Subject: Re: [PATCH] pack-bitmap: fix memory leak if `load_bitmap_entries_v1` failed

From: Junio C Hamano <[email-masked]>
Date: Wed, 14 May 2025 06:18:56 -0700

Taylor Blau <[email-masked]> writes:

> After going through the "failed" label, load_bitmap() will return -1,
> and its caller (either prepare_bitmap_walk() or prepare_bitmap_git())
> will then call free_bitmap_index().
>
> That function would have done:
>
>     struct stored_bitmap *sb;
>     kh_foreach_value(b->bitmaps, sb {
>       ewah_pool_free(sb->root);
>       free(sb);
>     });
>
> , but won't since load_bitmap() already called kh_destroy_oid_map() and
> NULL'd the "bitmaps" pointer from within its "failed" label.

Yikes.

> So I think if you got part of the way through loading bitmap entries and
> then failed, you would leak all of the previous entries that you were
> able to load successfully.
>
> I suspect the fix looks something like:
> ...
> --- 8< ---
> diff --git a/pack-bitmap.c b/pack-bitmap.c
> index 5299f49d59..7f28532a69 100644
> --- a/pack-bitmap.c
> +++ b/pack-bitmap.c
> @@ -631,41 +631,28 @@ static int load_bitmap(struct repository *r, struct bitmap_index *bitmap_git,
>  	bitmap_git->ext_index.positions = kh_init_oid_pos();
>
>  	if (load_reverse_index(r, bitmap_git))
> -		goto failed;
> +		return -1;

(a lot of changes that simplifies the code snipped)

> -failed:
> -	munmap(bitmap_git->map, bitmap_git->map_size);
> -	bitmap_git->map = NULL;
> -	bitmap_git->map_size = 0;
> -
> -	kh_destroy_oid_map(bitmap_git->bitmaps);
> -	bitmap_git->bitmaps = NULL;
> -
> -	kh_destroy_oid_pos(bitmap_git->ext_index.positions);
> -	bitmap_git->ext_index.positions = NULL;
> -
> -	return -1;
>  }
>
>  static int open_pack_bitmap(struct repository *r,
> --- >8 ---
>
> , since all callers of load_bitmap() will themselves call
> free_bitmap_index(), so there is no need for us to open-code a portion
> of that function's implementation ourselves.

It is rare for a fix to be removing and simplifying this much code
;-)