Re: [quicwg/base-drafts] Fix for #3187 (#3188)

Martin Thomson <notifications@github.com> Mon, 04 November 2019 23:58 UTC

Return-Path: <noreply@github.com>
X-Original-To: quic-issues@ietfa.amsl.com
Delivered-To: quic-issues@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id DD540120131 for <quic-issues@ietfa.amsl.com>; Mon, 4 Nov 2019 15:58:21 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -7.999
X-Spam-Level:
X-Spam-Status: No, score=-7.999 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, HTML_IMAGE_ONLY_32=0.001, HTML_MESSAGE=0.001, MAILING_LIST_MULTI=-1, RCVD_IN_DNSWL_HI=-5, SPF_HELO_NONE=0.001, SPF_PASS=-0.001] autolearn=ham autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (1024-bit key) header.d=github.com
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id eExU2oNklHzI for <quic-issues@ietfa.amsl.com>; Mon, 4 Nov 2019 15:58:20 -0800 (PST)
Received: from out-22.smtp.github.com (out-22.smtp.github.com [192.30.252.205]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 87FD2120888 for <quic-issues@ietf.org>; Mon, 4 Nov 2019 15:58:20 -0800 (PST)
Received: from github-lowworker-cd7bc13.ac4-iad.github.net (github-lowworker-cd7bc13.ac4-iad.github.net [10.52.25.102]) by smtp.github.com (Postfix) with ESMTP id 83B3AA041C for <quic-issues@ietf.org>; Mon, 4 Nov 2019 15:58:19 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=github.com; s=pf2014; t=1572911899; bh=QV3/G4jRntrHfwlohnXTWDP+rVhUmfBVzRa//hj6fCU=; h=Date:From:Reply-To:To:Cc:In-Reply-To:References:Subject:List-ID: List-Archive:List-Post:List-Unsubscribe:From; b=S3vM5LPh8CmY6Nd/YZacx0bYznrcV6D65Ygd7tu7+T7Z6ZTQQ5zwZ+V4/2votEOIY aT+g+cIwR7FlyiaIZRZ2aJ1cm0taLUs14AsPyUdLXX+N9TN8oJGOHueYX2NSMXywYR hy/LDq7fNgntuEab5D4IQt038K5FEIoge6Fv9Ys8=
Date: Mon, 04 Nov 2019 15:58:19 -0800
From: Martin Thomson <notifications@github.com>
Reply-To: quicwg/base-drafts <reply+AFTOJKYX2ZDFTCIZDVSL65V3ZXWZXEVBNHHB5VNYOQ@reply.github.com>
To: quicwg/base-drafts <base-drafts@noreply.github.com>
Cc: Subscribed <subscribed@noreply.github.com>
Message-ID: <quicwg/base-drafts/pull/3188/review/311433258@github.com>
In-Reply-To: <quicwg/base-drafts/pull/3188@github.com>
References: <quicwg/base-drafts/pull/3188@github.com>
Subject: Re: [quicwg/base-drafts] Fix for #3187 (#3188)
Mime-Version: 1.0
Content-Type: multipart/alternative; boundary="--==_mimepart_5dc0bb1b755ee_2f4d3fdc82ecd968358114"; charset="UTF-8"
Content-Transfer-Encoding: 7bit
Precedence: list
X-GitHub-Sender: martinthomson
X-GitHub-Recipient: quic-issues
X-GitHub-Reason: subscribed
X-Auto-Response-Suppress: All
X-GitHub-Recipient-Address: quic-issues@ietf.org
Archived-At: <https://mailarchive.ietf.org/arch/msg/quic-issues/jvwq91qeprnPkTDdXRDA261KY-w>
X-BeenThere: quic-issues@ietf.org
X-Mailman-Version: 2.1.29
List-Id: Notification list for GitHub issues related to the QUIC WG <quic-issues.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/quic-issues>, <mailto:quic-issues-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/quic-issues/>
List-Post: <mailto:quic-issues@ietf.org>
List-Help: <mailto:quic-issues-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/quic-issues>, <mailto:quic-issues-request@ietf.org?subject=subscribe>
X-List-Received-Date: Mon, 04 Nov 2019 23:58:22 -0000

martinthomson approved this pull request.



> +   // Note the extra check for overflow when candidate_pn
+   // is near MAX_PACKET_NUMBER

I think that we can use a single comment here for both.
```c
// Extra checks are required to prevent overflow and underflow.
```

> @@ -6057,12 +6057,15 @@ DecodePacketNumber(largest_pn, truncated_pn, pn_nbits):
    // The following code calculates a candidate value and
    // makes sure it's within the packet number window.
    candidate_pn = (expected_pn & ~pn_mask) | truncated_pn
-   if candidate_pn <= expected_pn - pn_hwin:
+   // Note the extra check for overflow when candidate_pn
+   // is near MAX_PACKET_NUMBER
+   if candidate_pn <= expected_pn - pn_hwin and
+      candidate_pn + pn_win < 1 << 62:

If the intent is to avoid overflow, then it might be a good idea to avoid overflow on intermediate values also:

```suggestion
      candidate_pn < (1 << 62) - pn_win:
```

-- 
You are receiving this because you are subscribed to this thread.
Reply to this email directly or view it on GitHub:
https://github.com/quicwg/base-drafts/pull/3188#pullrequestreview-311433258