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avformat/matroskadec: Redo level handling 

This commit changes how levels are handled: If the level used for
ebml_parse ends directly after an element that has been consumed, then
ebml_parse ends the level itself (and any known-length levels that end
there as well) and informs the caller via the return value; if the
current level is of unknown-length, then the level is ended as soon as
an element that is not valid on the current level, but on a higher
level is encountered (or if EOF has been encountered).

This is designed for situations where one wants to parse master elements
incrementally, i.e. not in one go via ebml_parse_nest.

The (incremental) parsing of clusters still mixes levels by using a
syntax list that contains elements from different levels and the level
is still ended manually via a call to ebml_level_end if the last cluster
was an unknown-length cluster (known-length clusters are already ended
when their last element is read), but only if the next element is a
cluster, too. A  different level 1 element following an unknown-length
cluster will currently simply be presumed to be part of the earlier
cluster. Fixing this will be done in a future patch. The modifications
to matroska_parse_cluster contained in this patch are only intended not
to cause regressions.

Nevertheless, the fact that known-length levels are automatically ended
in ebml_parse when their last element has been read already fixes a bogus
error message introduced in 9326117b that was emitted when a known-length
cluster is followed by another level 1 element other than a cluster in
which case the cluster's level was not ended (which only happened when
a new cluster has been encountered) so that the length check (introduced
in 9326117b) failed for the level 1 element as it is of course not
contained in the previous cluster. Most Matroska files were affected by
this.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
tags/n4.2
Andreas Rheinhardt James Almer 6 years ago
parent
c1abd95ad0
commit
b31c9b72e5
1 changed files with 82 additions and 21 deletions
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  1. +82
    -21
      libavformat/matroskadec.c

+ 82
- 21
libavformat/matroskadec.c View File

@@ -71,6 +71,8 @@
#define EBML_UNKNOWN_LENGTH UINT64_MAX /* EBML unknown length, in uint64_t */
#define NEEDS_CHECKING 2 /* Indicates that some error checks
* still need to be performed */
#define LEVEL_ENDED 3 /* return value of ebml_parse when the
* syntax level used for parsing ended. */

typedef enum {
EBML_NONE,
@@ -1087,7 +1089,7 @@ static EbmlSyntax *ebml_parse_id(EbmlSyntax *syntax, uint32_t id)
static int ebml_parse_nest(MatroskaDemuxContext *matroska, EbmlSyntax *syntax,
void *data)
{
int i, res = 0;
int i, res;

for (i = 0; syntax[i].id; i++)
switch (syntax[i].type) {
@@ -1112,10 +1114,16 @@ static int ebml_parse_nest(MatroskaDemuxContext *matroska, EbmlSyntax *syntax,
break;
}

while (!res && !ebml_level_end(matroska))
if (!matroska->levels[matroska->num_levels - 1].length) {
matroska->num_levels--;
return 0;
}

do {
res = ebml_parse(matroska, syntax, data);
} while (!res);

return res;
return res == LEVEL_ENDED ? 0 : res;
}

static int is_ebml_id_valid(uint32_t id)
@@ -1184,17 +1192,26 @@ static int ebml_parse(MatroskaDemuxContext *matroska,
uint32_t id;
uint64_t length;
int64_t pos = avio_tell(pb);
int res, update_pos = 1;
int res, update_pos = 1, level_check;
void *newelem;
MatroskaLevel1Element *level1_elem;
MatroskaLevel *level = matroska->num_levels ? &matroska->levels[matroska->num_levels - 1] : NULL;

if (!matroska->current_id) {
uint64_t id;
res = ebml_read_num(matroska, pb, 4, &id, 0);
if (res < 0) {
// in live mode, finish parsing if EOF is reached.
return (matroska->is_live && pb->eof_reached &&
res == AVERROR_EOF) ? 1 : res;
if (pb->eof_reached && res == AVERROR_EOF) {
if (matroska->is_live)
// in live mode, finish parsing if EOF is reached.
return 1;
if (level && level->length == EBML_UNKNOWN_LENGTH && pos == avio_tell(pb)) {
// Unknown-length levels automatically end at EOF.
matroska->num_levels--;
return LEVEL_ENDED;
}
}
return res;
}
matroska->current_id = id | 1 << 7 * res;
} else
@@ -1203,13 +1220,22 @@ static int ebml_parse(MatroskaDemuxContext *matroska,
id = matroska->current_id;

syntax = ebml_parse_id(syntax, id);
if (!syntax->id && id == MATROSKA_ID_CLUSTER &&
matroska->num_levels > 0 &&
matroska->levels[matroska->num_levels - 1].length == EBML_UNKNOWN_LENGTH)
return 0; // we reached the end of an unknown size cluster
if (!syntax->id && id != EBML_ID_VOID && id != EBML_ID_CRC32) {
av_log(matroska->ctx, AV_LOG_DEBUG, "Unknown entry 0x%"PRIX32"\n", id);
update_pos = 0;
if (level && level->length == EBML_UNKNOWN_LENGTH) {
// Unknown-length levels end when an element from an upper level
// in the hierarchy is encountered.
while (syntax->def.n) {
syntax = ebml_parse_id(syntax->def.n, id);
if (syntax->id) {
matroska->num_levels--;
return LEVEL_ENDED;
}
};
}

av_log(matroska->ctx, AV_LOG_DEBUG, "Unknown entry 0x%"PRIX32" at pos. "
"%"PRId64"\n", id, pos);
update_pos = 0; /* Don't update resync_pos as an error might have happened. */
}

data = (char *) data + syntax->data_offset;
@@ -1244,26 +1270,34 @@ static int ebml_parse(MatroskaDemuxContext *matroska,
uint64_t elem_end = pos + length,
level_end = level->start + level->length;

if (level_end < elem_end) {
if (elem_end < level_end) {
level_check = 0;
} else if (elem_end == level_end) {
level_check = LEVEL_ENDED;
} else {
av_log(matroska->ctx, AV_LOG_ERROR,
"Element at 0x%"PRIx64" ending at 0x%"PRIx64" exceeds "
"containing master element ending at 0x%"PRIx64"\n",
pos, elem_end, level_end);
return AVERROR_INVALIDDATA;
}
} else if (length != EBML_UNKNOWN_LENGTH) {
level_check = 0;
} else if (level->length != EBML_UNKNOWN_LENGTH) {
av_log(matroska->ctx, AV_LOG_ERROR, "Unknown-sized element "
"at 0x%"PRIx64" inside parent with finite size\n", pos);
return AVERROR_INVALIDDATA;
} else if (length == EBML_UNKNOWN_LENGTH && id != MATROSKA_ID_CLUSTER) {
} else if (id != MATROSKA_ID_CLUSTER) {
// According to the specifications only clusters and segments
// are allowed to be unknown-sized.
av_log(matroska->ctx, AV_LOG_ERROR,
"Found unknown-sized element other than a cluster at "
"0x%"PRIx64". Dropping the invalid element.\n", pos);
return AVERROR_INVALIDDATA;
}
}
} else
level_check = 0;
} else
level_check = 0;

if (update_pos) {
// We have found an element that is allowed at this place
@@ -1304,7 +1338,9 @@ static int ebml_parse(MatroskaDemuxContext *matroska,
av_log(matroska->ctx, AV_LOG_ERROR, "Duplicate element\n");
level1_elem->parsed = 1;
}
return ebml_parse_nest(matroska, syntax->def.n, data);
if (res = ebml_parse_nest(matroska, syntax->def.n, data))
return res;
break;
case EBML_STOP:
return 1;
default:
@@ -1336,7 +1372,7 @@ static int ebml_parse(MatroskaDemuxContext *matroska,
else
res = AVERROR_EOF;
} else
res = 0;
goto level_check;
}

if (res == AVERROR_INVALIDDATA)
@@ -1347,8 +1383,24 @@ static int ebml_parse(MatroskaDemuxContext *matroska,
av_log(matroska->ctx, AV_LOG_ERROR, "File ended prematurely\n");
res = AVERROR(EIO);
}

return res;
}
return res;

level_check:
if (level_check == LEVEL_ENDED && matroska->num_levels) {
level = &matroska->levels[matroska->num_levels - 1];
pos = avio_tell(pb);

// Given that pos >= level->start no check for
// level->length != EBML_UNKNOWN_LENGTH is necessary.
while (matroska->num_levels && pos == level->start + level->length) {
matroska->num_levels--;
level--;
}
}

return level_check;
}

static void ebml_free(EbmlSyntax *syntax, void *data)
@@ -1707,6 +1759,10 @@ static int matroska_parse_seekhead_entry(MatroskaDemuxContext *matroska,
matroska->current_id = 0;

ret = ebml_parse(matroska, matroska_segment, matroska);
if (ret == LEVEL_ENDED) {
/* This can only happen if the seek brought us beyond EOF. */
ret = AVERROR_EOF;
}
}
}
/* Seek back - notice that in all instances where this is used it is safe
@@ -3567,9 +3623,11 @@ static int matroska_parse_cluster(MatroskaDemuxContext *matroska)
res = ebml_parse(matroska,
matroska_cluster_parsing,
cluster);
else
cluster->pos = 0;
}

if (!res && block->bin.size > 0) {
if (res >= 0 && block->bin.size > 0) {
int is_keyframe = block->non_simple ? block->reference == INT64_MIN : -1;
uint8_t* additional = block->additional.size > 0 ?
block->additional.data : NULL;
@@ -3584,6 +3642,9 @@ static int matroska_parse_cluster(MatroskaDemuxContext *matroska)
block->discard_padding);
}

if (res == LEVEL_ENDED)
cluster->pos = 0;

ebml_free(matroska_blockgroup, block);
memset(block, 0, sizeof(*block));



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