René Scharfe <l.s.r@xxxxxx> writes:
> xdl_get_hunk() calculates the maximum number of common lines between two
> changes that would fit into the same hunk for the given context options.
> It involves doubling and addition and thus can overflow if the terms are
> huge.
>
> The type of ctxlen and interhunkctxlen in xdemitconf_t is long, while
> the type of the corresponding context and interhunkcontext in struct
> diff_options is int. On many platforms longs are bigger that ints,
> which prevents the overflow. On Windows they have the same range and
> the overflow manifests as hunks that are split erroneously and lines
> being repeated between them.
>
> Fix the overflow by checking and not going beyond LONG_MAX. This allows
> specifying a huge context line count and getting all lines of a changed
> files in a single hunk, as expected.
>
> Reported-by: Jason Cho <jason11choca@xxxxxxxxx>
> Signed-off-by: René Scharfe <l.s.r@xxxxxx>
> ---
> t/t4055-diff-context.sh | 10 ++++++++++
> xdiff/xemit.c | 8 +++++++-
> 2 files changed, 17 insertions(+), 1 deletion(-)
Oh, I love a patch like this that is well thought out to carefully
check the bounds, instead of blindly say "ah, counting number of
things in size_t solves everything" ;-)
> diff --git a/xdiff/xemit.c b/xdiff/xemit.c
> index f8e3f25b03..1d40c9cb40 100644
> --- a/xdiff/xemit.c
> +++ b/xdiff/xemit.c
> @@ -43,6 +43,10 @@ static int xdl_emit_record(xdfile_t *xdf, long ri, char const *pre, xdemitcb_t *
> return 0;
> }
>
> +static long saturating_add(long a, long b)
> +{
> + return signed_add_overflows(a, b) ? LONG_MAX : a + b;
> +}
>
> /*
> * Starting at the passed change atom, find the latest change atom to be included
> @@ -52,7 +56,9 @@ static int xdl_emit_record(xdfile_t *xdf, long ri, char const *pre, xdemitcb_t *
> xdchange_t *xdl_get_hunk(xdchange_t **xscr, xdemitconf_t const *xecfg)
> {
> xdchange_t *xch, *xchp, *lxch;
> - long max_common = 2 * xecfg->ctxlen + xecfg->interhunkctxlen;
> + long max_common = saturating_add(saturating_add(xecfg->ctxlen,
> + xecfg->ctxlen),
> + xecfg->interhunkctxlen);
Looking good.
Thanks. Will queue.
