possible buffer overflow for FixedBuffer

[charlesxsh]

Example:

fn main() {
     let mut buffer = fixed_ring_buffer::fixed_buffer::FixedBuffer::alloc(1);
    buffer.write_at(&[1,2,3,4], 4, 100);
}

Result:

$ RUSTFLAGS=-Zsanitizer=address cargo run

=================================================================
==187352==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x602000000094 at pc 0x5566b8f17c52 bp 0x7ffd733c7140 sp 0x7ffd733c6910
...
SUMMARY: AddressSanitizer: heap-buffer-overflow (...) (BuildId: fb1f45dacd5ba7c097dc22ba42c33c71b5dbc90a) 
Shadow bytes around the buggy address:
  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 05 fa fa fa 01 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
  0x0c047fff8060: 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
==187352==ABORTING