Re: odb_mkstemp's 0444 permission broke write/delete access on AFP

From: Fairuzan Roslan <fairuzan.roslan@gmail.com>
Date: Feb 17, 2015, 16:58 UTC
Message-ID: <CA0F915F-74B1-4292-AFB8-D1A4C76C0137@gmail.com>
In-Reply-To: <vpqr3tozzs5.fsf@anie.imag.fr>

Show 56 quoted lines

> On Feb 17, 2015, at 4:51 PM, Matthieu Moy <Matthieu.Moy@grenoble-inp.fr> wrote:
> 
> Fairuzan Roslan <fairuzan.roslan@gmail.com> writes:
> 
>> $ git clone https://github.com/robbyrussell/oh-my-zsh.git
>> Cloning into 'oh-my-zsh'...
>> remote: Counting objects: 11830, done.
>> remote: Total 11830 (delta 0), reused 0 (delta 0)
>> Receiving objects: 100% (11830/11830), 2.12 MiB | 481.00 KiB/s, done.
>> Resolving deltas: 100% (6510/6510), done.
>> warning: unable to unlink /Volumes/installer/oh-my-zsh/.git/objects/pack/tmp_pack_zjPxuc: Operation not permitted
> 
> This should be fixable from Git itself, by replacing the calls to
> "unlink" with something like
> 
> int unlink_or_chmod(...) {
> 	if (unlink(...)) {
> 		chmod(...); // give user write permission
> 		return unlink(...);
> 	}
> }
> 
> This does not add extra cost in the normal case, and would fix this
> particular issue for afp shares. So, I think that would fix the biggest
> problem for afp-share users without disturbing others. It seems
> reasonable to me to do that unconditionnally.
> 
>> $ rm -rf oh-my-zsh/.git/objects/pack/tmp_*
>> rm: oh-my-zsh/.git/objects/pack/tmp_idx_oUN1sb: Operation not permitted
>> rm: oh-my-zsh/.git/objects/pack/tmp_pack_zjPxuc: Operation not permitted
> 
> What happens if you do "rm -fr oh-my-zsh/.git/objects/pack/" (i.e.
> remove the directory, not the files)?
> 
> If you can still remove the directory, then I'd say the solution above
> could be sufficient: the user isn't supposed to interfer with the
> content of .git/objects other than by using Git, and if he or she does,
> then asking a chmod prior to an rm seems reasonable.
> 
> If you can't, then it's another problematic use-case (basically, you
> can't just "rm -fr" a whole clone), and then it deserves at least an
> opt-in configuration to get writable pack files.
> 
> (Unfortunately, I suspect we're in the later case)
> 
>> If you insist on setting the tmp idx & pack file permission to 0444 at
>> least give it a u+w permission whenever you try to unlink and rename
>> it so it won’t fail.
> 
> Yes. In case you hadn't guessed, this is precisely what I had in mind
> when I asked "Is it a problem when using Git [...] or when trying to
> remove files outside Git?".
> 
> --
> Matthieu Moy
> http://www-verimag.imag.fr/~moy/

Yes. It’s a problem when using Git where it fails to unlink and rename the tmp idx and pack files. The reason I tries to rm -rf the tmp_idx_XXXXXX and tmp_pack_XXXXXX is to proof a point why Git fails

Perhaps my explanation wasn’t clear enough. Maybe it’s hard for you to understand without having to test it yourself on a AFP filesystem.

Let me explain why AFP filesystem is more strict and different from your typical filesystem like ext4,hfs+,etc.

$ mkdir testdir; chmod 0755 testdir; touch testdir/testfile; chmod 0444 testdir/testfile; ls -la testdir total 0 drwxr-xr-x 1 user staff 264 Feb 18 00:26 . drwx------ 1 user staff 264 Feb 18 00:26 .. -r--r--r-- 1 user staff 0 Feb 18 00:26 testfile

$ rm -rf testdir rm: testdir/testfile: Operation not permitted rm: testdir: Directory not empty

$ chmod +w testdir/testfile; ls -la testdir total 0 drwxr-xr-x 1 riaf staff 264 Feb 18 00:26 . drwx------ 1 riaf staff 264 Feb 18 00:26 .. -rw-r—r-- 1 riaf staff 0 Feb 18 00:26 testfile

$ rm -rf testdir <—— No error message

This show that you cannot delete a directory or a file without a write permission in AFP filesystem.

The problem with Git failing is not because its inability to delete a directory but its inability to unlink and rename tmp_idx_XXXXXX and tmp_pack_XXXXXX because those files were set to 0444 by odb_mkstemp. Try google for “Git AFP” and you will see a lot people are facing with the same problem.

Regarding your suggestion, yes I think it would work but you have to take care (chmod) every calls that rename or unlink or delete files with 0444 permission.

Regards, Fairuzan