heap-buffer-overflow found?

[Cvjark]

sample here:
heap-bufferoverflow-pos-)%at pdfalto.zip

Describe info：

$ ./pdfalto heap-bufferoverflow-pos-\>at\ pdfalto.cc\:190\:5

==43072==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x6040000000f1 at pc 0x00000043f92b bp 0x7fff65e8f0f0 sp 0x7fff65e8e8a0
WRITE of size 33 at 0x6040000000f1 thread T0
    #0 0x43f92a in strncat /home/bupt/Desktop/tools/llvm-12.0.1/llvm/projects/compiler-rt/lib/asan/asan_interceptors.cpp:397
    #1 0x503603 in main /home/bupt/Desktop/pdfalto/src/pdfalto.cc:190:5
    #2 0x7f8cfec7dc86 in __libc_start_main /build/glibc-CVJwZb/glibc-2.27/csu/../csu/libc-start.c:310
    #3 0x422ca9 in _start (/home/bupt/Desktop/pdfalto/build/pdfalto+0x422ca9)

0x6040000000f1 is located 0 bytes to the right of 33-byte region [0x6040000000d0,0x6040000000f1)
allocated by thread T0 here:
    #0 0x4b5270 in malloc /home/bupt//tools/llvm-12.0.1/llvm/projects/compiler-rt/lib/asan/asan_malloc_linux.cpp:145
    #1 0x5035f1 in main /home/bupt/Desktop/pdfalto/src/pdfalto.cc:189:22
    #2 0x7f8cfec7dc86 in __libc_start_main /build/glibc-CVJwZb/glibc-2.27/csu/../csu/libc-start.c:310

SUMMARY: AddressSanitizer: heap-buffer-overflow /home/bupt//tools/llvm-12.0.1/llvm/projects/compiler-rt/lib/asan/asan_interceptors.cpp:397 in strncat
Shadow bytes around the buggy address:
  0x0c087fff7fc0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c087fff7fd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c087fff7fe0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c087fff7ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c087fff8000: fa fa fd fd fd fd fd fd fa fa 00 00 00 00 00 04
=>0x0c087fff8010: fa fa 00 00 00 00 00 01 fa fa 00 00 00 00[01]fa
  0x0c087fff8020: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff8030: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff8040: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff8050: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff8060: 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
==43072==ABORTING