From: Junio C Hamano <gitster@pobox.com>
Date: Thu, 16 Feb 2023 17:36:20 GMT
Subject: Re: [PATCH] delta-islands: fix segfault when freeing island marks
Message-ID: <xmqqfsb5qzqj.fsf@gitster.g>
In-Reply-To: <61e490595b80b34c55fd640e093e021ff6fa9591.1676542973.git.ps@pks.im>

Patrick Steinhardt <ps@pks.im> writes:

> In 647982bb71 (delta-islands: free island_marks and bitmaps, 2023-02-03)
> we have introduced logic to free `island_marks` in order to reduce heap
> memory usage in git-pack-objects(1). This commit is causing segfaults in
> the case where this Git command does not load delta islands at all, e.g.
> when reading object IDs from standard input. One such crash can be hit
> when using repacking multi-pack-indices with delta islands enabled.
>
> The root cause of this bug is that we unconditionally dereference the
> `island_marks` variable even in the case where it is a `NULL` pointer,
> which is fixed by making it conditional. Note that we still leave the
> logic in place to set the pointer to `-1` to detect use-after-free bugs
> even when there are no loaded island marks at all.
> ---

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