heap overflow in rpmoffs

[asarubbo]

The following crafted iso causes an overflow in makedeltaiso

Command to reproduce:

makedeltaiso CRAFTED.iso CRAFTED.iso NEW.iso

Full trace:

ERROR: AddressSanitizer: heap-buffer-overflow on address 0x602000000032 at pc 0x000000421b4a bp 0x7ffe5ac9abf0 sp 0x7ffe5ac9abe8
READ of size 4 at 0x602000000032 thread T0
    #0 0x421b49 in rpmoffs /root/drpm/deltarpm/rpmoffs.c:168
    #1 0x403263 in main /root/drpm/deltarpm/makedeltaiso.c:587
    #2 0x7efcd01431f6 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
    #3 0x7efcd01432ab in __libc_start_main_impl ../csu/libc-start.c:381
    #4 0x4057b0 in _start (/usr/bin/makedeltaiso+0x4057b0)

0x602000000032 is located 0 bytes to the right of 2-byte region [0x602000000030,0x602000000032)
allocated by thread T0 here:
    #0 0x7efcd03ce4ff in __interceptor_malloc /var/tmp/portage/sys-devel/gcc-11.3.1_p20221209/work/gcc-11-20221209/libsanitizer/asan/asan_malloc_linux.cpp:145
    #1 0x41e048 in rpmoffs /root/drpm/deltarpm/rpmoffs.c:137
    #2 0x403263 in main /root/drpm/deltarpm/makedeltaiso.c:587
    #3 0x7efcd01431f6 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58

SUMMARY: AddressSanitizer: heap-buffer-overflow /root/drpm/deltarpm/rpmoffs.c:168 in rpmoffs
Shadow bytes around the buggy address:
  0x0c047fff7fb0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c047fff7fc0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c047fff7fd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c047fff7fe0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c047fff7ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c047fff8000: fa fa 00 02 fa fa[02]fa fa fa fa fa fa fa fa fa
  0x0c047fff8010: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8020: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8030: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8040: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8050: 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
==12731==ABORTING

Testcase attached here:
file.zip

I tested the package at the following commit:
1e76473