Re: [PATCH 07/18] link_alt_odb_entry: handle normalize_path errors

["René Scharfe" <l.s.r@web.de>]

Am 03.10.2016 um 22:34 schrieb Jeff King:
> When we add a new alternate to the list, we try to normalize
> out any redundant "..", etc. However, we do not look at the
> return value of normalize_path_copy(), and will happily
> continue with a path that could not be normalized. Worse,
> the normalizing process is done in-place, so we are left
> with whatever half-finished working state the normalizing
> function was in.
>
> Fortunately, this cannot cause us to read past the end of
> our buffer, as that working state will always leave the
> NUL from the original path in place. And we do tend to
> notice problems when we check is_directory() on the path.
> But you can see the nonsense that we feed to is_directory
> with an entry like:
>
>   this/../../is/../../way/../../too/../../deep/../../to/../../resolve
>
> in your objects/info/alternates, which yields:
>
>   error: object directory
>   /to/e/deep/too/way//ects/this/../../is/../../way/../../too/../../deep/../../to/../../resolve
>   does not exist; check .git/objects/info/alternates.
>
> We can easily fix this just by checking the return value.
> But that makes it hard to generate a good error message,
> since we're normalizing in-place and our input value has
> been overwritten by cruft.
>
> Instead, let's provide a strbuf helper that does an in-place
> normalize, but restores the original contents on error. This
> uses a second buffer under the hood, which is slightly less
> efficient, but this is not a performance-critical code path.

Hmm, in-place functions are quite rare in the strbuf collection.  It 
looks like a good fit for the two callers and makes sense in general, 
though.