Bug 22838 – std.bitmanip.BitArray.count() reads beyond data when data size is integer size_t multiple

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 ```

@JohanEngelen created dlang/phobos pull request #8400 "Fix 22838 - BitArray.count reads beyond data" fixing this issue: - Fix 22838 - BitArray.count reads beyond data This fixes issue 22838 https://issues.dlang.org/show_bug.cgi?id=22838 https://github.com/dlang/phobos/pull/8400

@JohanEngelen created dlang/phobos pull request #8401 "Fix 22838 - BitArray.count reads beyond data" fixing this issue: - Fix 22838 - BitArray.count reads beyond data This fixes issue 22838 https://issues.dlang.org/show_bug.cgi?id=22838 All hail AddressSanitizer! ;-) https://github.com/dlang/phobos/pull/8401

dlang/phobos pull request #8401 "Fix 22838 - BitArray.count reads beyond data" was merged into stable: - 292c38c43267829c7776e27d71da962eebeae405 by Johan Engelen: Fix 22838 - BitArray.count reads beyond data This fixes issue 22838 https://issues.dlang.org/show_bug.cgi?id=22838 All hail AddressSanitizer! ;-) https://github.com/dlang/phobos/pull/8401