Re: bug report: "git pack-redundant --all" crash in minimize()

[Jiang Xin <worldhello.net@gmail.com>]

Jeff King <peff@peff.net> 于2020年12月16日周三 上午2:24写道：
>
> On Tue, Dec 15, 2020 at 06:34:53PM +0100, Daniel C. Klauer wrote:
>
> > I'm getting the following crash from "git pack-redundant --all" (output
> > from valgrind):
> >
> > ==14070== Invalid read of size 8
> > ==14070==    at 0x18F165: minimize (pack-redundant.c:399)
> > ==14070==    by 0x18F165: cmd_pack_redundant (pack-redundant.c:622)
> > ==14070==    by 0x1242D3: run_builtin (git.c:444)
> > ==14070==    by 0x1242D3: handle_builtin (git.c:674)
> > ==14070==    by 0x125393: run_argv (git.c:741)
> > ==14070==    by 0x125393: cmd_main (git.c:872)
> > ==14070==    by 0x123E7D: main (common-main.c:52)
> > ==14070==  Address 0x10 is not stack'd, malloc'd or (recently) free'd
> >
> > Commands to reproduce:
> >
> > mkdir new
> > cd new
> > git init
> > touch foo.txt
> > git add foo.txt
> > git commit -m "first commit"
> > git gc
> > git pack-redundant --all
>
> Thanks for an easy reproduction. This bisects to 3011177640
> (pack-redundant: delay creation of unique_objects, 2019-02-02).
>
> I suspect the fix is just:
>
> diff --git a/builtin/pack-redundant.c b/builtin/pack-redundant.c
> index 3e70f2a4c1..68afcfeb7b 100644
> --- a/builtin/pack-redundant.c
> +++ b/builtin/pack-redundant.c
> @@ -396,7 +396,7 @@ static void minimize(struct pack_list **min)
>
>         pl = local_packs;
>         while (pl) {
> -               if (pl->unique_objects->size)
> +               if (pl->unique_objects && pl->unique_objects->size)
>                         pack_list_insert(&unique, pl);
>                 else
>                         pack_list_insert(&non_unique, pl);
>
> but I didn't look closely (author cc'd).
>

Will fix like this:

    pack-redundant: fix crash when one packfile in repo

    Command `git pack-redundant --all` will crash if there is only one
    packfile in the repository.  This is because, if there is only one
    packfile in local_packs, `cmp_local_packs` will do nothing and will
    leave `pl->unique_objects` as uninitialized.

    ... ...

diff --git a/builtin/pack-redundant.c b/builtin/pack-redundant.c
index 178e3409b7..9b0646a5e2 100644
--- a/builtin/pack-redundant.c
+++ b/builtin/pack-redundant.c
@@ -473,6 +473,12 @@ static void cmp_local_packs(void)
 {
        struct pack_list *subset, *pl = local_packs;

+       /* only one packfile */
+       if (!pl->next && !pl->unique_objects) {
+               llist_init(&pl->unique_objects);
+               return;
+       }
+
        while ((subset = pl)) {
                while ((subset = subset->next))
                        cmp_two_packs(pl, subset);