##### Issue submission checklist

 - [X] I report the issue, it's not a question
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       forum.opencv.org, Stack Overflow, etc and have not found any solution
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 - [X ] There is reproducer code and related data files: videos, images, onnx, etc
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   The best reproducer -- test case for OpenCV that we can add to the library.
   Recommendations for media files and binary files:
   * Try to reproduce the issue with images and videos in opencv_extra repository
     to reduce attachment size
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     issue
   * Attach the image as an archive to the ticket, if you report some reader issue.
     Image hosting services compress images and it breaks the repro code.
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     if you report ONNX parsing or handling issue. Architecture details diagram
     from netron tool can be very useful too. See https://lutzroeder.github.io/netron/
   -->

#include "opencv2/core.hpp"

using namespace cv;

std::string Input1 { 0x00, 0x2f, 0x4a, 0x4a, 0x50, 0x4a, 0x4a };
std::string Input1Path = "Input1";

void assign_file(const char *Path, const char *Data, unsigned Size) {
  if (!Path)
    return;

  FILE *FP = fopen(Path, "wb");
  if (!FP)
    return;

  fwrite(Data, Size, 1, FP);
  fclose(FP);
}

int main(int argc, char* argv[]) {
  assign_file(Input1Path.c_str(), Input1.c_str(), Input1.size());

  try {
    FileStorage fs(Input1Path, FileStorage::READ); // Crash
  } catch(std::exception &E) {}
  return 0;
}

mkdir -p build && cd build
cmake -DBUILD_SHARED_LIBS=OFF -DOPENCV_ENABLE_ALLOCATOR_STATS=OFF -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ -DCMAKE_AR=/bin/llvm-ar -DCMAKE_C_FLAGS="-fsanitize=address,fuzzer-no-link -fno-omit-frame-pointer -g" -DCMAKE_CXX_FLAGS="-fsanitize=address,fuzzer-no-link -fno-omit-frame-pointer -g" -DCMAKE_EXE_LINKER_FLAGS="-fsanitize=address,fuzzer-no-link -fno-omit-frame-pointer -g" -DCMAKE_SHARED_LINKER_FLAGS="-fsanitize=address,fuzzer-no-link -fno-omit-frame-pointer -g" ..
make -j16

    for (;;) {
        int count = (int) std::min(buffer.size() - ofs - 16, maxCount);
        char *ptr = getsFromFile(&buffer[ofs], count + 1); // buffer is { 0x00, 0x2f, 0x4a, 0x4a, 0x50, 0x4a, 0x4a }, ptr points 0x00
        if (!ptr)
            break;
        int delta = (int) strlen(ptr); // delta is 0
        ofs += delta;
        maxCount -= delta;
        if (ptr[delta - 1] == '\n' || maxCount == 0) // ptr[delta - 1]: ptr[-1] -> heap buffer overflow
            break;
        if (delta == count)
            buffer.resize((size_t) (buffer.size() * 1.5));
    }
    return ofs > 0 ? &buffer[0] : 0;

==13614==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x6040000003cf at pc 0x0000004e06eb bp 0x7ffeb04ab1d0 sp 0x7ffeb04ab1c8
READ of size 1 at 0x6040000003cf thread T0
    #0 0x4e06ea in cv::FileStorage::Impl::gets(unsigned long) /root/fuzz-test-generation/exp/opencv/modules/core/src/persistence.cpp:820:13
    #1 0x4d6e15 in cv::FileStorage::Impl::open(char const*, int, char const*) /root/fuzz-test-generation/exp/opencv/modules/core/src/persistence.cpp:680:27
    #2 0x4fb9a8 in cv::FileStorage::FileStorage(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) /root/fuzz-test-generation/exp/opencv/modules/core/src/persistence.cpp:1850:18
    #3 0x4cbdda in main (/root/fuzz-test-generation/exp/opencv/fuzzer/filestorage/crash1/crash1+0x4cbdda)
    #4 0x7fdd17053bf6 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21bf6)
    #5 0x421429 in _start (/root/fuzz-test-generation/exp/opencv/fuzzer/filestorage/crash1/crash1+0x421429)

0x6040000003cf is located 1 bytes to the left of 40-byte region [0x6040000003d0,0x6040000003f8)
allocated by thread T0 here:
    #0 0x4c92dd in operator new(unsigned long) (/root/fuzz-test-generation/exp/opencv/fuzzer/filestorage/crash1/crash1+0x4c92dd)
    #1 0x4cf226 in __gnu_cxx::new_allocator<char>::allocate(unsigned long, void const*) /usr/lib/gcc/x86_64-linux-gnu/7.5.0/../../../../include/c++/7.5.0/ext/new_allocator.h:111:27
    #2 0x4cf226 in std::allocator_traits<std::allocator<char> >::allocate(std::allocator<char>&, unsigned long) /usr/lib/gcc/x86_64-linux-gnu/7.5.0/../../../../include/c++/7.5.0/bits/alloc_traits.h:436:20
    #3 0x4cf226 in std::_Vector_base<char, std::allocator<char> >::_M_allocate(unsigned long) /usr/lib/gcc/x86_64-linux-gnu/7.5.0/../../../../include/c++/7.5.0/bits/stl_vector.h:172:20
    #4 0x4cf226 in std::vector<char, std::allocator<char> >::_M_default_append(unsigned long) /usr/lib/gcc/x86_64-linux-gnu/7.5.0/../../../../include/c++/7.5.0/bits/vector.tcc:571:34
    #5 0x4cf226 in std::vector<char, std::allocator<char> >::resize(unsigned long) /usr/lib/gcc/x86_64-linux-gnu/7.5.0/../../../../include/c++/7.5.0/bits/stl_vector.h:692:4
    #6 0x4d6b59 in cv::FileStorage::Impl::open(char const*, int, char const*) /root/fuzz-test-generation/exp/opencv/modules/core/src/persistence.cpp:671:16
    #7 0x4fb9a8 in cv::FileStorage::FileStorage(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) /root/fuzz-test-generation/exp/opencv/modules/core/src/persistence.cpp:1850:18
    #8 0x4cbdda in main (/root/fuzz-test-generation/exp/opencv/fuzzer/filestorage/crash1/crash1+0x4cbdda)
    #9 0x7fdd17053bf6 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21bf6)

SUMMARY: AddressSanitizer: heap-buffer-overflow /root/fuzz-test-generation/exp/opencv/modules/core/src/persistence.cpp:820:13 in cv::FileStorage::Impl::gets(unsigned long)
Shadow bytes around the buggy address:
  0x0c087fff8020: fa fa fd fd fd fd fd fa fa fa fd fd fd fd fd fa
  0x0c087fff8030: fa fa fd fd fd fd fd fd fa fa fd fd fd fd fd fa
  0x0c087fff8040: fa fa fd fd fd fd fd fd fa fa fd fd fd fd fd fa
  0x0c087fff8050: fa fa fd fd fd fd fd fa fa fa fd fd fd fd fd fd
  0x0c087fff8060: fa fa fd fd fd fd fd fa fa fa fd fd fd fd fd fa
=>0x0c087fff8070: fa fa fd fd fd fd fd fd fa[fa]00 00 00 00 00 fa
  0x0c087fff8080: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff8090: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff80a0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff80b0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff80c0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
  Shadow gap:              cc
==13614==ABORTING