From: "SZEDER Gábor" <szeder.dev@gmail.com>
To: Johannes Sixt <j6t@kdbg.org>
Cc: phillip.wood@dunelm.org.uk, Junio C Hamano <gitster@pobox.com>,
git@vger.kernel.org
Subject: Re: [PATCH] name-rev: avoid cutoff timestamp underflow
Date: Tue, 24 Sep 2019 09:21:59 +0200 [thread overview]
Message-ID: <20190924072159.GD2637@szeder.dev> (raw)
In-Reply-To: <fe58f33f-a3ae-4981-5bb7-d1659f3ab189@kdbg.org>
On Mon, Sep 23, 2019 at 09:16:26PM +0200, Johannes Sixt wrote:
> Am 23.09.19 um 10:37 schrieb SZEDER Gábor:
> > On Sun, Sep 22, 2019 at 11:01:26PM +0200, Johannes Sixt wrote:
> >> Huh? For signed cutoff and positive CUTOFF_DATE_SLOP,
> >> cutoff - CUTOFF_DATE_SLOP < cutoff is ALWAYS true. Signed interger
> >> underflow is undefined behavior and signed integer arithmetic does not
> >> wrap around!
> >>
> >> IOW, the new condition makes only sense today, because cutoff is an
> >> unsigned type, but breaks down should we switch to a signed type.
> >
> > Yeah, that's what I meant with worrying about signed underflow in the
> > commit message. As long as the cutoff is at least a day later than
> > the minimum value of our future signed 'timestamp_t', the condition
> > does the right thing. And considering that oldest time a signed 64
> > bit timestamp can represent far exceeds the age of the universe, and
> > the oldest value of even a signed 32 bit timestamp is almost half the
> > age of the Earth, I wasn't too worried.
>
> Note that commits and timestamps can be forged easily. I'm not worried
> that Git does not work "correctly" with forged timestamps (as long as it
> is not exploitable); but when it is simple to make foolproof, we should
> do it.
>
> BTW, 32-bit timestamps cover just ~135 years (not half the age of
> Earth).
Gah, forgot the division with seconds/year when calculating the range
of the 32bit timestamp.
> That's too little for people who want to store historic
> documents in a Git repository.
Indeed, but 'timestamp_t' is defined as 'uintmax_t', and we have the
Makefile knob 'NO_UINTMAX_T', in which case 'uintmax_t' is defined as
'uint32_t'...
next prev parent reply other threads:[~2019-09-24 7:22 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-22 18:01 [PATCH] name-rev: avoid cutoff timestamp underflow SZEDER Gábor
2019-09-22 18:57 ` Phillip Wood
2019-09-22 19:53 ` SZEDER Gábor
2019-09-22 21:01 ` Johannes Sixt
2019-09-23 8:37 ` SZEDER Gábor
2019-09-23 9:30 ` Phillip Wood
2019-09-23 19:16 ` Johannes Sixt
2019-09-24 7:21 ` SZEDER Gábor [this message]
2019-09-23 1:42 ` brian m. carlson
2019-09-23 8:39 ` SZEDER Gábor
2019-09-24 7:32 ` SZEDER Gábor
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190924072159.GD2637@szeder.dev \
--to=szeder.dev@gmail.com \
--cc=git@vger.kernel.org \
--cc=gitster@pobox.com \
--cc=j6t@kdbg.org \
--cc=phillip.wood@dunelm.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).