lzo1x_decompress_safe.cpp

/*
 *  LZO1X Decompressor from LZO
 *
 *  Copyright (C) 1996-2012 Markus F.X.J. Oberhumer <markus@oberhumer.com>
 *
 *  The full LZO package can be found at:
 *  http://www.oberhumer.com/opensource/lzo/
 *
 *  Changed for Linux kernel use by:
 *  Nitin Gupta <nitingupta910@gmail.com>
 *  Richard Purdie <rpurdie@openedhand.com>
 */

#include "unaligned.h"
#include "lzo.h"
#include "lzodefs.h"

#define HAVE_IP(x)      ((size_t)(ip_end - ip) >= (size_t)(x))
#define HAVE_OP(x)      ((size_t)(op_end - op) >= (size_t)(x))
#define NEED_IP(x)      if (!HAVE_IP(x)) goto input_overrun
#define NEED_OP(x)      if (!HAVE_OP(x)) goto output_overrun
#define TEST_LB(m_pos)  if ((m_pos) < out) goto lookbehind_overrun

/* This MAX_255_COUNT is the maximum number of times we can add 255 to a base
 * count without overflowing an integer. The multiply will overflow when
 * multiplying 255 by more than MAXINT/255. The sum will overflow earlier
 * depending on the base count. Since the base count is taken from a u8
 * and a few bits, it is safe to assume that it will always be lower than
 * or equal to 2*255, thus we can always prevent any overflow by accepting
 * two less 255 steps. See Documentation/lzo.txt for more information.
 */
#define MAX_255_COUNT      ((((size_t)~0) / 255) - 2)

int lzo1x_decompress_safe(const unsigned char *in, size_t in_len,
			  unsigned char *out, size_t *out_len)
{
	unsigned char *op;
	const unsigned char *ip;
	size_t t, next;
	size_t state = 0;
	const unsigned char *m_pos;
	const unsigned char * const ip_end = in + in_len;
	unsigned char * const op_end = out + *out_len;

	unsigned char bitstream_version;

	op = out;
	ip = in;

	if (unlikely(in_len < 3))
		goto input_overrun;

	if (likely(*ip == 17)) {
		bitstream_version = ip[1];
		ip += 2;
		if (unlikely(in_len < 5))
			goto input_overrun;
	} else {
		bitstream_version = 0;
	}

	if (*ip > 17) {
		t = *ip++ - 17;
		if (t < 4) {
			next = t;
			goto match_next;
		}
		goto copy_literal_run;
	}

	for (;;) {
		t = *ip++;
		if (t < 16) {
			if (likely(state == 0)) {
				if (unlikely(t == 0)) {
					size_t offset;
					const unsigned char *ip_last = ip;

					while (unlikely(*ip == 0)) {
						ip++;
						NEED_IP(1);
					}
					offset = ip - ip_last;
					if (unlikely(offset > MAX_255_COUNT))
						return LZO_E_ERROR;

					offset = (offset << 8) - offset;
					t += offset + 15 + *ip++;
				}
				t += 3;
copy_literal_run:
#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
				if (likely(HAVE_IP(t + 15) && HAVE_OP(t + 15))) {
					const unsigned char *ie = ip + t;
					unsigned char *oe = op + t;
					do {
						COPY8(op, ip);
						op += 8;
						ip += 8;
						COPY8(op, ip);
						op += 8;
						ip += 8;
					} while (ip < ie);
					ip = ie;
					op = oe;
				} else
#endif
				{
					NEED_OP(t);
					NEED_IP(t + 3);
					do {
						*op++ = *ip++;
					} while (--t > 0);
				}
				state = 4;
				continue;
			} else if (state != 4) {
				next = t & 3;
				m_pos = op - 1;
				m_pos -= t >> 2;
				m_pos -= *ip++ << 2;
				TEST_LB(m_pos);
				NEED_OP(2);
				op[0] = m_pos[0];
				op[1] = m_pos[1];
				op += 2;
				goto match_next;
			} else {
				next = t & 3;
				m_pos = op - (1 + M2_MAX_OFFSET);
				m_pos -= t >> 2;
				m_pos -= *ip++ << 2;
				t = 3;
			}
		} else if (t >= 64) {
			next = t & 3;
			m_pos = op - 1;
			m_pos -= (t >> 2) & 7;
			m_pos -= *ip++ << 3;
			t = (t >> 5) - 1 + (3 - 1);
		} else if (t >= 32) {
			t = (t & 31) + (3 - 1);
			if (unlikely(t == 2)) {
				size_t offset;
				const unsigned char *ip_last = ip;

				while (unlikely(*ip == 0)) {
					ip++;
					NEED_IP(1);
				}
				offset = ip - ip_last;
				if (unlikely(offset > MAX_255_COUNT))
					return LZO_E_ERROR;

				offset = (offset << 8) - offset;
				t += offset + 31 + *ip++;
				NEED_IP(2);
			}
			m_pos = op - 1;
			next = get_unaligned_le16(ip);
			ip += 2;
			m_pos -= next >> 2;
			next &= 3;
		} else {
			NEED_IP(2);
			next = get_unaligned_le16(ip);
			if (((next & 0xfffc) == 0xfffc) &&
			    ((t & 0xf8) == 0x18) &&
			    likely(bitstream_version)) {
				NEED_IP(3);
				t &= 7;
				t |= ip[2] << 3;
				t += MIN_ZERO_RUN_LENGTH;
				NEED_OP(t);
				memset(op, 0, t);
				op += t;
				next &= 3;
				ip += 3;
				goto match_next;
			} else {
				m_pos = op;
				m_pos -= (t & 8) << 11;
				t = (t & 7) + (3 - 1);
				if (unlikely(t == 2)) {
					size_t offset;
					const unsigned char *ip_last = ip;

					while (unlikely(*ip == 0)) {
						ip++;
						NEED_IP(1);
					}
					offset = ip - ip_last;
					if (unlikely(offset > MAX_255_COUNT))
						return LZO_E_ERROR;

					offset = (offset << 8) - offset;
					t += offset + 7 + *ip++;
					NEED_IP(2);
					next = get_unaligned_le16(ip);
				}
				ip += 2;
				m_pos -= next >> 2;
				next &= 3;
				if (m_pos == op)
					goto eof_found;
				m_pos -= 0x4000;
			}
		}
		TEST_LB(m_pos);
#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
		if (op - m_pos >= 8) {
			unsigned char *oe = op + t;
			if (likely(HAVE_OP(t + 15))) {
				do {
					COPY8(op, m_pos);
					op += 8;
					m_pos += 8;
					COPY8(op, m_pos);
					op += 8;
					m_pos += 8;
				} while (op < oe);
				op = oe;
				if (HAVE_IP(6)) {
					state = next;
					COPY4(op, ip);
					op += next;
					ip += next;
					continue;
				}
			} else {
				NEED_OP(t);
				do {
					*op++ = *m_pos++;
				} while (op < oe);
			}
		} else
#endif
		{
			unsigned char *oe = op + t;
			NEED_OP(t);
			op[0] = m_pos[0];
			op[1] = m_pos[1];
			op += 2;
			m_pos += 2;
			do {
				*op++ = *m_pos++;
			} while (op < oe);
		}
match_next:
		state = next;
		t = next;
#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
		if (likely(HAVE_IP(6) && HAVE_OP(4))) {
			COPY4(op, ip);
			op += t;
			ip += t;
		} else
#endif
		{
			NEED_IP(t + 3);
			NEED_OP(t);
			while (t > 0) {
				*op++ = *ip++;
				t--;
			}
		}
	}

eof_found:
	*out_len = op - out;
	return (t != 3       ? LZO_E_ERROR :
		ip == ip_end ? LZO_E_OK :
		ip <  ip_end ? LZO_E_INPUT_NOT_CONSUMED : LZO_E_INPUT_OVERRUN);

input_overrun:
	*out_len = op - out;
	return LZO_E_INPUT_OVERRUN;

output_overrun:
	*out_len = op - out;
	return LZO_E_OUTPUT_OVERRUN;

lookbehind_overrun:
	*out_len = op - out;
	return LZO_E_LOOKBEHIND_OVERRUN;
}