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avformat/matroskadec: Make reading zero-length elements spec-compliant 

For a very long time, the payload of integer and float elements had to
have a length > 0. Our parser treated such invalid elements as having a
value zero. But now it has been defined what an EBML element with length
zero means: It is a shorthand for the default value. This has also been
defined for strings (both ASCII and UTF-8). This commit modifies our
parser to support this.

Reviewed-by: Ridley Combs <rcombs@rcombs.me>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
This commit is contained in:
Andreas Rheinhardt 2021-02-16 16:51:40 +01:00
parent 2f1a5621d3
commit 0a99c3dadc
1 changed files with 33 additions and 17 deletions
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50
libavformat/matroskadec.c
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@ -929,12 +929,17 @@ static int ebml_read_length(MatroskaDemuxContext *matroska, AVIOContext *pb,
/*
* Read the next element as an unsigned int.
* Returns NEEDS_CHECKING.
* Returns NEEDS_CHECKING unless size == 0.
*/
static int ebml_read_uint(AVIOContext *pb, int size, uint64_t *num)
static int ebml_read_uint(AVIOContext *pb, int size,
uint64_t default_value, uint64_t *num)
{
int n = 0;
if (size == 0) {
*num = default_value;
return 0;
}
/* big-endian ordering; build up number */
*num = 0;
while (n++ < size)
@ -945,14 +950,16 @@ static int ebml_read_uint(AVIOContext *pb, int size, uint64_t *num)
/*
* Read the next element as a signed int.
* Returns NEEDS_CHECKING.
* Returns NEEDS_CHECKING unless size == 0.
*/
static int ebml_read_sint(AVIOContext *pb, int size, int64_t *num)
static int ebml_read_sint(AVIOContext *pb, int size,
int64_t default_value, int64_t *num)
{
int n = 1;
if (size == 0) {
*num = 0;
*num = default_value;
return 0;
} else {
*num = sign_extend(avio_r8(pb), 8);
@ -966,17 +973,19 @@ static int ebml_read_sint(AVIOContext *pb, int size, int64_t *num)
/*
* Read the next element as a float.
* Returns NEEDS_CHECKING or < 0 on obvious failure.
* Returns 0 if size == 0, NEEDS_CHECKING or < 0 on obvious failure.
*/
static int ebml_read_float(AVIOContext *pb, int size, double *num)
static int ebml_read_float(AVIOContext *pb, int size,
double default_value, double *num)
{
if (size == 0)
*num = 0;
else if (size == 4)
if (size == 0) {
*num = default_value;
return 0;
} else if (size == 4) {
*num = av_int2float(avio_rb32(pb));
else if (size == 8)
} else if (size == 8) {
*num = av_int2double(avio_rb64(pb));
else
} else
return AVERROR_INVALIDDATA;
return NEEDS_CHECKING;
@ -986,11 +995,17 @@ static int ebml_read_float(AVIOContext *pb, int size, double *num)
* Read the next element as an ASCII string.
* 0 is success, < 0 or NEEDS_CHECKING is failure.
*/
static int ebml_read_ascii(AVIOContext *pb, int size, char **str)
static int ebml_read_ascii(AVIOContext *pb, int size,
const char *default_value, char **str)
{
char *res;
int ret;
if (size == 0 && default_value) {
res = av_strdup(default_value);
if (!res)
return AVERROR(ENOMEM);
} else {
/* EBML strings are usually not 0-terminated, so we allocate one
* byte more, read the string and NULL-terminate it ourselves. */
if (!(res = av_malloc(size + 1)))
@ -1000,6 +1015,7 @@ static int ebml_read_ascii(AVIOContext *pb, int size, char **str)
return ret < 0 ? ret : NEEDS_CHECKING;
}
(res)[size] = '\0';
}
av_free(*str);
*str = res;
@ -1396,17 +1412,17 @@ static int ebml_parse(MatroskaDemuxContext *matroska,
switch (syntax->type) {
case EBML_UINT:
res = ebml_read_uint(pb, length, data);
res = ebml_read_uint(pb, length, syntax->def.u, data);
break;
case EBML_SINT:
res = ebml_read_sint(pb, length, data);
res = ebml_read_sint(pb, length, syntax->def.i, data);
break;
case EBML_FLOAT:
res = ebml_read_float(pb, length, data);
res = ebml_read_float(pb, length, syntax->def.f, data);
break;
case EBML_STR:
case EBML_UTF8:
res = ebml_read_ascii(pb, length, data);
res = ebml_read_ascii(pb, length, syntax->def.s, data);
break;
case EBML_BIN:
res = ebml_read_binary(pb, length, pos_alt, data);