Re: init --shared=0666 isn't

Steve Folly [off-list ref] writes:

$ git --git-dir=/tmp/shared.git fetch origin

error: cannot open /tmp/shared.git/FETCH_HEAD: Permission denied

FETCH_HEAD is owned by the original user, with 0644 permissions,

The shared repository support was [*1*] designed to help people setting up
a "shared" repository like CVS/SVN, a central place people meet and
exchange their histories by pushing into it and fetching from it.  It was
never designed to be used with a repository with a working tree, hence it
was never designed to be used in repositories you would run "git pull" or
"git merge" in.

However, it is not implausible for a sane workflow that you have to fetch
into a central meeting place.  You might be setting up a shared repository
that also serves as a redistribution center for an external source, and in
such a set-up, you would

 (1) clone/fetch from external "upstream";
 (2) allow people to fetch from it;
 (3) allow people to push into it.

So in that sense, allowing "git fetch" in such a shared central meeting
place is not something we would want to actively forbid.  But I thought we
unlinked existing FETCH_HEAD and then opened to create it anew, so I am a
bit puzzled why it matters who owns it and who can write into it.

    ... goes and looks ...

Ah, truncate_fetch_head() just opens it without unlinking.  Probably a
better fix might be to unlink and create the file, like the attached patch
does, instead of running adjust_shared_perm().

But, I wonder if there are other files written that will need fixing
also - ORIG_HEAD, MERGE_HEAD?

These are created by "merge" and "reset", so it shouldn't matter.

By the way, the same applies to files in the working tree.  We never call
adjust_shared_perm() when creating them, and I do not think this is likely
to change.


[Footnote]

*1* Notice the past tense---this is merely a statement of historical fact
to help you understand _why_ the current system behaves that way and the
conclusion does not necessarily have to be "hence it must remain that
way".

diff --git a/builtin-fetch.c b/builtin-fetch.c
index b6c5b34..d73fa19 100644
--- a/builtin-fetch.c
+++ b/builtin-fetch.c

@@ -654,8 +654,11 @@ static void check_not_current_branch(struct ref *ref_map)
 static int truncate_fetch_head(void)
 {
 	char *filename = git_path("FETCH_HEAD");
-	FILE *fp = fopen(filename, "w");
+	FILE *fp;
 
+	if (unlink(filename) && errno != ENOENT)
+		return error("cannot unlink %s\n", filename);
+	fp = fopen(filename, "w");
 	if (!fp)
 		return error("cannot open %s: %s\n", filename, strerror(errno));
 	fclose(fp);