Segmentation fault in binary seek function when processing malformed MPEG files due to null pointer dereference in index_entries array access.

[xdc]

## How to reproduce:
`
% avconv -ss 0.1 -i /workspace/POC/POC_libav_avconv_segfault_mpeg_seek -f null -
avconv version 13_dev0, Copyright (c) 2000-2018 the Libav developers

built on Jul 19 2025 14:57:50 with Ubuntu clang version 16.0.6 (++20231112100510+7cbf1a259152-1~exp1~20231112100554.106)
configuration: --cc=/Fuzzer/OPA++/afl-clang-lto --extra-cflags= --prefix=/workspace/benchmark/program/libav-c464278-Apr16-2019/install --disable-shared --enable-static --disable-x86asm --disable-inline-asm
libavutil 56. 8. 0 / 56. 8. 0
libavcodec 58. 12. 1 / 58. 12. 1
libavformat 58. 2. 0 / 58. 2. 0
libavdevice 57. 0. 2 / 57. 0. 2
libavfilter 7. 1. 0 / 7. 1. 0
libavresample 4. 0. 0 / 4. 0. 0
libswscale 5. 0. 1 / 5. 0. 1

[mpeg @ 0x555557165800] Format detected only with low score of 25, misdetection possible!
[mpeg @ 0x555557165800] Could not find codec parameters (Video: [0][0][0][0] / 0x0000

none)

[mpeg @ 0x555557165800] start time is not set in estimate_timings_from_pts
Segmentation fault (core dumped)
`

## GDB Analysis:
`
Program received signal SIGSEGV, Segmentation fault.
0x0000555555bfd3aa in ff_seek_frame_binary (s=0x555557165800, stream_index=0, target_ts=9000, flags=1) at libavformat/utils.c:1289
1289 e = &st->index_entries[index];
#0 0x0000555555bfd3aa in ff_seek_frame_binary (s=0x555557165800, stream_index=0, target_ts=9000, flags=1) at libavformat/utils.c:1289
#1 0x0000555555bfea54 in seek_frame_internal (stream_index=<optimized out>, timestamp=9000, s=<optimized out>, flags=<optimized out>) at libavformat/utils.c:1556
#2 av_seek_frame (s=0x555557165800, stream_index=<optimized out>, timestamp=<optimized out>, flags=1) at libavformat/utils.c:1567
#3 0x00005555558705b6 in open_input_file (o=0x7fffffffd380, filename=0x7fffffffe071 "/workspace/POC/POC_libav_avconv_segfault_mpeg_seek") at avtools/avconv_opt.c:835
#4 0x0000555555873a5b in open_files (l=0x555557153098, inout=0x5555555d4d9a "input", open_file=0x55555586f940 <open_input_file>) at avtools/avconv_opt.c:2467
#5 0x0000555555893816 in avconv_parse_options (argc=<optimized out>, argv=<optimized out>) at avtools/avconv_opt.c:2504
#6 main (argc=<optimized out>, argv=<optimized out>) at avtools/avconv.c:2953

Disassembly around crash point:

0x0000555555bfd38a <ff_seek_frame_binary+794>: mov $0x11d70,%edx
0x0000555555bfd38f <ff_seek_frame_binary+799>: sub %r8d,%edx
0x0000555555bfd392 <ff_seek_frame_binary+802>: mov (%r11),%rsi
0x0000555555bfd395 <ff_seek_frame_binary+805>: movzbl (%rsi,%rdx,1),%r8d
0x0000555555bfd39a <ff_seek_frame_binary+810>: add $0x1,%r8b
0x0000555555bfd39e <ff_seek_frame_binary+814>: adc $0x0,%r8b
0x0000555555bfd3a2 <ff_seek_frame_binary+818>: mov %r8b,(%rsi,%rdx,1)
0x0000555555bfd3a6 <ff_seek_frame_binary+822>: lea (%rdi,%rdi,2),%rdx

=> 0x0000555555bfd3aa <ff_seek_frame_binary+826>: mov (%rax,%rdx,8),%rcx <-- CRASH HERE

0x0000555555bfd3ae <ff_seek_frame_binary+830>: mov 0x8(%rax,%rdx,8),%r8

`

## Root Cause:
The crash occurs in ff_seek_frame_binary() function at libavformat/utils.c:1289 when attempting to access:
`c
e = &st->index_entries[index];
`

The issue is that:

1. The file is detected as MPEG format with low confidence score (25)
2. Codec parameters cannot be determined properly
3. The stream's index_entries array is NULL
4. The seek operation tries to access index_entries[index] without null checking

The malformed file causes the MPEG demuxer to enter an inconsistent state where seeking is attempted on a stream without proper index initialization.

## POC File:
The malformed file is available at: /workspace/POC/POC_libav_avconv_segfault_mpeg_seek​https://drive.google.com/file/d/1CX1GZUyJVzyDDGLVa8FG58XUt_30kHKT/view?usp=sharing

[mkver]

This is the FFmpeg bug tracker. Libav is (was) a fork of FFmpeg that is now dead. Fuzzing it is therefore pointless and reporting bugs for Libav here would be wrong even if Libav were not dead.