Re: [PATCH v2] fetch-pack: clear alternate shallow when complete

>
> When we write an alternate shallow file in update_shallow, we write it
> into the lock file. The string stored in alternate_shallow_file is
> copied from the lock file path, but it is freed the moment that the lock
> file is closed, since we call strbuf_release to free that path.
>
> This used to work, since we did not invoke git index-pack more than
> once. However, we now do, and starting with bd0b42aed3 (fetch-pack: do
> not take shallow lock unnecessarily - 2019-01-10), we no longer reset
> this value unconditionally; consequently, we reuse the freed memory.
> Ensure we reset the value to NULL to avoid using freed memory. git
> index-pack will read the repository's shallow file, which will have been
> updated with the correct information.

>
> Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
> ---
>  fetch-pack.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/fetch-pack.c b/fetch-pack.c
> index 577faa6229..a92621a388 100644
> --- a/fetch-pack.c
> +++ b/fetch-pack.c
> @@ -1272,6 +1272,8 @@ static void receive_shallow_info(struct fetch_pack_args *args,
>                 setup_alternate_shallow(&shallow_lock, &alternate_shallow_file,
>                                         NULL);
>                 args->deepen = 1;
> +       } else {
> +               alternate_shallow_file = NULL;
>         }
>  }
>
> @@ -1489,6 +1491,7 @@ static void update_shallow(struct fetch_pack_args *args,
>                         rollback_lock_file(&shallow_lock);
>                 } else
>                         commit_lock_file(&shallow_lock);
> +               alternate_shallow_file = NULL;
>                 return;
>         }
>
> @@ -1512,6 +1515,7 @@ static void update_shallow(struct fetch_pack_args *args,
>                                                 &alternate_shallow_file,
>                                                 &extra);
>                         commit_lock_file(&shallow_lock);
> +                       alternate_shallow_file = NULL;
>                 }
>                 oid_array_clear(&extra);
>                 return;
> @@ -1551,6 +1555,7 @@ static void update_shallow(struct fetch_pack_args *args,
>                 commit_lock_file(&shallow_lock);
>                 oid_array_clear(&extra);
>                 oid_array_clear(&ref);
> +               alternate_shallow_file = NULL;
>                 return;
>         }
>