Issue #13075 has been reported by Kazuki Yamaguchi.

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Bug #13075: String#unpack with block / String#unpack1 exposes uninitialized memory
https://bugs.ruby-lang.org/issues/13075

* Author: Kazuki Yamaguchi
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 
* Backport: 2.1: REQUIRED, 2.2: REQUIRED, 2.3: REQUIRED, 2.4: REQUIRED
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A problematic code looks like (in pack.c, pack_unpack_internal()):

~~~c
          case 'b':
            {
                VALUE bitstr;
                char *t;
                int bits;
                long i;

                if (p[-1] == '*' || len > (send - s) * 8)
                    len = (send - s) * 8;
                bits = 0;
                UNPACK_PUSH(bitstr = rb_usascii_str_new(0, len));
                t = RSTRING_PTR(bitstr);
                for (i=0; i<len; i++) {
                    if (i & 7) bits >>= 1;
                    else bits = (unsigned char)*s++;
                    *t++ = (bits & 1) ? '1' : '0';
                }
            }
            break;
~~~

UNPACK_PUSH() immediately yields the value (String#unpack with block) or returns to the caller (String#unpack1), but the content bytes are not initialized at the time.

This bug dates back to r11175 (Ruby 1.9.0).



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