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