stack-buffer-overflow in strcpy::test::two

[riking]

This test appears to intentionally corrupt memory:

	#[test]
	fn two() {
		let src = b"hi\0";
		let mut dest = [0u8; 2]; // no space for null terminator
		let result = unsafe { strcpy(dest.as_mut_ptr(), src.as_ptr()) };
		assert_eq!(unsafe { core::slice::from_raw_parts(result, 2) }, b"hi");
	}

https://asan.saethlin.dev/ub?crate=tinyrlibc&version=0.3.0

test strcpy::test::two ... =================================================================
==12736==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffb5f9f7eb2 at pc 0x559635b472fc bp 0x7ffba02f4830 sp 0x7ffba02f4828
WRITE of size 1 at 0x7ffb5f9f7eb2 thread T29
    #0 0x559635b472fb in strcpy /build/src/strcpy.rs:13:3
    #1 0x559635b4b057 in tinyrlibc::strcpy::test::two::h743566c6ea54f540 /build/src/strcpy.rs:42:25
    #2 0x559635b4af02 in tinyrlibc::strcpy::test::two::_$u7b$$u7b$closure$u7d$$u7d$::hd19b72cfcca7882c /build/src/strcpy.rs:39:10

Address 0x7ffb5f9f7eb2 is located in stack of thread T29 at offset 178 in frame
    #0 0x559635b4af2f in tinyrlibc::strcpy::test::two::h743566c6ea54f540 /build/src/strcpy.rs:39

  This frame has 4 object(s):
    [32, 80) '_17' (line 43)
    [112, 128) '_11' (line 43)
    [144, 160) '_9' (line 43)
    [176, 178) 'dest' (line 41) <== Memory access at offset 178 overflows this variable

SUMMARY: AddressSanitizer: stack-buffer-overflow /build/src/strcpy.rs:13:3 in strcpy
Shadow bytes around the buggy address:
  0x7ffb5f9f7c00: f1 f1 f1 f1 00 00 00 f2 f2 f2 f2 f2 00 00 00 f2
  0x7ffb5f9f7c80: f2 f2 f2 f2 00 00 00 f3 f3 f3 f3 f3 00 00 00 00
  0x7ffb5f9f7d00: f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5
  0x7ffb5f9f7d80: f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5
  0x7ffb5f9f7e00: f1 f1 f1 f1 f8 f8 f8 f8 f8 f8 f2 f2 f2 f2 f8 f8
=>0x7ffb5f9f7e80: f2 f2 f8 f8 f2 f2[02]f3 00 00 00 00 00 00 00 00
  0x7ffb5f9f7f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x7ffb5f9f7f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x7ffb5f9f8000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x7ffb5f9f8080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x7ffb5f9f8100: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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
==12736==ABORTING

Fix: Don't write tests that intentionally trigger undefined behavior.

[thejpster]

Thank you for identifying this buggy test. Clearly putting 3 bytes in a 2 byte array is a mistake.

You are very welcome to submit a PR to fix the test.