Re: [PATCH 08/10] unpack-trees: don't leak memory in verify_clean_subdirectory()

[Elijah Newren <newren@gmail.com>]

On Sun, Oct 3, 2021 at 5:46 PM Ævar Arnfjörð Bjarmason <avarab@gmail.com> wrote:
>
> Fix two different but related memory leaks in
> verify_clean_subdirectory(). We leaked both the "pathbuf" if
> read_directory() returned non-zero, and we never cleaned up our own
> "struct dir_struct" either.
>
>  * "pathbuf": When the read_directory() call followed by the
>    free(pathbuf) was added in c81935348be (Fix switching to a branch
>    with D/F when current branch has file D., 2007-03-15) we didn't
>    bother to free() before we called die().
>
>    But when this code was later libified in 203a2fe1170 (Allow callers
>    of unpack_trees() to handle failure, 2008-02-07) we started to leak
>    as we returned data to the caller. This fixes that memory leak,
>    which can be observed under SANITIZE=leak with e.g. the
>    "t1001-read-tree-m-2way.sh" test.
>
>  * "struct dir_struct": We've leaked the dir_struct ever since this
>    code was added back in c81935348be.
>
>    When that commit was written there wasn't an equivalent of
>    dir_clear(). Since it was added in 270be816049 (dir.c: provide
>    clear_directory() for reclaiming dir_struct memory, 2013-01-06)
>    we've omitted freeing the memory allocated here.
>
>    This memory leak could also be observed under SANITIZE=leak and the
>    "t1001-read-tree-m-2way.sh" test.
>
> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
> ---
>  unpack-trees.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/unpack-trees.c b/unpack-trees.c
> index bea598c9ece..260e7ec5bb4 100644
> --- a/unpack-trees.c
> +++ b/unpack-trees.c
> @@ -2138,9 +2138,10 @@ static int verify_clean_subdirectory(const struct cache_entry *ce,
>
>         d.exclude_per_dir = o->dir.exclude_per_dir;
>         i = read_directory(&d, o->src_index, pathbuf, namelen+1, NULL);
> +       dir_clear(&d);
> +       free(pathbuf);
>         if (i)
>                 return add_rejected_path(o, ERROR_NOT_UPTODATE_DIR, ce->name);
> -       free(pathbuf);
>         return cnt;
>  }
>
> --
> 2.33.0.1404.g83021034c5d

Good catches, and nicely explained.