The binary MP4Box in Gpac 1.0.1 has a double-free vulnerability in the avc_compute_poc function in av_parsers.c, which allows attackers to cause a denial of service, even code execution and escalation of privileges.
- [x] I looked for a similar issue and couldn't find any.
- [x] I tried with the latest version of GPAC. Installers available at http://gpac.io/downloads/gpac-nightly-builds/
- [x] I give enough information for contributors to reproduce my issue (meaningful title, github labels, platform and compiler, command-line ...). 

Hi, there.

There is a segmentation fault caused by buffer overflow in avc_compute_poc, av_parsers.c:5988 in commit  592ba2689a3.

Here is my environment, compiler info and gpac version:
~~~~
Distributor ID:	Ubuntu
Description:	Ubuntu 16.04.6 LTS
Release:	16.04
Codename:	xenial
gcc: 5.4.0

MP4Box - GPAC version 1.1.0-DEV-rev1170-g592ba26-master
(c) 2000-2021 Telecom Paris distributed under LGPL v2.1+ - http://gpac.io
	MINI build (encoders, decoders, audio and video output disabled)

Please cite our work in your research:
	GPAC Filters: https://doi.org/10.1145/3339825.3394929
	GPAC: https://doi.org/10.1145/1291233.1291452

GPAC Configuration: --static-bin --enable-debug
Features: GPAC_CONFIG_LINUX GPAC_64_BITS GPAC_HAS_SOCK_UN GPAC_MINIMAL_ODF GPAC_HAS_QJS GPAC_HAS_FREETYPE GPAC_HAS_JPEG GPAC_HAS_PNG  GPAC_DISABLE_3D
~~~~

To reproduce, run
~~~~
./MP4Box -info poc
~~~~

POC:
[poc.zip](https://github.com/gpac/gpac/files/7065639/mp4box-seg-overflow_avc_compute_poc5988.zip)
(unzip first)

Program output:
~~~~
[Core] exp-golomb read failed, not enough bits in bitstream !
[Core] exp-golomb read failed, not enough bits in bitstream !
[Core] exp-golomb read failed, not enough bits in bitstream !
[Core] exp-golomb read failed, not enough bits in bitstream !
[Core] exp-golomb read failed, not enough bits in bitstream !
[avc-h264] offset_for_ref_frame overflow from poc_cycle_length
[AVC|H264] Warning: Error parsing NAL unit
[AVC|H264] Error parsing Sequence Param Set
[Core] exp-golomb read failed, not enough bits in bitstream !
[Core] exp-golomb read failed, not enough bits in bitstream !
[Core] exp-golomb read failed, not enough bits in bitstream !
[Core] exp-golomb read failed, not enough bits in bitstream !
Segmentation fault (core dumped)
~~~~

Here is the trace reported by gdb:
~~~~
Stopped reason: SIGSEGV
gef➤  bt
#0  0x0000000000b82f00 in avc_compute_poc (si=si@entry=0x7fffffff5020) at /mnt/data/playground/gpac/src/media_tools/av_parsers.c:5988
#1  0x0000000000bce182 in gf_avc_parse_nalu (bs=<optimized out>, avc=0x24ae050) at /mnt/data/playground/gpac/src/media_tools/av_parsers.c:6191
#2  0x000000000144109d in naludmx_parse_nal_avc (is_islice=<synthetic pointer>, is_slice=<synthetic pointer>, skip_nal=<synthetic pointer>, nal_type=0x3, size=0xf, data=0x248dfba "Cd\234\316s", <incomplete sequence \350>, ctx=0x24ada70) at /mnt/data/playground/gpac/src/filters/reframe_nalu.c:2348
#3  naludmx_process (filter=0x24a0bd0) at /mnt/data/playground/gpac/src/filters/reframe_nalu.c:2874
#4  0x0000000000fe4c18 in gf_filter_process_task (task=0x2492ed0) at /mnt/data/playground/gpac/src/filter_core/filter.c:2441
#5  0x0000000000f7b909 in gf_fs_thread_proc (sess_thread=sess_thread@entry=0x248c2b0) at /mnt/data/playground/gpac/src/filter_core/filter_session.c:1640
#6  0x0000000000f93558 in gf_fs_run (fsess=fsess@entry=0x248c220) at /mnt/data/playground/gpac/src/filter_core/filter_session.c:1877
#7  0x0000000000c18b4b in gf_media_import (importer=importer@entry=0x7fffffff5bf0) at /mnt/data/playground/gpac/src/media_tools/media_import.c:1178
#8  0x0000000000497345 in convert_file_info (inName=0x7fffffffe159 "tmp", trackID=0x0) at /mnt/data/playground/gpac/applications/mp4box/fileimport.c:128
#9  0x0000000000456aaa in mp4boxMain (argc=<optimized out>, argv=<optimized out>) at /mnt/data/playground/gpac/applications/mp4box/main.c:5925
#10 0x0000000001f06bb6 in generic_start_main ()
#11 0x0000000001f071a5 in __libc_start_main ()
#12 0x000000000041c4e9 in _start ()
~~~~

The reason for this bug is that the program does not check whether the length of a buffer fit its actual size.
<img width="922" alt="image" src="https://user-images.githubusercontent.com/7632714/131101665-2c1728e7-19c6-48af-ba1c-832d2f2d6a2e.png">


Segmentation fault caused by buffer overflow using mp4box in avc_compute_poc, av_parsers.c:5988
This is a GitHub Issue
repo:gpac
owner:gpac
Title : Segmentation fault caused by buffer overflow using mp4box in avc_compute_poc, av_parsers.c:5988
Issue date:

--- start body ---
- [x] I looked for a similar issue and couldn't find any.
- [x] I tried with the latest version of GPAC. Installers available at http://gpac.io/downloads/gpac-nightly-builds/
- [x] I give enough information for contributors to reproduce my issue (meaningful title, github labels, platform and compiler, command-line ...). 

Hi, there.

There is a segmentation fault caused by buffer overflow in avc_compute_poc, av_parsers.c:5988 in commit  592ba2689a3.

Here is my environment, compiler info and gpac version:
~~~~
Distributor ID:	Ubuntu
Description:	Ubuntu 16.04.6 LTS
Release:	16.04
Codename:	xenial
gcc: 5.4.0

MP4Box - GPAC version 1.1.0-DEV-rev1170-g592ba26-master
(c) 2000-2021 Telecom Paris distributed under LGPL v2.1+ - http://gpac.io
	MINI build (encoders, decoders, audio and video output disabled)

Please cite our work in your research:
	GPAC Filters: https://doi.org/10.1145/3339825.3394929
	GPAC: https://doi.org/10.1145/1291233.1291452

GPAC Configuration: --static-bin --enable-debug
Features: GPAC_CONFIG_LINUX GPAC_64_BITS GPAC_HAS_SOCK_UN GPAC_MINIMAL_ODF GPAC_HAS_QJS GPAC_HAS_FREETYPE GPAC_HAS_JPEG GPAC_HAS_PNG  GPAC_DISABLE_3D
~~~~

To reproduce, run
~~~~
./MP4Box -info poc
~~~~

POC:
[poc.zip](https://github.com/gpac/gpac/files/7065639/mp4box-seg-overflow_avc_compute_poc5988.zip)
(unzip first)

Program output:
~~~~
[Core] exp-golomb read failed, not enough bits in bitstream !
[Core] exp-golomb read failed, not enough bits in bitstream !
[Core] exp-golomb read failed, not enough bits in bitstream !
[Core] exp-golomb read failed, not enough bits in bitstream !
[Core] exp-golomb read failed, not enough bits in bitstream !
[avc-h264] offset_for_ref_frame overflow from poc_cycle_length
[AVC|H264] Warning: Error parsing NAL unit
[AVC|H264] Error parsing Sequence Param Set
[Core] exp-golomb read failed, not enough bits in bitstream !
[Core] exp-golomb read failed, not enough bits in bitstream !
[Core] exp-golomb read failed, not enough bits in bitstream !
[Core] exp-golomb read failed, not enough bits in bitstream !
Segmentation fault (core dumped)
~~~~

Here is the trace reported by gdb:
~~~~
Stopped reason: SIGSEGV
gef➤  bt
#0  0x0000000000b82f00 in avc_compute_poc (si=si@entry=0x7fffffff5020) at /mnt/data/playground/gpac/src/media_tools/av_parsers.c:5988
#1  0x0000000000bce182 in gf_avc_parse_nalu (bs=<optimized out>, avc=0x24ae050) at /mnt/data/playground/gpac/src/media_tools/av_parsers.c:6191
#2  0x000000000144109d in naludmx_parse_nal_avc (is_islice=<synthetic pointer>, is_slice=<synthetic pointer>, skip_nal=<synthetic pointer>, nal_type=0x3, size=0xf, data=0x248dfba "Cd\234\316s", <incomplete sequence \350>, ctx=0x24ada70) at /mnt/data/playground/gpac/src/filters/reframe_nalu.c:2348
#3  naludmx_process (filter=0x24a0bd0) at /mnt/data/playground/gpac/src/filters/reframe_nalu.c:2874
#4  0x0000000000fe4c18 in gf_filter_process_task (task=0x2492ed0) at /mnt/data/playground/gpac/src/filter_core/filter.c:2441
#5  0x0000000000f7b909 in gf_fs_thread_proc (sess_thread=sess_thread@entry=0x248c2b0) at /mnt/data/playground/gpac/src/filter_core/filter_session.c:1640
#6  0x0000000000f93558 in gf_fs_run (fsess=fsess@entry=0x248c220) at /mnt/data/playground/gpac/src/filter_core/filter_session.c:1877
#7  0x0000000000c18b4b in gf_media_import (importer=importer@entry=0x7fffffff5bf0) at /mnt/data/playground/gpac/src/media_tools/media_import.c:1178
#8  0x0000000000497345 in convert_file_info (inName=0x7fffffffe159 "tmp", trackID=0x0) at /mnt/data/playground/gpac/applications/mp4box/fileimport.c:128
#9  0x0000000000456aaa in mp4boxMain (argc=<optimized out>, argv=<optimized out>) at /mnt/data/playground/gpac/applications/mp4box/main.c:5925
#10 0x0000000001f06bb6 in generic_start_main ()
#11 0x0000000001f071a5 in __libc_start_main ()
#12 0x000000000041c4e9 in _start ()
~~~~

The reason for this bug is that the program does not check whether the length of a buffer fit its actual size.
<img width="922" alt="image" src="https://user-images.githubusercontent.com/7632714/131101665-2c1728e7-19c6-48af-ba1c-832d2f2d6a2e.png">


--- end body ---
