158 lines
3.7 KiB
C
158 lines
3.7 KiB
C
/*
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* Decompression code for Plain LZ77. This encoding is used by
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* Microsoft in various file formats and protocols including SMB3.
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*
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* See MS-XCA.
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*
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* Copyright (C) 2019 Aurélien Aptel
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*
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* SPDX-License-Identifier: GPL-2.0-or-later
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*/
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#include <glib.h>
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#include <epan/exceptions.h>
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#include <epan/tvbuff.h>
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#include <epan/wmem_scopes.h>
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#define MAX_INPUT_SIZE (16*1024*1024) /* 16MB */
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static gboolean do_uncompress(tvbuff_t *tvb, int offset, int in_size,
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wmem_array_t *obuf)
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{
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guint buf_flags = 0, buf_flag_count = 0;
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int in_off = 0;
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int last_length_half_byte = 0;
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guint match_bytes, match_len, match_off;
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guint i;
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if (!tvb)
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return FALSE;
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if (!in_size || in_size > MAX_INPUT_SIZE)
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return FALSE;
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while (1) {
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if (buf_flag_count == 0) {
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buf_flags = tvb_get_letohl(tvb, offset+in_off);
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in_off += 4;
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buf_flag_count = 32;
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}
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buf_flag_count--;
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if ((buf_flags & (1u << buf_flag_count)) == 0) {
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guint8 v = tvb_get_guint8(tvb, offset+in_off);
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wmem_array_append_one(obuf, v);
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in_off++;
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} else {
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if (in_off == in_size)
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return TRUE;
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match_bytes = tvb_get_letohs(tvb, offset+in_off);
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in_off += 2;
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match_len = match_bytes % 8;
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match_off = (match_bytes/8) + 1;
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if (match_len == 7) {
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if (last_length_half_byte == 0) {
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match_len = tvb_get_guint8(tvb, offset+in_off);
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match_len = match_len % 16;
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last_length_half_byte = in_off;
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in_off++;
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} else {
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match_len = tvb_get_guint8(tvb, offset+last_length_half_byte);
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match_len = match_len / 16;
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last_length_half_byte = 0;
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}
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if (match_len == 15) {
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match_len = tvb_get_guint8(tvb, offset+in_off);
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in_off++;
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if (match_len == 255) {
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match_len = tvb_get_letohs(tvb, offset+in_off);
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in_off += 2;
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if (match_len == 0) {
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/* This case isn't documented */
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match_len = tvb_get_letohs(tvb, offset+in_off);
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in_off += 4;
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}
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if (match_len < 15+7)
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return FALSE;
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match_len -= (15 + 7);
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}
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match_len += 15;
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}
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match_len += 7;
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}
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match_len += 3;
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for (i = 0; i < match_len; i++) {
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guint8 byte;
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if (match_off > wmem_array_get_count(obuf))
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return FALSE;
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if (wmem_array_try_index(obuf, wmem_array_get_count(obuf)-match_off, &byte))
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return FALSE;
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wmem_array_append_one(obuf, byte);
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}
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}
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}
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return TRUE;
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}
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tvbuff_t *
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tvb_uncompress_lz77(tvbuff_t *tvb, const int offset, int in_size)
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{
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volatile gboolean ok = FALSE;
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wmem_allocator_t *pool;
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wmem_array_t *obuf;
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tvbuff_t *out;
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pool = wmem_allocator_new(WMEM_ALLOCATOR_SIMPLE);
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obuf = wmem_array_sized_new(pool, 1, in_size*2);
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TRY {
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ok = do_uncompress(tvb, offset, in_size, obuf);
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} CATCH_ALL {
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ok = FALSE;
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}
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ENDTRY;
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if (ok) {
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/*
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* Cannot pass a tvb free callback that frees the wmem
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* pool, so we make an extra copy that uses bare
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* pointers. This could be optimized if tvb API had a
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* free pool callback of some sort.
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*/
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guint size = wmem_array_get_count(obuf);
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guint8 *p = (guint8 *)g_malloc(size);
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memcpy(p, wmem_array_get_raw(obuf), size);
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out = tvb_new_real_data(p, size, size);
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tvb_set_free_cb(out, g_free);
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} else {
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out = NULL;
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}
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wmem_destroy_allocator(pool);
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return out;
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}
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tvbuff_t *
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tvb_child_uncompress_lz77(tvbuff_t *parent, tvbuff_t *tvb, const int offset, int in_size)
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{
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tvbuff_t *new_tvb = tvb_uncompress_lz77(tvb, offset, in_size);
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if (new_tvb)
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tvb_set_child_real_data_tvbuff(parent, new_tvb);
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return new_tvb;
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}
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/*
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* Editor modelines - https://www.wireshark.org/tools/modelines.html
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*
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* Local variables:
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* c-basic-offset: 8
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* tab-width: 8
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* indent-tabs-mode: t
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* End:
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*
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* vi: set shiftwidth=8 tabstop=8 noexpandtab:
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* :indentSize=8:tabSize=8:noTabs=false:
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*/
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