Windows device read failure through Python file interface with read buffering enabled

Bug report

Bug description:

Attempting to read the last 16 sectors from a Windows device through the Python file interface fails unexpectedly when buffering is enabled. Those same sectors seem to be accessible without issue through the WIN32 file API itself.

I've included minimal reproduction code. To demonstrate this, configure DEVICE_SECTOR_CNT and DEVICE_PATH to match a drive attached to your system:

import win32file

DEVICE_PATH = "\\\\.\\PhysicalDrive3"
DEVICE_SECTOR_CNT = 62333952
DEVICE_SECTOR_SIZ = 512

for DEVICE_SECTOR_CHK in [DEVICE_SECTOR_CNT - 16, DEVICE_SECTOR_CNT - 15]:

	print("Read sector " + str(DEVICE_SECTOR_CHK) + " through win32file:")
	try:
		handle = win32file.CreateFile(
			DEVICE_PATH,
			win32file.GENERIC_READ | win32file.GENERIC_WRITE,
			win32file.FILE_SHARE_READ | win32file.FILE_SHARE_WRITE,
			None,
			win32file.OPEN_EXISTING,
			0,
			None
		)
		win32file.SetFilePointer(handle, DEVICE_SECTOR_CHK * DEVICE_SECTOR_SIZ, win32file.FILE_BEGIN)
		(_, result) = win32file.ReadFile(handle, DEVICE_SECTOR_SIZ)
		print(" ".join(["{:02X}".format(x) for x in result]))
	finally:
		win32file.CloseHandle(handle)

	print("Read sector " + str(DEVICE_SECTOR_CHK) + " through open:")
	with open(DEVICE_PATH, "rb") as device:
		device.seek(DEVICE_SECTOR_CHK * DEVICE_SECTOR_SIZ)
		result = device.read(DEVICE_SECTOR_SIZ)
		print(" ".join(["{:02X}".format(x) for x in result]))

Testing this with any drive attached to my system, I see a result like:

Read sector 62333936 through win32file:
FD FF F3 FF FB FF F3 FF F9 FF F8 FF FF FF FB FF 01 00 01 00 03 00 02 00 07 00 05 00 09 00 02 00 06 00 03 00 04 00 02 00 08 00 06 00 0C 00 08 00 0D 00 07 00 0B 00 07 00 0B 00 04 00 0E 00 05 00 0D 00 04 00 0C 00 06 00 0B 00 07 00 0C 00 08 00 0D 00 07 00 0D 00 07 00 0D 00 08 00 0B 00 05 00 0B 00 04 00 0F 00 06 00 13 00 0C 00 15 00 10 00 16 00 0F 00 14 00 0E 00 14 00 0F 00 16 00 0E 00 16 00 0F 00 17 00 10 00 15 00 10 00 11 00 0F 00 13 00 0A 00 14 00 06 00 13 00 09 00 12 00 0C 00 15 00 08 00 11 00 06 00 13 00 06 00 14 00 0A 00 12 00 0D 00 14 00 0A 00 0E 00 07 00 0F 00 04 00 11 00 06 00 0F 00 08 00 0D 00 0C 00 0D 00 0A 00 0F 00 03 00 0D 00 FF FF 0B 00 FD FF 09 00 FF FF 08 00 04 00 07 00 01 00 0A 00 00 00 0C 00 FD FF 0B 00 FC FF 06 00 FE FF 02 00 FD FF 01 00 FC FF 06 00 FD FF 09 00 FA FF 06 00 FD FF 04 00 FF FF 01 00 F9 FF FE FF FC FF FF FF F8 FF 02 00 F7 FF 01 00 F7 FF FE FF FA FF FE FF F6 FF FD FF F5 FF FD FF F5 FF FB FF F5 FF FC FF F4 FF FC FF FA FF FC FF FB FF FF FF FD FF FE FF FA FF 03 00 FE FF 04 00 FD FF FD FF FD FF 01 00 FC FF 02 00 FE FF 01 00 FC FF 02 00 F8 FF 00 00 F7 FF FF FF FB FF 00 00 FB FF 01 00 F5 FF FE FF F7 FF FD FF FA FF FE FF F9 FF 00 00 F7 FF FF FF F8 FF FF FF F9 FF 01 00 F3 FF 00 00 F5 FF FE FF F7 FF FF FF F5 FF FF FF F7 FF 01 00 FD FF 00 00 FA FF FC FF F5 FF F9 FF F3 FF FB FF F2 FF FC FF F3 FF FE FF F9 FF 01 00 FD FF FE FF FE FF FF FF F4 FF FF FF F0 FF FC FF F1 FF FF FF F8 FF 03 00 04 00 04 00 03 00 06 00 FD FF 04 00 F6 FF FC FF F5 FF F8 FF F5 FF F9 FF F9 FF FC FF FD FF 02 00 FB FF 05 00 FA FF
Read sector 62333936 through open:
FD FF F3 FF FB FF F3 FF F9 FF F8 FF FF FF FB FF 01 00 01 00 03 00 02 00 07 00 05 00 09 00 02 00 06 00 03 00 04 00 02 00 08 00 06 00 0C 00 08 00 0D 00 07 00 0B 00 07 00 0B 00 04 00 0E 00 05 00 0D 00 04 00 0C 00 06 00 0B 00 07 00 0C 00 08 00 0D 00 07 00 0D 00 07 00 0D 00 08 00 0B 00 05 00 0B 00 04 00 0F 00 06 00 13 00 0C 00 15 00 10 00 16 00 0F 00 14 00 0E 00 14 00 0F 00 16 00 0E 00 16 00 0F 00 17 00 10 00 15 00 10 00 11 00 0F 00 13 00 0A 00 14 00 06 00 13 00 09 00 12 00 0C 00 15 00 08 00 11 00 06 00 13 00 06 00 14 00 0A 00 12 00 0D 00 14 00 0A 00 0E 00 07 00 0F 00 04 00 11 00 06 00 0F 00 08 00 0D 00 0C 00 0D 00 0A 00 0F 00 03 00 0D 00 FF FF 0B 00 FD FF 09 00 FF FF 08 00 04 00 07 00 01 00 0A 00 00 00 0C 00 FD FF 0B 00 FC FF 06 00 FE FF 02 00 FD FF 01 00 FC FF 06 00 FD FF 09 00 FA FF 06 00 FD FF 04 00 FF FF 01 00 F9 FF FE FF FC FF FF FF F8 FF 02 00 F7 FF 01 00 F7 FF FE FF FA FF FE FF F6 FF FD FF F5 FF FD FF F5 FF FB FF F5 FF FC FF F4 FF FC FF FA FF FC FF FB FF FF FF FD FF FE FF FA FF 03 00 FE FF 04 00 FD FF FD FF FD FF 01 00 FC FF 02 00 FE FF 01 00 FC FF 02 00 F8 FF 00 00 F7 FF FF FF FB FF 00 00 FB FF 01 00 F5 FF FE FF F7 FF FD FF FA FF FE FF F9 FF 00 00 F7 FF FF FF F8 FF FF FF F9 FF 01 00 F3 FF 00 00 F5 FF FE FF F7 FF FF FF F5 FF FF FF F7 FF 01 00 FD FF 00 00 FA FF FC FF F5 FF F9 FF F3 FF FB FF F2 FF FC FF F3 FF FE FF F9 FF 01 00 FD FF FE FF FE FF FF FF F4 FF FF FF F0 FF FC FF F1 FF FF FF F8 FF 03 00 04 00 04 00 03 00 06 00 FD FF 04 00 F6 FF FC FF F5 FF F8 FF F5 FF F9 FF F9 FF FC FF FD FF 02 00 FB FF 05 00 FA FF
Read sector 62333937 through win32file:
FF FF FD FF 01 00 FC FF 01 00 FA FF FE FF F6 FF 02 00 F5 FF 06 00 F7 FF 03 00 FD FF 00 00 03 00 00 00 00 00 04 00 FA FF 07 00 F9 FF 05 00 F7 FF 00 00 FB FF FC FF FD FF 00 00 FC FF 04 00 FB FF 04 00 FB FF 02 00 FF FF 01 00 F9 FF FE FF F4 FF BF 75 03 00 EB B2 11 00 C0 31 2D 67 00 06 00 00 FF FF F2 FF 02 00 F2 FF 03 00 F7 FF 01 00 FB FF FB FF F4 FF FA FF F4 FF F8 FF ED FF F7 FF E8 FF F5 FF F0 FF F6 FF F4 FF F7 FF F9 FF F9 FF F6 FF FF FF F6 FF FF FF F7 FF FC FF F5 FF FA FF F5 FF F7 FF F6 FF FC FF F4 FF FF FF FA FF FE FF FC FF FC FF FD FF FC FF F8 FF F8 FF F3 FF F6 FF EE FF F3 FF EE FF F6 FF F4 FF F6 FF F6 FF FB FF F7 FF FF FF F8 FF FF FF F6 FF FC FF F5 FF F9 FF F5 FF F8 FF F3 FF F6 FF F4 FF FA FF F7 FF FC FF F8 FF FA FF FC FF FE FF FB FF FC FF F6 FF FA FF F4 FF FB FF F2 FF FA FF F3 FF FE FF F5 FF F9 FF FC FF F8 FF FB FF FA FF F4 FF FC FF F7 FF FF FF F5 FF FB FF F8 FF F9 FF F6 FF F7 FF F6 FF F9 FF F3 FF F9 FF F1 FF FA FF F4 FF FA FF F8 FF F6 FF FA FF F6 FF F4 FF F5 FF F1 FF F9 FF F3 FF FB FF F6 FF F6 FF F6 FF F5 FF F6 FF FC FF F9 FF 00 00 F4 FF FC FF F4 FF FD FF F7 FF FD FF F9 FF 01 00 FA FF FF FF FE FF 00 00 FE FF 01 00 02 00 03 00 03 00 03 00 FE FF 05 00 FF FF 05 00 04 00 09 00 0A 00 0C 00 0F 00 0B 00 10 00 0F 00 0D 00 12 00 09 00 11 00 0A 00 11 00 0B 00 0D 00 12 00 11 00 16 00 15 00 15 00 18 00 19 00 19 00 18 00 14 00 18 00 11 00 16 00 12 00 14 00 13 00 15 00 17 00 1C 00 17 00 20 00 1A 00 1F 00 1D 00 1C 00 1A 00 16 00 16 00 14 00 11 00 11 00 11 00 15 00 14 00 1F 00 19 00 1E 00 1B 00 1C 00 15 00 17 00 17 00 16 00
Read sector 62333937 through open:
Traceback (most recent call last):
  File "...", line 29, in <module>
    result = device.read(DEVICE_SECTOR_SIZ)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
PermissionError: [Errno 13] Permission denied

Note that when I see this, the generated Errno is different for different devices. This could possibly be a bug in some Windows API that Python is relying on, but I'm not the one to determine that. If buffering is disabled in the Python file interface (by adding , 0 to the end of the open(...) call) then this issue does not occur, so my immediate suspicion is that the buffer implementation is reading past the end of the device for some reason.

This has been tested with Python 3.12.3 on Windows 11 10.0.22631

CPython versions tested on:

3.12

Operating systems tested on:

Windows

Start with the provided minimal reproduction on Windows 11 using Python 3.12.3, comparing buffered open(...).read() with buffering disabled and the win32file path. Done means the buffered Python file interface no longer fails when reading the final sectors of the device, with the behavior covered by an appropriate regression test.