From: Junio C Hamano <junkio@cox.net>
Date: Thu, 05 Apr 2007 22:51:36 GMT
Subject: Re: [PATCH 02/13] declare overflow during base128 decoding when 1 MSB nonzero, not 7
Message-ID: <7vr6qymo3r.fsf@assigned-by-dhcp.cox.net>
In-Reply-To: <56b7f5510704051524p28eafc18mae3131ef13cdabfa@mail.gmail.com>

"Dana How" <danahow@gmail.com> writes:

> Subject: [PATCH 02/13] declare overflow during base128 decoding when 1 MSB nonzero, not 7
>
> ---
>  builtin-pack-objects.c   |    2 +-
>  builtin-unpack-objects.c |    2 +-
>  index-pack.c             |    2 +-
>  sha1_file.c              |    2 +-
>  4 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/builtin-pack-objects.c b/builtin-pack-objects.c
> index b5f9648..50246e1 100644
> --- a/builtin-pack-objects.c
> +++ b/builtin-pack-objects.c
> @@ -1014,7 +1014,7 @@ static void check_object(struct object_entry *entry)
>  				ofs = c & 127;
>  				while (c & 128) {
>  					ofs += 1;
> -					if (!ofs || ofs & ~(~0UL >> 7))
> +					if (!ofs || ofs & ~(~0UL >> 1))
>  						die("delta base offset overflow in pack for %s",
>  						    sha1_to_hex(entry->sha1));
>  					c = buf[used_0++];

The line after these context does this:

	ofs = (ofs << 7) + (c & 127);

If you do not check the top 7 bits, wouldn't you miss overflow?