bpf_filter.c revision 356341 
1/*-
2 * Copyright (c) 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997
3 *	The Regents of the University of California.  All rights reserved.
4 *
5 * This code is derived from the Stanford/CMU enet packet filter,
6 * (net/enet.c) distributed as part of 4.3BSD, and code contributed
7 * to Berkeley by Steven McCanne and Van Jacobson both of Lawrence
8 * Berkeley Laboratory.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 *    notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 *    notice, this list of conditions and the following disclaimer in the
17 *    documentation and/or other materials provided with the distribution.
18 * 3. All advertising materials mentioning features or use of this software
19 *    must display the following acknowledgement:
20 *	This product includes software developed by the University of
21 *	California, Berkeley and its contributors.
22 * 4. Neither the name of the University nor the names of its contributors
23 *    may be used to endorse or promote products derived from this software
24 *    without specific prior written permission.
25 *
26 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
27 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
28 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
29 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
30 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
31 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
32 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
33 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
34 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
35 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
36 * SUCH DAMAGE.
37 *
38 *	@(#)bpf.c	7.5 (Berkeley) 7/15/91
39 */
40
41#ifdef HAVE_CONFIG_H
42#include <config.h>
43#endif
44
45#include <pcap/pcap-inttypes.h>
46#include "pcap-types.h"
47
48#ifndef _WIN32
49#include <sys/param.h>
50#include <sys/types.h>
51#include <sys/time.h>
52#endif /* _WIN32 */
53
54#include <pcap-int.h>
55
56#include <stdlib.h>
57
58#define int32 bpf_int32
59#define u_int32 bpf_u_int32
60
61#ifndef LBL_ALIGN
62/*
63 * XXX - IA-64?  If not, this probably won't work on Win64 IA-64
64 * systems, unless LBL_ALIGN is defined elsewhere for them.
65 * XXX - SuperH?  If not, this probably won't work on WinCE SuperH
66 * systems, unless LBL_ALIGN is defined elsewhere for them.
67 */
68#if defined(sparc) || defined(__sparc__) || defined(mips) || \
69    defined(ibm032) || defined(__alpha) || defined(__hpux) || \
70    defined(__arm__)
71#define LBL_ALIGN
72#endif
73#endif
74
75#ifndef LBL_ALIGN
76#ifndef _WIN32
77#include <netinet/in.h>
78#endif
79
80#define EXTRACT_SHORT(p)	((u_short)ntohs(*(u_short *)p))
81#define EXTRACT_LONG(p)		(ntohl(*(u_int32 *)p))
82#else
83#define EXTRACT_SHORT(p)\
84	((u_short)\
85		((u_short)*((u_char *)p+0)<<8|\
86		 (u_short)*((u_char *)p+1)<<0))
87#define EXTRACT_LONG(p)\
88		((u_int32)*((u_char *)p+0)<<24|\
89		 (u_int32)*((u_char *)p+1)<<16|\
90		 (u_int32)*((u_char *)p+2)<<8|\
91		 (u_int32)*((u_char *)p+3)<<0)
92#endif
93
94#ifdef __linux__
95#include <linux/types.h>
96#include <linux/if_packet.h>
97#include <linux/filter.h>
98#endif
99
100enum {
101        BPF_S_ANC_NONE,
102        BPF_S_ANC_VLAN_TAG,
103        BPF_S_ANC_VLAN_TAG_PRESENT,
104};
105
106/*
107 * Execute the filter program starting at pc on the packet p
108 * wirelen is the length of the original packet
109 * buflen is the amount of data present
110 * aux_data is auxiliary data, currently used only when interpreting
111 * filters intended for the Linux kernel in cases where the kernel
112 * rejects the filter; it contains VLAN tag information
113 * For the kernel, p is assumed to be a pointer to an mbuf if buflen is 0,
114 * in all other cases, p is a pointer to a buffer and buflen is its size.
115 *
116 * Thanks to Ani Sinha <ani@arista.com> for providing initial implementation
117 */
118u_int
119bpf_filter_with_aux_data(const struct bpf_insn *pc, const u_char *p,
120    u_int wirelen, u_int buflen, const struct bpf_aux_data *aux_data)
121{
122	register u_int32 A, X;
123	register bpf_u_int32 k;
124	u_int32 mem[BPF_MEMWORDS];
125
126	if (pc == 0)
127		/*
128		 * No filter means accept all.
129		 */
130		return (u_int)-1;
131	A = 0;
132	X = 0;
133	--pc;
134	for (;;) {
135		++pc;
136		switch (pc->code) {
137
138		default:
139			abort();
140		case BPF_RET|BPF_K:
141			return (u_int)pc->k;
142
143		case BPF_RET|BPF_A:
144			return (u_int)A;
145
146		case BPF_LD|BPF_W|BPF_ABS:
147			k = pc->k;
148			if (k > buflen || sizeof(int32_t) > buflen - k) {
149				return 0;
150			}
151			A = EXTRACT_LONG(&p[k]);
152			continue;
153
154		case BPF_LD|BPF_H|BPF_ABS:
155			k = pc->k;
156			if (k > buflen || sizeof(int16_t) > buflen - k) {
157				return 0;
158			}
159			A = EXTRACT_SHORT(&p[k]);
160			continue;
161
162		case BPF_LD|BPF_B|BPF_ABS:
163			switch (pc->k) {
164
165#if defined(SKF_AD_VLAN_TAG_PRESENT)
166			case SKF_AD_OFF + SKF_AD_VLAN_TAG:
167				if (!aux_data)
168					return 0;
169				A = aux_data->vlan_tag;
170				break;
171
172			case SKF_AD_OFF + SKF_AD_VLAN_TAG_PRESENT:
173				if (!aux_data)
174					return 0;
175				A = aux_data->vlan_tag_present;
176				break;
177#endif
178			default:
179				k = pc->k;
180				if (k >= buflen) {
181					return 0;
182				}
183				A = p[k];
184				break;
185			}
186			continue;
187
188		case BPF_LD|BPF_W|BPF_LEN:
189			A = wirelen;
190			continue;
191
192		case BPF_LDX|BPF_W|BPF_LEN:
193			X = wirelen;
194			continue;
195
196		case BPF_LD|BPF_W|BPF_IND:
197			k = X + pc->k;
198			if (pc->k > buflen || X > buflen - pc->k ||
199			    sizeof(int32_t) > buflen - k) {
200				return 0;
201			}
202			A = EXTRACT_LONG(&p[k]);
203			continue;
204
205		case BPF_LD|BPF_H|BPF_IND:
206			k = X + pc->k;
207			if (X > buflen || pc->k > buflen - X ||
208			    sizeof(int16_t) > buflen - k) {
209				return 0;
210			}
211			A = EXTRACT_SHORT(&p[k]);
212			continue;
213
214		case BPF_LD|BPF_B|BPF_IND:
215			k = X + pc->k;
216			if (pc->k >= buflen || X >= buflen - pc->k) {
217				return 0;
218			}
219			A = p[k];
220			continue;
221
222		case BPF_LDX|BPF_MSH|BPF_B:
223			k = pc->k;
224			if (k >= buflen) {
225				return 0;
226			}
227			X = (p[pc->k] & 0xf) << 2;
228			continue;
229
230		case BPF_LD|BPF_IMM:
231			A = pc->k;
232			continue;
233
234		case BPF_LDX|BPF_IMM:
235			X = pc->k;
236			continue;
237
238		case BPF_LD|BPF_MEM:
239			A = mem[pc->k];
240			continue;
241
242		case BPF_LDX|BPF_MEM:
243			X = mem[pc->k];
244			continue;
245
246		case BPF_ST:
247			mem[pc->k] = A;
248			continue;
249
250		case BPF_STX:
251			mem[pc->k] = X;
252			continue;
253
254		case BPF_JMP|BPF_JA:
255			/*
256			 * XXX - we currently implement "ip6 protochain"
257			 * with backward jumps, so sign-extend pc->k.
258			 */
259			pc += (bpf_int32)pc->k;
260			continue;
261
262		case BPF_JMP|BPF_JGT|BPF_K:
263			pc += (A > pc->k) ? pc->jt : pc->jf;
264			continue;
265
266		case BPF_JMP|BPF_JGE|BPF_K:
267			pc += (A >= pc->k) ? pc->jt : pc->jf;
268			continue;
269
270		case BPF_JMP|BPF_JEQ|BPF_K:
271			pc += (A == pc->k) ? pc->jt : pc->jf;
272			continue;
273
274		case BPF_JMP|BPF_JSET|BPF_K:
275			pc += (A & pc->k) ? pc->jt : pc->jf;
276			continue;
277
278		case BPF_JMP|BPF_JGT|BPF_X:
279			pc += (A > X) ? pc->jt : pc->jf;
280			continue;
281
282		case BPF_JMP|BPF_JGE|BPF_X:
283			pc += (A >= X) ? pc->jt : pc->jf;
284			continue;
285
286		case BPF_JMP|BPF_JEQ|BPF_X:
287			pc += (A == X) ? pc->jt : pc->jf;
288			continue;
289
290		case BPF_JMP|BPF_JSET|BPF_X:
291			pc += (A & X) ? pc->jt : pc->jf;
292			continue;
293
294		case BPF_ALU|BPF_ADD|BPF_X:
295			A += X;
296			continue;
297
298		case BPF_ALU|BPF_SUB|BPF_X:
299			A -= X;
300			continue;
301
302		case BPF_ALU|BPF_MUL|BPF_X:
303			A *= X;
304			continue;
305
306		case BPF_ALU|BPF_DIV|BPF_X:
307			if (X == 0)
308				return 0;
309			A /= X;
310			continue;
311
312		case BPF_ALU|BPF_MOD|BPF_X:
313			if (X == 0)
314				return 0;
315			A %= X;
316			continue;
317
318		case BPF_ALU|BPF_AND|BPF_X:
319			A &= X;
320			continue;
321
322		case BPF_ALU|BPF_OR|BPF_X:
323			A |= X;
324			continue;
325
326		case BPF_ALU|BPF_XOR|BPF_X:
327			A ^= X;
328			continue;
329
330		case BPF_ALU|BPF_LSH|BPF_X:
331			if (X < 32)
332				A <<= X;
333			else
334				A = 0;
335			continue;
336
337		case BPF_ALU|BPF_RSH|BPF_X:
338			if (X < 32)
339				A >>= X;
340			else
341				A = 0;
342			continue;
343
344		case BPF_ALU|BPF_ADD|BPF_K:
345			A += pc->k;
346			continue;
347
348		case BPF_ALU|BPF_SUB|BPF_K:
349			A -= pc->k;
350			continue;
351
352		case BPF_ALU|BPF_MUL|BPF_K:
353			A *= pc->k;
354			continue;
355
356		case BPF_ALU|BPF_DIV|BPF_K:
357			A /= pc->k;
358			continue;
359
360		case BPF_ALU|BPF_MOD|BPF_K:
361			A %= pc->k;
362			continue;
363
364		case BPF_ALU|BPF_AND|BPF_K:
365			A &= pc->k;
366			continue;
367
368		case BPF_ALU|BPF_OR|BPF_K:
369			A |= pc->k;
370			continue;
371
372		case BPF_ALU|BPF_XOR|BPF_K:
373			A ^= pc->k;
374			continue;
375
376		case BPF_ALU|BPF_LSH|BPF_K:
377			A <<= pc->k;
378			continue;
379
380		case BPF_ALU|BPF_RSH|BPF_K:
381			A >>= pc->k;
382			continue;
383
384		case BPF_ALU|BPF_NEG:
385			/*
386			 * Most BPF arithmetic is unsigned, but negation
387			 * can't be unsigned; respecify it as subtracting
388			 * the accumulator from 0U, so that 1) we don't
389			 * get compiler warnings about negating an unsigned
390			 * value and 2) don't get UBSan warnings about
391			 * the result of negating 0x80000000 being undefined.
392			 */
393			A = (0U - A);
394			continue;
395
396		case BPF_MISC|BPF_TAX:
397			X = A;
398			continue;
399
400		case BPF_MISC|BPF_TXA:
401			A = X;
402			continue;
403		}
404	}
405}
406
407u_int
408bpf_filter(const struct bpf_insn *pc, const u_char *p, u_int wirelen,
409    u_int buflen)
410{
411	return bpf_filter_with_aux_data(pc, p, wirelen, buflen, NULL);
412}
413
414
415/*
416 * Return true if the 'fcode' is a valid filter program.
417 * The constraints are that each jump be forward and to a valid
418 * code, that memory accesses are within valid ranges (to the
419 * extent that this can be checked statically; loads of packet
420 * data have to be, and are, also checked at run time), and that
421 * the code terminates with either an accept or reject.
422 *
423 * The kernel needs to be able to verify an application's filter code.
424 * Otherwise, a bogus program could easily crash the system.
425 */
426int
427bpf_validate(const struct bpf_insn *f, int len)
428{
429	u_int i, from;
430	const struct bpf_insn *p;
431
432	if (len < 1)
433		return 0;
434
435	for (i = 0; i < (u_int)len; ++i) {
436		p = &f[i];
437		switch (BPF_CLASS(p->code)) {
438		/*
439		 * Check that memory operations use valid addresses.
440		 */
441		case BPF_LD:
442		case BPF_LDX:
443			switch (BPF_MODE(p->code)) {
444			case BPF_IMM:
445				break;
446			case BPF_ABS:
447			case BPF_IND:
448			case BPF_MSH:
449				/*
450				 * There's no maximum packet data size
451				 * in userland.  The runtime packet length
452				 * check suffices.
453				 */
454				break;
455			case BPF_MEM:
456				if (p->k >= BPF_MEMWORDS)
457					return 0;
458				break;
459			case BPF_LEN:
460				break;
461			default:
462				return 0;
463			}
464			break;
465		case BPF_ST:
466		case BPF_STX:
467			if (p->k >= BPF_MEMWORDS)
468				return 0;
469			break;
470		case BPF_ALU:
471			switch (BPF_OP(p->code)) {
472			case BPF_ADD:
473			case BPF_SUB:
474			case BPF_MUL:
475			case BPF_OR:
476			case BPF_AND:
477			case BPF_XOR:
478			case BPF_LSH:
479			case BPF_RSH:
480			case BPF_NEG:
481				break;
482			case BPF_DIV:
483			case BPF_MOD:
484				/*
485				 * Check for constant division or modulus
486				 * by 0.
487				 */
488				if (BPF_SRC(p->code) == BPF_K && p->k == 0)
489					return 0;
490				break;
491			default:
492				return 0;
493			}
494			break;
495		case BPF_JMP:
496			/*
497			 * Check that jumps are within the code block,
498			 * and that unconditional branches don't go
499			 * backwards as a result of an overflow.
500			 * Unconditional branches have a 32-bit offset,
501			 * so they could overflow; we check to make
502			 * sure they don't.  Conditional branches have
503			 * an 8-bit offset, and the from address is <=
504			 * BPF_MAXINSNS, and we assume that BPF_MAXINSNS
505			 * is sufficiently small that adding 255 to it
506			 * won't overflow.
507			 *
508			 * We know that len is <= BPF_MAXINSNS, and we
509			 * assume that BPF_MAXINSNS is < the maximum size
510			 * of a u_int, so that i + 1 doesn't overflow.
511			 *
512			 * For userland, we don't know that the from
513			 * or len are <= BPF_MAXINSNS, but we know that
514			 * from <= len, and, except on a 64-bit system,
515			 * it's unlikely that len, if it truly reflects
516			 * the size of the program we've been handed,
517			 * will be anywhere near the maximum size of
518			 * a u_int.  We also don't check for backward
519			 * branches, as we currently support them in
520			 * userland for the protochain operation.
521			 */
522			from = i + 1;
523			switch (BPF_OP(p->code)) {
524			case BPF_JA:
525				if (from + p->k >= (u_int)len)
526					return 0;
527				break;
528			case BPF_JEQ:
529			case BPF_JGT:
530			case BPF_JGE:
531			case BPF_JSET:
532				if (from + p->jt >= (u_int)len || from + p->jf >= (u_int)len)
533					return 0;
534				break;
535			default:
536				return 0;
537			}
538			break;
539		case BPF_RET:
540			break;
541		case BPF_MISC:
542			break;
543		default:
544			return 0;
545		}
546	}
547	return BPF_CLASS(f[len - 1].code) == BPF_RET;
548}
549