[Issue 22838] New: std.bitmanip.BitArray.count() reads beyond data when data size is integer size_t multiple

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=22838

          Issue ID: 22838
           Summary: std.bitmanip.BitArray.count() reads beyond data when
                    data size is integer size_t multiple
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: critical
          Priority: P1
         Component: phobos
          Assignee: nobody at puremagic.com
          Reporter: johanengelen at weka.io

Bug was found with AddressSanitizer. Report at the end.

The unittest that triggers the bug:
```
    @system @nogc unittest
    {
        size_t[2] buffer;
        BitArray b = BitArray(buffer[], buffer.sizeof * 8);

        b[] = true;
        b[0 .. 1] = true;
        b.flip();
        b.flip(1);
        cast(void) b.count();
    }
```

The bug happens on this line:
```
    size_t count() const @nogc pure nothrow
    {
        if (_ptr)
        {
            size_t bitCount;
            foreach (i; 0 .. fullWords)
                bitCount += countBitsSet(_ptr[i]);
            bitCount += countBitsSet(_ptr[fullWords] & endMask); // <---- BUG!
            return bitCount;
        }
        else
        {
            return 0;
        }
    }
```


```
==60514==ERROR: AddressSanitizer: stack-buffer-overflow on address
0x00016d251750 at pc 0x00010402fce0 bp 0x00016d251680 sp 0x00016d251678
READ of size 8 at 0x00016d251750 thread T0
    #0 0x10402fcdc in _D3std8bitmanip8BitArray5countMxFNaNbNiZm bitmanip.d:1450
    #1 0x1040509d8 in _D3std8bitmanip8BitArray20__unittest_L2753_C19FNiZv
bitmanip.d:2762
    #2 0x1040ca2a0 in _D3std8bitmanip10__unittestZ bitmanip.d
    #3 0x102bb2208 in
_D11test_runner7testAllFZ14__foreachbody2MFPS6object10ModuleInfoZi
test_runner.d:65
    #4 0x1094240dc in
_D6object10ModuleInfo7opApplyFMDFPSQBhQBdZiZ9__lambda2MFyPSQCfQCbZi
object.d:2476
    #5 0x10947466c in
_D2rt5minfo17moduleinfos_applyFMDFyPS6object10ModuleInfoZiZ14__foreachbody2MFKSQCz19sections_elf_shared3DSOZi
minfo.d:777
    #6 0x10947c38c in _D2rt19sections_elf_shared3DSO7opApplyFMDFKSQBqQBqQyZiZi
sections_elf_shared.d:112
    #7 0x109474254 in
_D2rt5minfo17moduleinfos_applyFMDFyPS6object10ModuleInfoZiZi minfo.d:770
    #8 0x10941cbb8 in _D6object10ModuleInfo7opApplyFMDFPSQBhQBdZiZi
object.d:2475
    #9 0x102bb1abc in _D11test_runner7testAllFZS4core7runtime14UnitTestResult
test_runner.d:63
    #10 0x102bb0fa4 in _D11test_runner6testerFZS4core7runtime14UnitTestResult
test_runner.d:33
    #11 0x1093ecaf4 in runModuleUnitTests runtime.d:580
    #12 0x10944d9ec in _D2rt6dmain212_d_run_main2UAAamPUQgZiZ6runAllMFZv
dmain2.d:487
    #13 0x10944d748 in _D2rt6dmain212_d_run_main2UAAamPUQgZiZ7tryExecMFMDFZvZv
dmain2.d:461
    #14 0x10944cefc in _d_run_main2 dmain2.d:520
    #15 0x10944c384 in _d_run_main dmain2.d:320
    #16 0x102bb280c in main entrypoint.d:42
    #17 0x1105cd0f0 in start+0x204 (dyld:arm64+0x50f0)
    #18 0x960c7ffffffffffc  (<unknown module>)

Address 0x00016d251750 is located in stack of thread T0 at offset 48 in frame
    #0 0x104050858 in _D3std8bitmanip8BitArray20__unittest_L2753_C19FNiZv
bitmanip.d:2753

  This frame has 2 object(s):
    [32, 48) '' <== Memory access at offset 48 overflows this variable
    [64, 80) ''
HINT: this may be a false positive if your program uses some custom stack
unwind mechanism, swapcontext or vfork
      (longjmp and C++ exceptions *are* supported)
SUMMARY: AddressSanitizer: stack-buffer-overflow bitmanip.d:1450 in
_D3std8bitmanip8BitArray5countMxFNaNbNiZm
Shadow bytes around the buggy address:
  0x00702da6a290: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x00702da6a2a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x00702da6a2b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x00702da6a2c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x00702da6a2d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x00702da6a2e0: 00 00 00 00 f1 f1 f1 f1 00 00[f2]f2 00 00 f3 f3
  0x00702da6a2f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x00702da6a300: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x00702da6a310: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x00702da6a320: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x00702da6a330: 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
  Shadow gap:              cc
==60514==ABORTING
```

--