Problems with native Unix domain sockets on Win 10/2019

[Michael McMahon]

On 30/01/2021 16:00, Ken Brown wrote:
> On 9/28/2020 7:03 AM, Michael McMahon wrote:
>>
>>
>> On 26/09/2020 08:30, Michael McMahon via Cygwin wrote:
>>>
>>>
>>> On 25/09/2020 21:30, Ken Brown wrote:
>>>> On 9/25/2020 2:50 PM, Ken Brown via Cygwin wrote:
>>>>> On 9/25/2020 10:29 AM, Michael McMahon wrote:
>>>>>>
>>>>>>
>>>>>> On 25/09/2020 14:19, Ken Brown wrote:
>>>>>>> On 9/24/2020 8:01 AM, Michael McMahon wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>> On 24/09/2020 12:26, Ken Brown wrote:
>>>>>>>>> On 9/23/2020 7:25 AM, Michael McMahon via Cygwin wrote:
>>>>>>>>>> Hi,
>>>>>>>>>>
>>>>>>>>>> I searched for related issues but haven't found anything.
>>>>>>>>>>
>>>>>>>>>> I am having some trouble with Windows native Unix domain
>>>>>>>>>> sockets (a recent feature in Windows 10 and 2019 server) and
>>>>>>>>>> Cygwin. I think I possibly know the cause since I had to
>>>>>>>>>> investigate a similar looking issue on another platform built
>>>>>>>>>> on Windows.
>>>>>>>>>>
>>>>>>>>>> The problem is that cygwin commands don't seem to recognise
>>>>>>>>>> native Unix domain sockets correctly. For example, the socket
>>>>>>>>>> "foo.sock" should have the same ownership and similar
>>>>>>>>>> permissions to other files in the example below:
>>>>>>>>>>
>>>>>>>>>> $ ls -lrt total 2181303
>>>>>>>>>>
>>>>>>>>>> -rw-r--r--  1 mimcmah      None 1259   Sep 23
>>>>>>>>>> 10:22 test.c -rwxr-xr-x  1 mimcmah None             3680
>>>>>>>>>> Sep 23 10:22 test.obj -rwxr-xr-x  1 mimcmah None
>>>>>>>>>> 121344 Sep 23 10:22 test.exe -rw-r-----  1 Unknown+User
>>>>>>>>>> Unknown+Group         0 Sep 23 10:23 foo.sock -rw-r--r--  1
>>>>>>>>>> mimcmah      None             144356 Sep 23 10:27 check.ot
>>>>>>>>>>
>>>>>>>>>> A bigger problem is that foo.sock can't be deleted with the
>>>>>>>>>> cygwin "rm" command.
>>>>>>>>>>
>>>>>>>>>> $ rm -f foo.sock rm: cannot remove 'foo.sock': Permission
>>>>>>>>>> denied
>>>>>>>>>>
>>>>>>>>>> $ chmod 777 foo.sock chmod: changing permissions of
>>>>>>>>>> 'foo.sock': Permission denied
>>>>>>>>>>
>>>>>>>>>> $ cmd /c del foo.sock
>>>>>>>>>>
>>>>>>>>>> But, native Windows commands are okay, as the third example
>>>>>>>>>> shows.
>>>>>>>>>>
>>>>>>>>>> I think the problem may relate to the way native Unix domain
>>>>>>>>>> sockets are implemented in Windows and the resulting special
>>>>>>>>>> handling required. They are implemented as NTFS reparse
>>>>>>>>>> points and when opening them with CreateFile, you need to
>>>>>>>>>> specify the FILE_FLAG_OPEN_REPARSE_POINT flag. Otherwise, you
>>>>>>>>>> get an ERROR_CANT_ACCESS_FILE. There are other complications
>>>>>>>>>> unfortunately, which I'd be happy to discuss further.
>>>>>>>>>>
>>>>>>>>>> But, to reproduce it, you can compile the attached code
>>>>>>>>>> snippet which creates foo.sock in the current directory.
>>>>>>>>>> Obviously, this only works on recent versions of Windows 10
>>>>>>>>>> and 2019 server.
>>>>>>>>>
>>>>>>>>> Cygwin doesn't currently support native Windows AF_UNIX
>>>>>>>>> sockets, as you've discovered.  See
>>>>>>>>>
>>>>>>>>> https://urldefense.com/v3/__https://cygwin.com/pipermail/cygwin/2020-June/245088.html__;!!GqivPVa7Brio!P7lIFI4rYAtWh8_DtCbRCxT-M_E4vwQ0qwzQ0p656T73BpJ0jbUkLI_bXdA6mmSL9lJcSQ$ 
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> for the current state of AF_UNIX sockets on Cygwin, including
>>>>>>>>> the possibility of using native Windows AF_UNIX sockets on
>>>>>>>>> systems that support them.
>>>>>>>>>
>>>>>>>>> If all you want is for Cygwin to recognize such sockets and
>>>>>>>>> allow you to apply rm, chmod, etc., I don't think it would be
>>>>>>>>> hard to add that capability.  But I doubt if that's all you
>>>>>>>>> want.
>>>>>>>>>
>>>>>>>>> Further discussion of this will have to wait until Corinna is
>>>>>>>>> available.
>>>>>>>>>
>>>>>>>>
>>>>>>>> Thanks for the info. It's mainly about recognition of sockets
>>>>>>>> for regular commands. Since these objects can exist on Windows
>>>>>>>> filesystems now, potentially created by any kind of Windows
>>>>>>>> application, it would be great if Cygwin could handle them,
>>>>>>>> irrespective of whether the Cygwin development environment does.
>>>>>>>> Though that sounds like a good idea too.
>>>>>>>
>>>>>>> I think this has a simple fix (attached), but I can't easily test
>>>>>>> it because your test program doesn't compile for me. First, I got
>>>>>>>
>>>>>>> $ gcc -o native_unix_socket native_unix_socket.c 
>>>>>>> native_unix_socket.c:5:10: fatal error: WS2tcpip.h: No such file or
>>>>>>> directory 5 | #include <WS2tcpip.h> | ^~~~~~~~~~~~ compilation 
>>>>>>> terminated.
>>>>>>>
>>>>>>> I fixed this by making the include file name lower case.  (My
>>>>>>> system is case sensitive, so it matters.)
>>>>>>>
>>>>>>> Next:
>>>>>>>
>>>>>>> $ gcc -o native_unix_socket native_unix_socket.c 
>>>>>>> native_unix_socket.c:8:10: fatal error: afunix.h: No such file or
>>>>>>> directory 8 | #include <afunix.h> | ^~~~~~~~~~ compilation
>>>>>>> terminated.
>>>>>>>
>>>>>>> There's no file afunix.h in the Cygwin distribution, but I located
>>>>>>> it online and pasted in the contents.  The program now compiles but
>>>>>>> fails to link:
>>>>>>>
>>>>>>> $ gcc -o native_unix_socket native_unix_socket.c 
>>>>>>> /usr/lib/gcc/x86_64-pc-cygwin/10/../../../../x86_64-pc-cygwin/bin/ld: 
>>>>>>>
>>>>>>>  /tmp/cc74urPr.o:native_unix_socket.c:(.text+0x3b): undefined
>>>>>>> reference to `__imp_WSAStartup' 
>>>>>>> /tmp/cc74urPr.o:native_unix_socket.c:(.text+0x3b): relocation
>>>>>>> truncated to fit: R_X86_64_PC32 against undefined symbol
>>>>>>> `__imp_WSAStartup' 
>>>>>>> /usr/lib/gcc/x86_64-pc-cygwin/10/../../../../x86_64-pc-cygwin/bin/ld: 
>>>>>>>
>>>>>>>  /tmp/cc74urPr.o:native_unix_socket.c:(.text+0xf2): undefined
>>>>>>> reference to `__imp_WSAGetLastError' 
>>>>>>> /tmp/cc74urPr.o:native_unix_socket.c:(.text+0xf2): relocation
>>>>>>> truncated to fit: R_X86_64_PC32 against undefined symbol
>>>>>>> `__imp_WSAGetLastError' 
>>>>>>> /usr/lib/gcc/x86_64-pc-cygwin/10/../../../../x86_64-pc-cygwin/bin/ld: 
>>>>>>>
>>>>>>>  /tmp/cc74urPr.o:native_unix_socket.c:(.text+0x13d): undefined
>>>>>>> reference to `__imp_WSAGetLastError' 
>>>>>>> /tmp/cc74urPr.o:native_unix_socket.c:(.text+0x13d): relocation
>>>>>>> truncated to fit: R_X86_64_PC32 against undefined symbol
>>>>>>> `__imp_WSAGetLastError' collect2: error: ld returned 1 exit status
>>>>>>>
>>>>>>> This is probably easy to fix too, but I don't feel like tracking it
>>>>>>> down. Please send compilation instructions (that use Cygwin
>>>>>>> tools).
>>>>>>>
>>>>>>> Ken
>>>>>>
>>>>>> Hi
>>>>>>
>>>>>> Sorry, I had compiled it in a native Visual C environment.
>>>>>>
>>>>>> Assuming you have afunix.h in the current directory.
>>>>>>
>>>>>> gcc -o native_unix_socket -I. native_unix_socket.c -lws2_32
>>>>>>
>>>>>> should do it.
>>>>>
>>>>> Thanks, that works.  But now I can't reproduce your problem.  Here's
>>>>> what I see, using Cygwin 3.1.7 without applying my patch:
>>>>>
>>>>> $ ./native_unix_socket.exe getsockname works fam = 1, len = 11 
>>>>> offsetof
>>>>> clen = 9 strlen = 8 name = foo.sock
>>>>>
>>>>> $ ls -l foo.sock -rwxr-xr-x 1 kbrown None 0 2020-09-25 14:39 
>>>>> foo.sock*
>>>>>
>>>>> $ chmod 644 foo.sock
>>>>>
>>>>> $ ls -l foo.sock -rw-r--r-- 1 kbrown None 0 2020-09-25 14:39 foo.sock
>>>>>
>>>>> $ rm foo.sock
>>>>>
>>>>> $ ls -l foo.sock ls: cannot access 'foo.sock': No such file or
>>>>> directory
>>>>>
>>>>> I'm running 64-bit Cygwin on Windows 10 1909.
>>>>
>>>> I just ran the 'rm' command under gdb to see what's going on, and it
>>>> seems that foo.sock is not being recognized as a reparse point.  So 
>>>> maybe
>>>> your test program, when compiled and run under Cygwin, doesn't 
>>>> actually
>>>> produce a native Windows AF_UNIX socket.  And when I try to run it 
>>>> in a
>>>> Windows Command Prompt, I get
>>>>
>>>> bind failed 10050 getsockname failed 10022
>>>>
>>>> Can you make your version of the test executable available for me 
>>>> to try?
>>>> Or tell me some other way to create a native Windows AF_UNIX socket?
>>>>
>>>> Ken
>>>
>>> That is all very strange. I have checked both the gcc compiled and 
>>> MS compiled executables on my system (2019 server) and they are both 
>>> definitely producing native AF_UNIX sockets.
>>>
>>> I can email you the two exe files. They are both quite small. But, 
>>> first I
>>> want to check the patch status of my test system.
>>>
>>
>> So, it turns out that this issue only happens on some of our test 
>> systems. It
>> does not happen on a personal copy of Windows 10 on my laptop either.
>>
>> I also noticed that some native Windows commands don't work properly 
>> on any
>> affected system (eg 'attrib' or 'fsutil'). Though 'fsutil' can be 
>> used to
>> verify that the reparse point is created correctly.
>>
>> Possibly, this was a Windows bug that has been fixed. It never made 
>> sense
>> that you had to open socket files using the 
>> FILE_FLAG_OPEN_REPARSE_POINT flag, because you would have to know in 
>> advance that the file is a socket to
>> be able to do this (or else be prepared to have to open the file 
>> twice). But,
>> I don't fully understand yet, why some systems are affected and 
>> others not. All seem to be patched up to date.
>>
>> In any case, I think it's clear this isn't a Cygwin issue.
>
> It turns out that this is a Cygwin issue after all.  In a private message
> Michael has said:
>
>> From what I can see, the only versions that are *not* affected by the 
>> problem
>> are 1903 and 1909 (which you tested with).  Versions I have tested 
>> with since
>> then (2004, and 20H2) all show the problem.
>
> I can't immediately test it myself because I'm still on 1909.  But 
> I'll send a patch to cygwin-patches that I think should fix it, along 
> with Michael's test program.
>
> Ken

Thanks for taking this up again. While I had thought it was a Windows 
bug, and it is arguable, but at least there is a reasonable workaround 
for it. I'd be happy to test an update you have for it.

Michael.