attach a socket filter
410 * @fprog: the filter program
411 * @sk: the socket to use
412 *
413 * Attach the user's filter code. We first run some sanity checks on
414 * it to make sure it does not explode on us later. If an error
415 * occurs or there is insufficient memory for the filter a negative
416 * errno code is returned. On success the return is zero.
417 */
418 int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk)
419 {
420 struct sk_filter *fp, *old_fp;
421 unsigned int fsize = sizeof(struct sock_filter) * fprog->len;
422 int err;
423
424 /* Make sure new filter is there and in the right amounts. */
425 if (fprog->filter == NULL)
426 return -EINVAL;
427
428 fp = sock_kmalloc(sk, fsize+sizeof(*fp), GFP_KERNEL);
429 if (!fp)
430 return -ENOMEM;
431 if (copy_from_user(fp->insns, fprog->filter, fsize)) {
432 sock_kfree_s(sk, fp, fsize+sizeof(*fp));
433 return -EFAULT;
434 }
435
436 atomic_set(&fp->refcnt, 1);
437 fp->len = fprog->len;
438
439 err = sk_chk_filter(fp->insns, fp->len);
440 if (err) {
441 sk_filter_uncharge(sk, fp);
442 return err;
443 }
444
445 rcu_read_lock_bh();
446 old_fp = rcu_dereference(sk->sk_filter);
447 rcu_assign_pointer(sk->sk_filter, fp);
448 rcu_read_unlock_bh();
449
450 if (old_fp)
451 sk_filter_delayed_uncharge(sk, old_fp);
452 return 0;
453 }
454
455 int sk_detach_filter(struct sock *sk)
456 {
457 int ret = -ENOENT;
458 struct sk_filter *filter;
459
460 rcu_read_lock_bh();
461 filter = rcu_dereference(sk->sk_filter);
462 if (filter) {
463 rcu_assign_pointer(sk->sk_filter, NULL);
464 sk_filter_delayed_uncharge(sk, filter);
465 ret = 0;
466 }
467 rcu_read_unlock_bh();
468 return ret;
469 }
470
471 EXPORT_SYMBOL(sk_chk_filter);
472 EXPORT_SYMBOL(sk_run_filter);
473
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