## Description
There is a segment fault detected by AddressSanitizer

## System info
```
Ubuntu 20.04.2 LTS
clang version 12.0.0-++20210402082642+04ba60cfe598-1~exp1~20210402063359.71
MP4Box - GPAC version 1.1.0-DEV-rev1687-g16bd902cb-master
```

## Build command
```
./configure --static-mp4box --prefix=`realpath ./install` --enable-sanitizer --cc=clang --cxx=clang++
```

## crash command
```
MP4Box -frag 1 -out /dev/null poc_file
```

## Pocs
[poc.zip](https://github.com/gpac/gpac/files/7976870/poc.zip)



## Crash output
```
==15501==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x0000007ea282 bp 0x7ffc1a6c8090 sp 0x7ffc1a6c8080 T0)
==15501==The signal is caused by a READ memory access.
==15501==Hint: address points to the zero page.
    #0 0x7ea282 in gf_isom_get_media_data_size /programs/mp4box/builds/build6/src/isomedia/isom_read.c:3890:46
    #1 0x156a8a6 in isor_declare_track /programs/mp4box/builds/build6/src/filters/isoffin_load.c:637:70
    #2 0x1576c07 in isor_declare_objects /programs/mp4box/builds/build6/src/filters/isoffin_load.c:1446:3
    #3 0xcfd23d in isoffin_initialize /programs/mp4box/builds/build6/src/filters/isoffin_read.c:485:8
    #4 0xb70f63 in gf_filter_new_finalize /programs/mp4box/builds/build6/src/filter_core/filter.c:429:8
    #5 0xb6f83c in gf_filter_new /programs/mp4box/builds/build6/src/filter_core/filter.c:383:7
    #6 0xb5b5fe in gf_fs_load_filter_internal /programs/mp4box/builds/build6/src/filter_core/filter_session.c:1250:13
    #7 0x910798 in gf_media_fragment_file /programs/mp4box/builds/build6/src/media_tools/isom_tools.c:3784:6
    #8 0x4e6fcc in mp4boxMain /programs/mp4box/builds/build6/applications/mp4box/main.c:6455:7
    #9 0x7fc6744d50b2 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
    #10 0x41ea6d in _start (/programs/mp4box/builds/build6/bin/gcc/MP4Box+0x41ea6d)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV /programs/mp4box/builds/build6/src/isomedia/isom_read.c:3890:46 in gf_isom_get_media_data_size
==15501==ABORTING
```
There is a segment fault detected by AddressSanitizer
This is a GitHub Issue
repo:gpac
owner:gpac
Title : There is a segment fault detected by AddressSanitizer
Issue date:

--- start body ---
## Description
There is a segment fault detected by AddressSanitizer

## System info
```
Ubuntu 20.04.2 LTS
clang version 12.0.0-++20210402082642+04ba60cfe598-1~exp1~20210402063359.71
MP4Box - GPAC version 1.1.0-DEV-rev1687-g16bd902cb-master
```

## Build command
```
./configure --static-mp4box --prefix=`realpath ./install` --enable-sanitizer --cc=clang --cxx=clang++
```

## crash command
```
MP4Box -frag 1 -out /dev/null poc_file
```

## Pocs
[poc.zip](https://github.com/gpac/gpac/files/7976870/poc.zip)



## Crash output
```
==15501==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x0000007ea282 bp 0x7ffc1a6c8090 sp 0x7ffc1a6c8080 T0)
==15501==The signal is caused by a READ memory access.
==15501==Hint: address points to the zero page.
    #0 0x7ea282 in gf_isom_get_media_data_size /programs/mp4box/builds/build6/src/isomedia/isom_read.c:3890:46
    #1 0x156a8a6 in isor_declare_track /programs/mp4box/builds/build6/src/filters/isoffin_load.c:637:70
    #2 0x1576c07 in isor_declare_objects /programs/mp4box/builds/build6/src/filters/isoffin_load.c:1446:3
    #3 0xcfd23d in isoffin_initialize /programs/mp4box/builds/build6/src/filters/isoffin_read.c:485:8
    #4 0xb70f63 in gf_filter_new_finalize /programs/mp4box/builds/build6/src/filter_core/filter.c:429:8
    #5 0xb6f83c in gf_filter_new /programs/mp4box/builds/build6/src/filter_core/filter.c:383:7
    #6 0xb5b5fe in gf_fs_load_filter_internal /programs/mp4box/builds/build6/src/filter_core/filter_session.c:1250:13
    #7 0x910798 in gf_media_fragment_file /programs/mp4box/builds/build6/src/media_tools/isom_tools.c:3784:6
    #8 0x4e6fcc in mp4boxMain /programs/mp4box/builds/build6/applications/mp4box/main.c:6455:7
    #9 0x7fc6744d50b2 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
    #10 0x41ea6d in _start (/programs/mp4box/builds/build6/bin/gcc/MP4Box+0x41ea6d)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV /programs/mp4box/builds/build6/src/isomedia/isom_read.c:3890:46 in gf_isom_get_media_data_size
==15501==ABORTING
```
--- end body ---

A segmentation fault in the MP4Box application (GPAC version 1.1.0-DEV) is triggered by a crafted input file, leading to a potential Denial of Service (DoS). The crash occurs in the function gf_isom_get_media_data_size when attempting to read memory that is not allocated, indicating a vulnerability that could be exploited by providing specially crafted media files.