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mpv/demux/ebml.c
wm4 496d53a2f2 ebml: warn if an EBML has unknown length 
While unknown lengths are supported in some important cases like
segments and clusters, they are not for small and complex metadata
elements like the track list. Such elements are simply rejected.

This case was caught by the size sanity check below, but the message is
misleading and wrong.

(There are likely no files in the wild which require support for this.
The sample file I've seen was muxed by libavformat, but in a case where
it aborted when writing the header. Clearly a broken file.)
2015-09-03 13:39:00 +02:00

651 lines
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/*
* native ebml reader for the Matroska demuxer
* new parser copyright (c) 2010 Uoti Urpala
* copyright (c) 2004 Aurelien Jacobs <aurel@gnuage.org>
* based on the one written by Ronald Bultje for gstreamer
*
* This file is part of mpv.
*
* mpv is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* mpv is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with mpv. If not, see <http://www.gnu.org/licenses/>.
*/
#include "config.h"
#include <stdlib.h>
#include <stdbool.h>
#include <inttypes.h>
#include <stddef.h>
#include <assert.h>
#include <libavutil/intfloat.h>
#include <libavutil/common.h>
#include "talloc.h"
#include "ebml.h"
#include "stream/stream.h"
#include "common/msg.h"
// Whether the id is a known Matroska level 1 element (allowed as element on
// global file level, after the level 0 MATROSKA_ID_SEGMENT).
// This (intentionally) doesn't include "global" elements.
bool ebml_is_mkv_level1_id(uint32_t id)
{
switch (id) {
case MATROSKA_ID_SEEKHEAD:
case MATROSKA_ID_INFO:
case MATROSKA_ID_CLUSTER:
case MATROSKA_ID_TRACKS:
case MATROSKA_ID_CUES:
case MATROSKA_ID_ATTACHMENTS:
case MATROSKA_ID_CHAPTERS:
case MATROSKA_ID_TAGS:
return true;
default:
return false;
}
}
/*
* Read: the element content data ID.
* Return: the ID.
*/
uint32_t ebml_read_id(stream_t *s)
{
int i, len_mask = 0x80;
uint32_t id;
for (i = 0, id = stream_read_char(s); i < 4 && !(id & len_mask); i++)
len_mask >>= 1;
if (i >= 4)
return EBML_ID_INVALID;
while (i--)
id = (id << 8) | stream_read_char(s);
return id;
}
/*
* Read a variable length unsigned int.
*/
uint64_t ebml_read_vlen_uint(bstr *buffer)
{
int i, j, num_ffs = 0, len_mask = 0x80;
uint64_t num;
if (buffer->len == 0)
return EBML_UINT_INVALID;
for (i = 0, num = buffer->start[0]; i < 8 && !(num & len_mask); i++)
len_mask >>= 1;
if (i >= 8)
return EBML_UINT_INVALID;
j = i + 1;
if ((int) (num &= (len_mask - 1)) == len_mask - 1)
num_ffs++;
if (j > buffer->len)
return EBML_UINT_INVALID;
for (int n = 0; n < i; n++) {
num = (num << 8) | buffer->start[n + 1];
if ((num & 0xFF) == 0xFF)
num_ffs++;
}
if (j == num_ffs)
return EBML_UINT_INVALID;
buffer->start += j;
buffer->len -= j;
return num;
}
/*
* Read a variable length signed int.
*/
int64_t ebml_read_vlen_int(bstr *buffer)
{
uint64_t unum;
int l;
/* read as unsigned number first */
size_t len = buffer->len;
unum = ebml_read_vlen_uint(buffer);
if (unum == EBML_UINT_INVALID)
return EBML_INT_INVALID;
l = len - buffer->len;
return unum - ((1 << ((7 * l) - 1)) - 1);
}
/*
* Read: element content length.
*/
uint64_t ebml_read_length(stream_t *s)
{
int i, j, num_ffs = 0, len_mask = 0x80;
uint64_t len;
for (i = 0, len = stream_read_char(s); i < 8 && !(len & len_mask); i++)
len_mask >>= 1;
if (i >= 8)
return EBML_UINT_INVALID;
j = i + 1;
if ((int) (len &= (len_mask - 1)) == len_mask - 1)
num_ffs++;
while (i--) {
len = (len << 8) | stream_read_char(s);
if ((len & 0xFF) == 0xFF)
num_ffs++;
}
if (j == num_ffs)
return EBML_UINT_INVALID;
if (len >= 1ULL<<63) // Can happen if stream_read_char returns EOF
return EBML_UINT_INVALID;
return len;
}
/*
* Read the next element as an unsigned int.
*/
uint64_t ebml_read_uint(stream_t *s)
{
uint64_t len, value = 0;
len = ebml_read_length(s);
if (len == EBML_UINT_INVALID || len > 8)
return EBML_UINT_INVALID;
while (len--)
value = (value << 8) | stream_read_char(s);
return value;
}
/*
* Read the next element as a signed int.
*/
int64_t ebml_read_int(stream_t *s)
{
uint64_t value = 0;
uint64_t len;
int l;
len = ebml_read_length(s);
if (len == EBML_UINT_INVALID || len > 8)
return EBML_INT_INVALID;
if (!len)
return 0;
len--;
l = stream_read_char(s);
if (l & 0x80)
value = -1;
value = (value << 8) | l;
while (len--)
value = (value << 8) | stream_read_char(s);
return (int64_t)value; // assume complement of 2
}
/*
* Skip the current element.
* end: the end of the parent element or -1 (for robust error handling)
*/
int ebml_read_skip(struct mp_log *log, int64_t end, stream_t *s)
{
uint64_t len;
int64_t pos = stream_tell(s);
len = ebml_read_length(s);
if (len == EBML_UINT_INVALID)
goto invalid;
int64_t pos2 = stream_tell(s);
if (len >= INT64_MAX - pos2 || (end > 0 && pos2 + len > end))
goto invalid;
if (!stream_skip(s, len))
goto invalid;
return 0;
invalid:
mp_err(log, "Invalid EBML length at position %"PRId64"\n", pos);
stream_seek(s, pos);
return 1;
}
/*
* Skip to (probable) next cluster (MATROSKA_ID_CLUSTER) element start position.
*/
int ebml_resync_cluster(struct mp_log *log, stream_t *s)
{
int64_t pos = stream_tell(s);
uint32_t last_4_bytes = 0;
if (!s->eof) {
mp_err(log, "Corrupt file detected. "
"Trying to resync starting from position %"PRId64"...\n", pos);
}
while (!s->eof) {
// Assumes MATROSKA_ID_CLUSTER is 4 bytes, with no 0 bytes.
if (last_4_bytes == MATROSKA_ID_CLUSTER) {
mp_err(log, "Cluster found at %"PRId64".\n", pos - 4);
stream_seek(s, pos - 4);
return 0;
}
last_4_bytes = (last_4_bytes << 8) | stream_read_char(s);
pos++;
}
return -1;
}
#define EVALARGS(F, ...) F(__VA_ARGS__)
#define E(str, N, type) const struct ebml_elem_desc ebml_ ## N ## _desc = { str, type };
#define E_SN(str, count, N) const struct ebml_elem_desc ebml_ ## N ## _desc = { str, EBML_TYPE_SUBELEMENTS, sizeof(struct ebml_ ## N), count, (const struct ebml_field_desc[]){
#define E_S(str, count) EVALARGS(E_SN, str, count, N)
#define FN(id, name, multiple, N) { id, multiple, offsetof(struct ebml_ ## N, name), offsetof(struct ebml_ ## N, n_ ## name), &ebml_##name##_desc},
#define F(id, name, multiple) EVALARGS(FN, id, name, multiple, N)
#include "ebml_defs.c"
#undef EVALARGS
#undef SN
#undef S
#undef FN
#undef F
// Used to read/write pointers to different struct types
struct generic;
#define generic_struct struct generic
static uint32_t ebml_parse_id(uint8_t *data, size_t data_len, int *length)
{
*length = -1;
uint8_t *end = data + data_len;
if (data == end)
return EBML_ID_INVALID;
int len = 1;
uint32_t id = *data++;
for (int len_mask = 0x80; !(id & len_mask); len_mask >>= 1) {
len++;
if (len > 4)
return EBML_ID_INVALID;
}
*length = len;
while (--len && data < end)
id = (id << 8) | *data++;
return id;
}
static uint64_t ebml_parse_length(uint8_t *data, size_t data_len, int *length)
{
*length = -1;
uint8_t *end = data + data_len;
if (data == end)
return -1;
uint64_t r = *data++;
int len = 1;
int len_mask;
for (len_mask = 0x80; !(r & len_mask); len_mask >>= 1) {
len++;
if (len > 8)
return -1;
}
r &= len_mask - 1;
int num_allones = 0;
if (r == len_mask - 1)
num_allones++;
for (int i = 1; i < len; i++) {
if (data == end)
return -1;
if (*data == 255)
num_allones++;
r = (r << 8) | *data++;
}
// According to Matroska specs this means "unknown length"
// Could be supported if there are any actual files using it
if (num_allones == len)
return -1;
*length = len;
return r;
}
static uint64_t ebml_parse_uint(uint8_t *data, int length)
{
assert(length >= 0 && length <= 8);
uint64_t r = 0;
while (length--)
r = (r << 8) + *data++;
return r;
}
static int64_t ebml_parse_sint(uint8_t *data, int length)
{
assert(length >= 0 && length <= 8);
if (!length)
return 0;
uint64_t r = 0;
if (*data & 0x80)
r = -1;
while (length--)
r = (r << 8) | *data++;
return (int64_t)r; // assume complement of 2
}
static double ebml_parse_float(uint8_t *data, int length)
{
assert(length == 0 || length == 4 || length == 8);
uint64_t i = ebml_parse_uint(data, length);
if (length == 4)
return av_int2float(i);
else
return av_int2double(i);
}
// target must be initialized to zero
static void ebml_parse_element(struct ebml_parse_ctx *ctx, void *target,
uint8_t *data, int size,
const struct ebml_elem_desc *type, int level)
{
assert(type->type == EBML_TYPE_SUBELEMENTS);
assert(level < 8);
MP_DBG(ctx, "%.*sParsing element %s\n", level, " ", type->name);
char *s = target;
uint8_t *end = data + size;
uint8_t *p = data;
int num_elems[MAX_EBML_SUBELEMENTS] = {0};
while (p < end) {
uint8_t *startp = p;
int len;
uint32_t id = ebml_parse_id(p, end - p, &len);
if (len > end - p)
goto past_end_error;
if (len < 0) {
MP_DBG(ctx, "Error parsing subelement id\n");
goto other_error;
}
p += len;
uint64_t length = ebml_parse_length(p, end - p, &len);
if (len > end - p)
goto past_end_error;
if (len < 0) {
MP_DBG(ctx, "Error parsing subelement length\n");
goto other_error;
}
p += len;
int field_idx = -1;
for (int i = 0; i < type->field_count; i++)
if (type->fields[i].id == id) {
field_idx = i;
num_elems[i]++;
if (num_elems[i] >= 0x70000000) {
MP_ERR(ctx, "Too many EBML subelements.\n");
goto other_error;
}
break;
}
if (length > end - p) {
if (field_idx >= 0 && type->fields[field_idx].desc->type
!= EBML_TYPE_SUBELEMENTS) {
MP_DBG(ctx, "Subelement content goes "
"past end of containing element\n");
goto other_error;
}
// Try to parse what is possible from inside this partial element
ctx->has_errors = true;
length = end - p;
}
p += length;
continue;
past_end_error:
MP_DBG(ctx, "Subelement headers go past end of containing element\n");
other_error:
ctx->has_errors = true;
end = startp;
break;
}
for (int i = 0; i < type->field_count; i++) {
if (num_elems[i] && type->fields[i].multiple) {
char *ptr = s + type->fields[i].offset;
switch (type->fields[i].desc->type) {
case EBML_TYPE_SUBELEMENTS: {
size_t max = 1000000000 / type->fields[i].desc->size;
if (num_elems[i] > max) {
MP_ERR(ctx, "Too many subelements.\n");
num_elems[i] = max;
}
int sz = num_elems[i] * type->fields[i].desc->size;
*(generic_struct **) ptr = talloc_zero_size(ctx->talloc_ctx, sz);
break;
}
case EBML_TYPE_UINT:
*(uint64_t **) ptr = talloc_zero_array(ctx->talloc_ctx,
uint64_t, num_elems[i]);
break;
case EBML_TYPE_SINT:
*(int64_t **) ptr = talloc_zero_array(ctx->talloc_ctx,
int64_t, num_elems[i]);
break;
case EBML_TYPE_FLOAT:
*(double **) ptr = talloc_zero_array(ctx->talloc_ctx,
double, num_elems[i]);
break;
case EBML_TYPE_STR:
*(char ***) ptr = talloc_zero_array(ctx->talloc_ctx,
char *, num_elems[i]);
break;
case EBML_TYPE_BINARY:
*(struct bstr **) ptr = talloc_zero_array(ctx->talloc_ctx,
struct bstr,
num_elems[i]);
break;
case EBML_TYPE_EBML_ID:
*(int32_t **) ptr = talloc_zero_array(ctx->talloc_ctx,
uint32_t, num_elems[i]);
break;
default:
abort();
}
}
}
while (data < end) {
int len;
uint32_t id = ebml_parse_id(data, end - data, &len);
if (len < 0 || len > end - data) {
MP_DBG(ctx, "Error parsing subelement\n");
break;
}
data += len;
uint64_t length = ebml_parse_length(data, end - data, &len);
if (len < 0 || len > end - data) {
MP_DBG(ctx, "Error parsing subelement length\n");
break;
}
data += len;
if (length > end - data) {
// Try to parse what is possible from inside this partial element
length = end - data;
MP_DBG(ctx, "Next subelement content goes "
"past end of containing element, will be truncated\n");
}
int field_idx = -1;
for (int i = 0; i < type->field_count; i++)
if (type->fields[i].id == id) {
field_idx = i;
break;
}
if (field_idx < 0) {
if (id == 0xec)
MP_DBG(ctx, "%.*sIgnoring Void element "
"size: %"PRIu64"\n", level+1, " ", length);
else if (id == 0xbf)
MP_DBG(ctx, "%.*sIgnoring CRC-32 "
"element size: %"PRIu64"\n", level+1, " ",
length);
else
MP_DBG(ctx, "Ignoring unrecognized "
"subelement. ID: %x size: %"PRIu64"\n", id, length);
data += length;
continue;
}
const struct ebml_field_desc *fd = &type->fields[field_idx];
const struct ebml_elem_desc *ed = fd->desc;
bool multiple = fd->multiple;
int *countptr = (int *) (s + fd->count_offset);
if (*countptr >= num_elems[field_idx]) {
// Shouldn't happen with on any sane file without bugs
MP_ERR(ctx, "Too many subelems?\n");
ctx->has_errors = true;
data += length;
continue;
}
if (*countptr > 0 && !multiple) {
MP_DBG(ctx, "Another subelement of type "
"%x %s (size: %"PRIu64"). Only one allowed. Ignoring.\n",
id, ed->name, length);
ctx->has_errors = true;
data += length;
continue;
}
MP_DBG(ctx, "%.*sParsing %x %s size: %"PRIu64
" value: ", level+1, " ", id, ed->name, length);
char *fieldptr = s + fd->offset;
switch (ed->type) {
case EBML_TYPE_SUBELEMENTS:
MP_DBG(ctx, "subelements\n");
char *subelptr;
if (multiple) {
char *array_start = (char *) *(generic_struct **) fieldptr;
subelptr = array_start + *countptr * ed->size;
} else
subelptr = fieldptr;
ebml_parse_element(ctx, subelptr, data, length, ed, level + 1);
break;
case EBML_TYPE_UINT:;
uint64_t *uintptr;
#define GETPTR(subelptr, fieldtype) \
if (multiple) \
subelptr = *(fieldtype **) fieldptr + *countptr; \
else \
subelptr = (fieldtype *) fieldptr
GETPTR(uintptr, uint64_t);
if (length < 1 || length > 8) {
MP_DBG(ctx, "uint invalid length %"PRIu64"\n", length);
goto error;
}
*uintptr = ebml_parse_uint(data, length);
MP_DBG(ctx, "uint %"PRIu64"\n", *uintptr);
break;
case EBML_TYPE_SINT:;
int64_t *sintptr;
GETPTR(sintptr, int64_t);
if (length > 8) {
MP_DBG(ctx, "sint invalid length %"PRIu64"\n", length);
goto error;
}
*sintptr = ebml_parse_sint(data, length);
MP_DBG(ctx, "sint %"PRId64"\n", *sintptr);
break;
case EBML_TYPE_FLOAT:;
double *floatptr;
GETPTR(floatptr, double);
if (length != 0 && length != 4 && length != 8) {
MP_DBG(ctx, "float invalid length %"PRIu64"\n", length);
goto error;
}
*floatptr = ebml_parse_float(data, length);
MP_DBG(ctx, "float %f\n", *floatptr);
break;
case EBML_TYPE_STR:
if (length > 1024 * 1024) {
MP_ERR(ctx, "Not reading overly long string element.\n");
break;
}
char **strptr;
GETPTR(strptr, char *);
*strptr = talloc_strndup(ctx->talloc_ctx, data, length);
MP_DBG(ctx, "string \"%s\"\n", *strptr);
break;
case EBML_TYPE_BINARY:;
if (length > 0x80000000) {
MP_ERR(ctx, "Not reading overly long EBML element.\n");
break;
}
struct bstr *binptr;
GETPTR(binptr, struct bstr);
binptr->start = data;
binptr->len = length;
MP_DBG(ctx, "binary %zd bytes\n", binptr->len);
break;
case EBML_TYPE_EBML_ID:;
uint32_t *idptr;
GETPTR(idptr, uint32_t);
*idptr = ebml_parse_id(data, end - data, &len);
if (len != length) {
MP_DBG(ctx, "ebml_id broken value\n");
goto error;
}
MP_DBG(ctx, "ebml_id %x\n", (unsigned)*idptr);
break;
default:
abort();
}
*countptr += 1;
error:
data += length;
}
}
// target must be initialized to zero
int ebml_read_element(struct stream *s, struct ebml_parse_ctx *ctx,
void *target, const struct ebml_elem_desc *desc)
{
ctx->has_errors = false;
int msglevel = ctx->no_error_messages ? MSGL_DEBUG : MSGL_WARN;
uint64_t length = ebml_read_length(s);
if (s->eof) {
MP_MSG(ctx, msglevel, "Unexpected end of file "
"- partial or corrupt file?\n");
return -1;
}
if (length == EBML_UINT_INVALID) {
MP_MSG(ctx, msglevel, "EBML element with unknown length - unsupported\n");
return -1;
}
if (length > 1000000000) {
MP_MSG(ctx, msglevel, "Refusing to read element over 100 MB in size\n");
return -1;
}
ctx->talloc_ctx = talloc_size(NULL, length);
int read_len = stream_read(s, ctx->talloc_ctx, length);
if (read_len < length)
MP_MSG(ctx, msglevel, "Unexpected end of file - partial or corrupt file?\n");
ebml_parse_element(ctx, target, ctx->talloc_ctx, read_len, desc, 0);
if (ctx->has_errors)
MP_MSG(ctx, msglevel, "Error parsing element %s\n", desc->name);
return 0;
}
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