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Date: Mon, 22 Jun 2015 14:15:49 -0700
Message-ID: <CAOBROv3gK-1GgBd6DaYK92Vt2L5ZPhymMxDGy-8rB0hGd6=VSg@mail.gmail.com>
Subject: Re: cacls combination problem in 1.7.35, merging privs of existing file & privs of process
From: John Ruckstuhl <john DOT ruckstuhl AT gmail DOT com>
To: cygwin AT cygwin DOT com
Content-Type: text/plain; charset=UTF-8

On Sat, Jun 20, 2015 at 11:41 AM, John Ruckstuhl
<John DOT Ruckstuhl AT intusurg DOT com> wrote:
>
> I'm noticing this summer, that whenever I try to edit an existing file with vi for the first time, the file's permissions change.  Could this be a problem with merging permissions of existing file and permissions of the vi process?

To clarify, for me, when the vi process is writing out a fresh file,
the new file gets an acl ...  Then when vi overwrites that file
(presumably creating a new file with an acl per the merging of the
existing acl and new-file acl, the result is different acl.  The file
when first written -- execution via the shebang works.  When updated,
something -- the file or the shebang -- doesn't execute anymore.

I believe this is easily reproducible (1.7.35).  My umask is 0022.

1.  In vi, create 2 lines of content including a shebang, like this:
        !# /usr/bin/sh
        date
2.  write it out to a file, like try.sh
3.  execute it
        ./try.sh
    it works, right?
4.  write the file back out a 2nd time (no changes)
5.  execute it again
        ./try.sh
    but this time, it doesn't work
        -bash: ./try.sh: Permission denied
6.  now delete the shebang line, and write the file out (3rd time)
7.  execute it again
        ./try.sh
    it works again.  Huh?

So yes I am still puzzled about the acl diff between the 1st & 2nd
file-write, and also it looks like it's a shebang interaction.

FWIW, I think my user sid & group sid are different. See Footnote [3] below.

Best regards,
John

Footnotes
[3]
I claim user sid & group sid are different because id says:
    uid=1158474(johnru) gid=1049089(Domain Users)
groups=1049089(Domain
Users),544(Administrators),545(Users),4(INTERACTIVE),66049(CONSOLE
LOGON),11(Authenticated Users),15(This
Organization),4095(CurrentSession),66048(LOCAL),1058289(Corporate
Employees), ...

and the RIDs are different (109898 != 513) (btw, is this the accepted
technique to get SID?):

    C:\Users\johnru>wmic useraccount where name='JohnRu' get sid
    SID
    S-1-5-21-25853599-488532567-929701000-109898

    C:\Users\johnru>wmic group where name='Domain Users' get sid
    SID
    S-1-5-21-25853599-488532567-929701000-513

>
> Original cacls of file try2.txt:
>     try2.txt INTSURG\johnru:(R,W,D,WDAC,WO)
>              INTSURG\Domain Users:(R)
>              Everyone:(R)
>              NT AUTHORITY\SYSTEM:(F)
>              BUILTIN\Administrators:(F)
> Cacls after vi open & write back out (":wq")
>     try2.txt INTSURG\johnru:(DENY)(S,X)
>              INTSURG\johnru:(R,W,D,WDAC,WO)
>              INTSURG\Domain Users:(RX,W)
>              Everyone:(R)
>              NT AUTHORITY\SYSTEM:(RX,W)
>              BUILTIN\Administrators:(RX,W)
> Note 1 added deny line, and 3 lines changed from (R) or (F), to (RX,W).
>
> Or see differing getfacl output... try1.txt is a fresh file, try2.txt is a file re-written by vi session:
>     johnru AT JohnRu-L1 ~/Desktop/dev NSIS/foul
>     $ getfacl . try*
>     # file: .
>     # owner: johnru
>     # group: Domain Users
>     user::rwx
>     group::r-x
>     group:SYSTEM:rwx
>     group:Administrators:rwx
>     mask:rwx
>     other:r-x
>     default:user::rwx
>     default:group::r-x
>     default:group:SYSTEM:rwx
>     default:group:Administrators:rwx
>     default:mask:rwx
>     default:other:r-x
>
>     # file: try1.txt
>     # owner: johnru
>     # group: Domain Users
>     user::rw-
>     group::r--
>     group:SYSTEM:rwx
>     group:Administrators:rwx
>     mask:rwx
>     other:r--
>
>     # file: try2.txt
>     # owner: johnru
>     # group: Domain Users
>     user::rw-
>     group::rwx
>     group:SYSTEM:rwx
>     group:Administrators:rwx
>     mask:rwx
>     other:r--
>
>
> From the same shell, writing out a file by two techniques yields different cacls.
> Please help me understand the phenomenon.
> I am suspecting vi (or a library it calls) which tries to combine existing privileges of a file with the privs of the vi process, to generate privileges of the new file created on ":w".
> I am not asking for this behavior to be changed, and yes I'm expecting the behavior is different with Cygwin 2.0 .
> I am just trying to understand what is happening here, and which sw app or library is defining this behavior.  Is it vi?  Is it the cygwin1.dll?
> Sorry, I am using the terms privilege, permission, and cacl interchangeably out of ignorance.
> Also, I have tried to read https://cygwin.com/cygwin-ug-net/ntsec.html .  Sorry, I don't see that it documents this phenomenon.  I looked in mailing-list archives, and I couldn't connect the dots.  Again this is 1.7.35 .
> cygcheck.out is attached.
> id.out is attached.
>
> Use case:
> I create a file by redirecting stdout to a file.
> Then I open in vi and write it back out (":wq") and its cacls have changed.  Notably, as you can see, I no longer have "execute" permission.
> Is this a feature of vi, of bash, or of cygwin?
>
> It seems like bash & vi are using different techniques for determining how to specify the cacls of a new file (vi creating a new file on write).
> I know that over the past six months, cygwin handling of acls has been a topic of discussion.
> Also note,
> (a) this is on my C drive, under my Desktop, not on some remote fileserver.
> (b) Windows 7.
> (c) my IT dept routinely gives power-users Window Administrator privileges, so I have that, even though I'm not sure I want that attached to my day-to-day account.
> (d) while I am making these observations, I am at home, not on my domain network.
>
> Below, my control case is try1.txt, and my experiment is try2.txt (see Footnote [1]).
>
> Hmmm what if I write a new file with vi (instead of rewriting a file).
> Ahhh, In the new file case, vi writes file with same cacls as a fresh file written by shell redirect.
> Maybe what I'm observing is vi is trying to respect the original cacls when creating the updated file.
> So it's a problem with vi's attempt to combine the files original cacls with vi's notion of the privileges of its own process... (see Footnote [2])
>
> Footnotes
> [1]
> johnru AT JohnRu-L1 ~/Desktop/dev NSIS/foul
> $ icacls .
> . INTSURG\johnru:(F)
>   INTSURG\Domain Users:(RX)
>   Everyone:(RX)
>   NT AUTHORITY\SYSTEM:(OI)(CI)(F)
>   BUILTIN\Administrators:(OI)(CI)(F)
>   CREATOR OWNER:(OI)(CI)(IO)(F)
>   CREATOR GROUP:(OI)(CI)(IO)(RX)
>   Everyone:(OI)(CI)(IO)(RX)
>
> Successfully processed 1 files; Failed processing 0 files
>
> johnru AT JohnRu-L1 ~/Desktop/dev NSIS/foul
> $ date > try1.txt
>
> johnru AT JohnRu-L1 ~/Desktop/dev NSIS/foul
> $ date > try2.txt
>
> johnru AT JohnRu-L1 ~/Desktop/dev NSIS/foul
> $ icacls try1.txt; icacls try2.txt
> try1.txt INTSURG\johnru:(R,W,D,WDAC,WO)
>          INTSURG\Domain Users:(R)
>          Everyone:(R)
>          NT AUTHORITY\SYSTEM:(F)
>          BUILTIN\Administrators:(F)
>
> Successfully processed 1 files; Failed processing 0 files
> try2.txt INTSURG\johnru:(R,W,D,WDAC,WO)
>          INTSURG\Domain Users:(R)
>          Everyone:(R)
>          NT AUTHORITY\SYSTEM:(F)
>          BUILTIN\Administrators:(F)
>
> Successfully processed 1 files; Failed processing 0 files
>
> (now edit file "try2.txt", and write it back out ":wq")
> johnru AT JohnRu-L1 ~/Desktop/dev NSIS/foul
> $ vi try2.txt
>
> (cacls have been changed! )
> johnru AT JohnRu-L1 ~/Desktop/dev NSIS/foul
> $ icacls try1.txt; icacls try2.txt
> try1.txt INTSURG\johnru:(R,W,D,WDAC,WO)
>          INTSURG\Domain Users:(R)
>          Everyone:(R)
>          NT AUTHORITY\SYSTEM:(F)
>          BUILTIN\Administrators:(F)
>
> Successfully processed 1 files; Failed processing 0 files
> try2.txt INTSURG\johnru:(DENY)(S,X)
>          INTSURG\johnru:(R,W,D,WDAC,WO)
>          INTSURG\Domain Users:(RX,W)
>          Everyone:(R)
>          NT AUTHORITY\SYSTEM:(RX,W)
>          BUILTIN\Administrators:(RX,W)
>
> Successfully processed 1 files; Failed processing 0 files
>
> johnru AT JohnRu-L1 ~/Desktop/dev NSIS/foul
> $ ls -la
> total 6
> drwxrwxr-x+ 1 johnru         Domain Users  0 Jun 20 09:34 .
> drwxrwx---+ 1 Administrators Domain Users  0 Jun 20 09:32 ..
> -rw-rwxr--+ 1 johnru         Domain Users 30 Jun 20 09:33 try1.txt
> -rw-rwxr--+ 1 johnru         Domain Users 30 Jun 20 09:34 try2.txt
>
>
> [2] file "try3.txt" doesn't exist yet.  Using vi to create it with the following command
> johnru AT JohnRu-L1 ~/Desktop/dev NSIS/foul
> $ vi try3.txt
>
> johnru AT JohnRu-L1 ~/Desktop/dev NSIS/foul
> $ icacls try3.txt
> try3.txt INTSURG\johnru:(R,W,D,WDAC,WO)
>          INTSURG\Domain Users:(R)
>          Everyone:(R)
>          NT AUTHORITY\SYSTEM:(F)
>          BUILTIN\Administrators:(F)
>
> Successfully processed 1 files; Failed processing 0 files
>
> johnru AT JohnRu-L1 ~/Desktop/dev NSIS/foul
> $ icacls try3.txt
> try3.txt INTSURG\johnru:(R,W,D,WDAC,WO)
>          INTSURG\Domain Users:(R)
>          Everyone:(R)
>          NT AUTHORITY\SYSTEM:(F)
>          BUILTIN\Administrators:(F)
>
> Successfully processed 1 files; Failed processing 0 files
>
> johnru AT JohnRu-L1 ~/Desktop/dev NSIS/foul
> $ vi try3.txt
>
> johnru AT JohnRu-L1 ~/Desktop/dev NSIS/foul
> $ icacls try3.txt
> try3.txt INTSURG\johnru:(DENY)(S,X)
>          INTSURG\johnru:(R,W,D,WDAC,WO)
>          INTSURG\Domain Users:(RX,W)
>          Everyone:(R)
>          NT AUTHORITY\SYSTEM:(RX,W)
>          BUILTIN\Administrators:(RX,W)
>
> Successfully processed 1 files; Failed processing 0 files
>
>
>
>
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