Re: [PATCH] Fix delta integer overflows

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi,

On Mon, 7 Aug 2017, Junio C Hamano wrote:

> Martin Koegler <martin.koegler@chello.at> writes:
> 
> > From: Martin Koegler <martin.koegler@chello.at>
> >
> > The current delta code produces incorrect pack objects for files > 4GB.
> >
> > Signed-off-by: Martin Koegler <martin.koegler@chello.at>
> > ---
> >  diff-delta.c | 23 ++++++++++++-----------
> >  1 file changed, 12 insertions(+), 11 deletions(-)
> >
> > Just pass any file > 4 GB to the delta-compression [by increasing the delta limits].
> > As file size, a truncated 32bit value will be encoded, leading to broken pack files.
> 
> The patch obviously makes the code better and self consistent in
> that "struct delta_index" has src_size as ulong, and this function
> takes trg_size as ulong, and it was plain wrong for the code to
> assume that "i", which is uint, can receive it safely.
> 
> In the longer term we might want to move to size_t or even
> uintmax_t, as the ulong on a platform may not be long enough in
> order to express the largest file size the platform can have, but
> this patch (1) is good even without such a change, and (2) gives a
> good foundation to build on if we want such a change on top.
> 
> Thanks.  Will queue.

This is sad. There is no "may not be long enough". We already know a
platform where unsigned long is not long enough, don't we? Why leave this
patch in this intermediate state?

If you want to work on data in memory, then size_t is the appropriate data
type. We already use it elsewhere. Let's use it here, too, without the
intermediate bump from the incorrect `int` to the equally incorrect
`long`.

Ciao,
Johannes