Re: Weird problem with long $PATH and alternates (bisected)

[Junio C Hamano <gitster@pobox.com>]

René Scharfe <rene.scharfe@lsrfire.ath.cx> writes:

> Junio C Hamano schrieb:
>> "Mikael Magnusson" <mikachu@gmail.com> writes:
>> 
>>> % mkdir 1; cd 1
>>> % echo > a; git add a; git commit -m a
>>> % cd ..
>>> % git clone -s 1 2
>>> % git push . master:master
>>> fatal: Could not switch to
>>> '/tmp/a/1/.git/objects/n:/usr/games/bin:/usr/local/ipod-chain'
>>> fatal: The remote end hung up unexpectedly
>> 
>> I think I see a bug in foreach_alt_odb() to add_refs_from_alternate()
>> callchain, but I cannot explain why the contents of $PATH leaks to the
>> error message.
>
> With the following patch, I can no longer reproduce the problem.  Does it
> work fo you, too?
>
> Thanks,
> René
>
> diff --git a/sha1_file.c b/sha1_file.c
> index ab2b520..8044e9c 100644
> --- a/sha1_file.c
> +++ b/sha1_file.c
> @@ -269,7 +269,7 @@ static int link_alt_odb_entry(const char * entry, int len, const char * relative
>  		entlen += base_len;
>  		pfxlen += base_len;
>  	}
> -	ent = xmalloc(sizeof(*ent) + entlen);
> +	ent = xcalloc(1, sizeof(*ent) + entlen);

Ah, that would explain the "filled with garbage from $PATH" issue, but I
don't think it fixes the fundamental issue.

In the alternate_object_database structure, ent->base[] is a buffer the
users can use to form pathnames to loose objects, and ent->name is a
pointer into that buffer (it points at one beyond ".git/objects/").  If
you get a call to add_refs_from_alternate() after somebody used the entry
(has_loose_object() has been called, for example), *ent->name would not be
NUL, and ent->base[] won't be the path to the object store.

This caller is expecting to read the path to the object store in ent->base[];
it needs to NUL terminate the buffer if it wants to.

I think the previous patch to sha1_file.c, while it may fix the issue, is
not quite nice.  Here is a replacement that should work.

 builtin-receive-pack.c |    9 +++++++--
 1 files changed, 7 insertions(+), 2 deletions(-)

diff --git c/builtin-receive-pack.c w/builtin-receive-pack.c
index 45e3cd9..9f60f31 100644
--- c/builtin-receive-pack.c
+++ w/builtin-receive-pack.c
@@ -466,12 +466,17 @@ static int delete_only(struct command *cmd)
 
 static int add_refs_from_alternate(struct alternate_object_database *e, void *unused)
 {
-	char *other = xstrdup(make_absolute_path(e->base));
-	size_t len = strlen(other);
+	char *other;
+	size_t len;
 	struct remote *remote;
 	struct transport *transport;
 	const struct ref *extra;
 
+	e->name[-1] = '\0';
+	other = xstrdup(make_absolute_path(e->base));
+	e->name[-1] = '/';
+	len = strlen(other);
+
 	while (other[len-1] == '/')
 		other[--len] = '\0';
 	if (len < 8 || memcmp(other + len - 8, "/objects", 8))