LibreDWG v0.12.4.4608 was discovered to contain a heap buffer overflow via the function dwg_add_object at decode.c.
### system info
Ubuntu x86_64, clang 6.0, dwg2dxf([0.12.4.4608](https://github.com/LibreDWG/libredwg/releases/tag/0.12.4.4608))

### Command line
./programs/dwg2dxf -b -m @@ -o /dev/null

### AddressSanitizer output
==8995==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x62e00000ac80 at pc 0x0000004bc125 bp 0x7fffffffc7c0 sp 0x7fffffffbf70
WRITE of size 168 at 0x62e00000ac80 thread T0
    #0 0x4bc124 in __asan_memset /fuzzer/build/llvm_tools/llvm-4.0.0.src/projects/compiler-rt/lib/asan/asan_interceptors.cc:457
    #1 0x5a062e in dwg_add_object /testcase/libredwg/src/decode.c:4740:3
    #2 0x7e0942 in dwg_add_VIEW /testcase/libredwg/src/dwg_api.c:24619:3
    #3 0x70c71e in decode_preR13_section /testcase/libredwg/src/decode_r11.c:434:13
    #4 0x705d7a in decode_preR13 /testcase/libredwg/src/decode_r11.c:834:12
    #5 0x53245a in dwg_decode /testcase/libredwg/src/decode.c:209:23
    #6 0x50d759 in dwg_read_file /testcase/libredwg/src/dwg.c:254:11
    #7 0x50c454 in main /testcase/libredwg/programs/dwg2dxf.c:258:15
    #8 0x7ffff6e22c86 in __libc_start_main /build/glibc-CVJwZb/glibc-2.27/csu/../csu/libc-start.c:310
    #9 0x419ee9 in _start (/testcase/libredwg/programs/dwg2dxf+0x419ee9)

0x62e00000ac80 is located 0 bytes to the right of 43136-byte region [0x62e000000400,0x62e00000ac80)
allocated by thread T0 here:
    #0 0x4d2968 in realloc /fuzzer/build/llvm_tools/llvm-4.0.0.src/projects/compiler-rt/lib/asan/asan_malloc_linux.cc:79
    #1 0x70b9ca in decode_preR13_section /testcase/libredwg/src/decode_r11.c:273:32
    #2 0x705d7a in decode_preR13 /testcase/libredwg/src/decode_r11.c:834:12
    #3 0x50d759 in dwg_read_file /testcase/libredwg/src/dwg.c:254:11
    #4 0x50c454 in main /testcase/libredwg/programs/dwg2dxf.c:258:15
    #5 0x7ffff6e22c86 in __libc_start_main /build/glibc-CVJwZb/glibc-2.27/csu/../csu/libc-start.c:310

SUMMARY: AddressSanitizer: heap-buffer-overflow /fuzzer/build/llvm_tools/llvm-4.0.0.src/projects/compiler-rt/lib/asan/asan_interceptors.cc:457 in __asan_memset
Shadow bytes around the buggy address:
  0x0c5c7fff9540: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c5c7fff9550: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c5c7fff9560: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c5c7fff9570: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c5c7fff9580: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c5c7fff9590:[fa]fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c5c7fff95a0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c5c7fff95b0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c5c7fff95c0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c5c7fff95d0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c5c7fff95e0: 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
==8995==ABORTING
### poc
https://gitee.com/cxlzff/fuzz-poc/raw/master/libredwg/dwg_add_object_bof


heap-buffer-overflow exists in the function dwg_add_object in decode.c
This is a GitHub Issue
repo:libredwg
owner:LibreDWG
Title : heap-buffer-overflow exists in the function dwg_add_object in decode.c
Issue date:

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### system info
Ubuntu x86_64, clang 6.0, dwg2dxf([0.12.4.4608](https://github.com/LibreDWG/libredwg/releases/tag/0.12.4.4608))

### Command line
./programs/dwg2dxf -b -m @@ -o /dev/null

### AddressSanitizer output
==8995==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x62e00000ac80 at pc 0x0000004bc125 bp 0x7fffffffc7c0 sp 0x7fffffffbf70
WRITE of size 168 at 0x62e00000ac80 thread T0
    #0 0x4bc124 in __asan_memset /fuzzer/build/llvm_tools/llvm-4.0.0.src/projects/compiler-rt/lib/asan/asan_interceptors.cc:457
    #1 0x5a062e in dwg_add_object /testcase/libredwg/src/decode.c:4740:3
    #2 0x7e0942 in dwg_add_VIEW /testcase/libredwg/src/dwg_api.c:24619:3
    #3 0x70c71e in decode_preR13_section /testcase/libredwg/src/decode_r11.c:434:13
    #4 0x705d7a in decode_preR13 /testcase/libredwg/src/decode_r11.c:834:12
    #5 0x53245a in dwg_decode /testcase/libredwg/src/decode.c:209:23
    #6 0x50d759 in dwg_read_file /testcase/libredwg/src/dwg.c:254:11
    #7 0x50c454 in main /testcase/libredwg/programs/dwg2dxf.c:258:15
    #8 0x7ffff6e22c86 in __libc_start_main /build/glibc-CVJwZb/glibc-2.27/csu/../csu/libc-start.c:310
    #9 0x419ee9 in _start (/testcase/libredwg/programs/dwg2dxf+0x419ee9)

0x62e00000ac80 is located 0 bytes to the right of 43136-byte region [0x62e000000400,0x62e00000ac80)
allocated by thread T0 here:
    #0 0x4d2968 in realloc /fuzzer/build/llvm_tools/llvm-4.0.0.src/projects/compiler-rt/lib/asan/asan_malloc_linux.cc:79
    #1 0x70b9ca in decode_preR13_section /testcase/libredwg/src/decode_r11.c:273:32
    #2 0x705d7a in decode_preR13 /testcase/libredwg/src/decode_r11.c:834:12
    #3 0x50d759 in dwg_read_file /testcase/libredwg/src/dwg.c:254:11
    #4 0x50c454 in main /testcase/libredwg/programs/dwg2dxf.c:258:15
    #5 0x7ffff6e22c86 in __libc_start_main /build/glibc-CVJwZb/glibc-2.27/csu/../csu/libc-start.c:310

SUMMARY: AddressSanitizer: heap-buffer-overflow /fuzzer/build/llvm_tools/llvm-4.0.0.src/projects/compiler-rt/lib/asan/asan_interceptors.cc:457 in __asan_memset
Shadow bytes around the buggy address:
  0x0c5c7fff9540: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c5c7fff9550: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c5c7fff9560: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c5c7fff9570: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c5c7fff9580: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c5c7fff9590:[fa]fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c5c7fff95a0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c5c7fff95b0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c5c7fff95c0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c5c7fff95d0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c5c7fff95e0: 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
==8995==ABORTING
### poc
https://gitee.com/cxlzff/fuzz-poc/raw/master/libredwg/dwg_add_object_bof


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