Bug encountered while comitting

Bug encountered while comitting

[Matthias Kestenholz]

Hello list,

I don't know if this is the right place to report a bug, but I'll
just try and see what comes back.

I am trying to build a Wiki [1] using PHP, a hacked version of Markdown,
and git for content tracking. I use the git core plumbing to do the
history work.

The PHP script created directories under .git/objects which were
only writable by www-data. There were other directories which were
owned by user mk and group www-data, and they were group writable.

So, I had write access to only a part of the .git directory.

When I tried to commit, I got a message saying "Unable to write sha1
filename".

The result was, that only part of the commit was recorded and that I
experienced repository corruption. refs/heads/master pointed to a
non-existant object.

The expected behavior would have been an error message telling me I
had insufficient write privileges and surely no repository
corruption.



Thanks,
Matthias


[1]: http://spinlock.ch/cgi-bin/gitweb.pl?p=swisdk2/bugs.git;a=tree
(See Wiki_ctrl.php for source)


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Re: Bug encountered while comitting

[Andreas Ericsson]

Matthias Kestenholz wrote:
> Hello list,
> 
> I don't know if this is the right place to report a bug, but I'll
> just try and see what comes back.
> 
> I am trying to build a Wiki [1] using PHP, a hacked version of Markdown,
> and git for content tracking. I use the git core plumbing to do the
> history work.
> 
> The PHP script created directories under .git/objects


Ouch... You're not really supposed to do that. The proper thing to do is 
to do things in the working tree and commit them to git later.


> which were
> only writable by www-data. There were other directories which were
> owned by user mk and group www-data, and they were group writable.
> 
> So, I had write access to only a part of the .git directory.
> 

Unless you're using the git tools (or things hooking in to the git core 
C functions somehow), don't touch the .git directory.

(this merits an exclamation marks, so brace yourselves) !


> When I tried to commit, I got a message saying "Unable to write sha1
> filename".
> 

What file were you trying to write?

> The result was, that only part of the commit was recorded and that I
> experienced repository corruption. refs/heads/master pointed to a
> non-existant object.
> 

Did you use git tools to update .git/refs/heads/master ?


> The expected behavior would have been an error message telling me I
> had insufficient write privileges and surely no repository
> corruption.
> 

Didn't you get the strerror(3) message from that? If so, I'd consider it 
a bug.

-- 
Andreas Ericsson                   andreas.ericsson@op5.se
OP5 AB                             www.op5.se
Tel: +46 8-230225                  Fax: +46 8-230231

Re: Bug encountered while comitting

[Matthias Kestenholz]

* Andreas Ericsson (ae@op5.se) wrote:
> Matthias Kestenholz wrote:
> >
> >The PHP script created directories under .git/objects
> 
> 
> Ouch... You're not really supposed to do that. The proper thing to do is 
> to do things in the working tree and commit them to git later.
> 

I think I did not express myself clearly. The PHP Script executes
git commands which in turn create or modify the mentioned
directories. I do not create them myself by hand.

> >When I tried to commit, I got a message saying "Unable to write sha1
> >filename".
> >
> 
> What file were you trying to write?
> 

Some file I was updating (in this case, a file holding some wiki
content)

> >The result was, that only part of the commit was recorded and that I
> >experienced repository corruption. refs/heads/master pointed to a
> >non-existant object.
> >
> 
> Did you use git tools to update .git/refs/heads/master ?
> 

Yes.

> 
> >The expected behavior would have been an error message telling me I
> >had insufficient write privileges and surely no repository
> >corruption.
> >
> 
> Didn't you get the strerror(3) message from that? If so, I'd consider it 
> a bug.

As I (only now) wrote in the other email, I got the
"Permission denied" message, and that was a sufficient hint what was
wrong.

-- 
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Re: Bug encountered while comitting

[Junio C Hamano]

Matthias Kestenholz <lists@irregular.ch> writes:

> The PHP script created directories under .git/objects which were
> only writable by www-data. There were other directories which were
> owned by user mk and group www-data, and they were group writable.
>
> So, I had write access to only a part of the .git directory.

core.sharedrepository perhaps?

While it probably is not a good idea to have you in www-data, it
appears that is essentially you will end up doing, because PHP
scripts that may _create_ new directories better not to have
privilege to give newly created directories away to you (busting
your quota), so they will be owned by www-data.www-data and for
you to be able to write into it you either need to be www-data
user or in www-data group, with core.sharedrepostiory set.

Re: Bug encountered while comitting

[Matthias Kestenholz]

* Junio C Hamano (junkio@cox.net) wrote:
> Matthias Kestenholz <lists@irregular.ch> writes:
> 
> > The PHP script created directories under .git/objects which were
> > only writable by www-data. There were other directories which were
> > owned by user mk and group www-data, and they were group writable.
> >
> > So, I had write access to only a part of the .git directory.
> 
> core.sharedrepository perhaps?
> 
> While it probably is not a good idea to have you in www-data, it
> appears that is essentially you will end up doing, because PHP
> scripts that may _create_ new directories better not to have
> privilege to give newly created directories away to you (busting
> your quota), so they will be owned by www-data.www-data and for
> you to be able to write into it you either need to be www-data
> user or in www-data group, with core.sharedrepostiory set.
> 

Thanks for your answer; I did not know about this option (I should
probably re-read all the docs).

Anyway, I think git should never corrupt a repository, even if it
does not have the write permissions it needs.

The following commands were sufficient to create a corrupt
repository with git (v1.2.4-1, debian package):

$ git-init-db
$ echo test > file
$ git-update-index --add file ; git commit -m 'message'

repeat (f.e. 10 times):
$ echo test >> file
$ git-update-index file ; git commit -m 'message'

$ sudo chown root .git/objects/*

repeat the modification and commit commands until you get a message
similar to the following:

unable to write sha1 filename .git/objects/90/b33..: Permission denied
fatal: 90b33... is not a valid 'tree' object
unable to write sha1 filename .git/objects/ba/fe4..: Permission denied
error: file: failed to insert into database
fatal: Unable to process file file
etc...

The result of this all is: refs/heads/master might now point to a
non-existant commit object. Every git command now errors out with:

fatal: bad tree object HEAD

and git-log shows no output (probably since it does not find a
commit to begin with)


git-commit should abort as soon as it encounters an error and not
update HEAD.

Thanks,
Matthias

(Note: To find the last valid commit object, I could just scan the
objects directory for the recently modified files and write the sha1
value to refs/heads/master, so I had no data loss.)



-- 
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Re: Bug encountered while comitting

[Junio C Hamano]

Matthias Kestenholz <lists@irregular.ch> writes:

> $ sudo chown root .git/objects/*
>
> repeat the modification and commit commands until you get a message
> similar to the following:
>
> unable to write sha1 filename .git/objects/90/b33..: Permission denied
> fatal: 90b33... is not a valid 'tree' object
> unable to write sha1 filename .git/objects/ba/fe4..: Permission denied
> error: file: failed to insert into database
> fatal: Unable to process file file
> etc...
>
> The result of this all is: refs/heads/master might now point to a
> non-existant commit object. Every git command now errors out with:
>
> fatal: bad tree object HEAD
>
> and git-log shows no output (probably since it does not find a
> commit to begin with)

You are right.  commit-tree does not seem to check if it
successfully wrote the commit object.  How about this?

-- >8 --
diff --git a/commit-tree.c b/commit-tree.c
index 88871b0..16c1787 100644
--- a/commit-tree.c
+++ b/commit-tree.c
@@ -125,7 +125,10 @@ int main(int argc, char **argv)
 	while (fgets(comment, sizeof(comment), stdin) != NULL)
 		add_buffer(&buffer, &size, "%s", comment);
 
-	write_sha1_file(buffer, size, "commit", commit_sha1);
-	printf("%s\n", sha1_to_hex(commit_sha1));
-	return 0;
+	if (!write_sha1_file(buffer, size, "commit", commit_sha1)) {
+		printf("%s\n", sha1_to_hex(commit_sha1));
+		return 0;
+	}
+	else
+		return 1;
 }

Re: Bug encountered while comitting

[Matthias Kestenholz]

* Junio C Hamano (junkio@cox.net) wrote:
> You are right.  commit-tree does not seem to check if it
> successfully wrote the commit object.  How about this?
> 
> -- >8 --
> diff --git a/commit-tree.c b/commit-tree.c
> index 88871b0..16c1787 100644
> --- a/commit-tree.c
> +++ b/commit-tree.c
> @@ -125,7 +125,10 @@ int main(int argc, char **argv)
>  	while (fgets(comment, sizeof(comment), stdin) != NULL)
>  		add_buffer(&buffer, &size, "%s", comment);
>  
> -	write_sha1_file(buffer, size, "commit", commit_sha1);
> -	printf("%s\n", sha1_to_hex(commit_sha1));
> -	return 0;
> +	if (!write_sha1_file(buffer, size, "commit", commit_sha1)) {
> +		printf("%s\n", sha1_to_hex(commit_sha1));
> +		return 0;
> +	}
> +	else
> +		return 1;
>  }

This patch fixes the problem I was encountering (git-update-ref is
not executed anymore).

Thank you all for this really great tool!


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