public inbox for passt-dev@passt.top
 help / color / mirror / code / Atom feed
From: David Gibson <david@gibson.dropbear.id.au>
To: Stefano Brivio <sbrivio@redhat.com>
Cc: passt-dev@passt.top
Subject: Re: [PATCH v2 08/11] tcp: Remove unneccessary bounds check in tcp_timer_handler()
Date: Thu, 30 Nov 2023 11:42:33 +1100	[thread overview]
Message-ID: <ZWfaeYXnGJoJEbdX@zatzit> (raw)
In-Reply-To: <20231129153239.2df7ee71@elisabeth>

[-- Attachment #1: Type: text/plain, Size: 2036 bytes --]

On Wed, Nov 29, 2023 at 03:32:39PM +0100, Stefano Brivio wrote:
> On Mon, 27 Nov 2023 10:33:45 +1100
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
> > In tcp_timer_handler() we use conn_at_idx() to interpret the flow index
> > from the epoll reference.  However, this will never be NULL - we always
> > put a valid index into the epoll_ref.  Simplify slightly based on this.
> 
> Sorry, I missed this during review of v1.
> 
> I have mixed feeling about this, and I don't think 11/11 changes
> anything in this regard: we have to trust the kernel, as there's no
> benefit to security in not doing so.
> 
> At the same time, should we ever get an out-of-bounds index from the
> epoll event, we can fail gracefully here. Slightly worse, however: if
> we get a timer event for a connection that's already closed, we'll
> happily go and try to manipulate its timer (with or without the !conn
> check).

So, as you note this only verifies that the index is theoretically
possible.  It doesn't check that it's a valid index in the current
size of the connection table, it doesn't check if the connection is
already closed and it can't check if it's a stale index for a
different connection than the one originally intended, because the
table has been compacted.

Given all those potential failure modes, I don't see a lot of value in
checking if the index is wildly out of bounds, which would require a
kernel bug rather more extreme than those other possibilies.

> All in all, I think the check is minimally useful, and we should have
> something more robust than that. So if this patch helps keeping things
> simple later in the series, I don't see an issue with that, but perhaps
> we should add back a more sensible set of checks later.

Perhaps, yes.

> The next patches all look good to me.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

  reply	other threads:[~2023-11-30  0:55 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-11-26 23:33 [PATCH v2 00/11] Introduce unified flow table, first steps David Gibson
2023-11-26 23:33 ` [PATCH v2 01/11] flow, tcp: Generalise connection types David Gibson
2023-11-26 23:33 ` [PATCH v2 02/11] flow, tcp: Move TCP connection table to unified flow table David Gibson
2023-11-26 23:33 ` [PATCH v2 03/11] flow, tcp: Consolidate flow pointer<->index helpers David Gibson
2023-11-26 23:33 ` [PATCH v2 04/11] util: MAX_FROM_BITS() should be unsigned David Gibson
2023-11-26 23:33 ` [PATCH v2 05/11] flow: Make unified version of flow table compaction David Gibson
2023-11-26 23:33 ` [PATCH v2 06/11] flow, tcp: Add logging helpers for connection related messages David Gibson
2023-11-26 23:33 ` [PATCH v2 07/11] flow: Introduce 'sidx' type to represent one side of one flow David Gibson
2023-11-29 14:32   ` Stefano Brivio
2023-11-30  0:37     ` David Gibson
2023-11-30  9:21       ` Stefano Brivio
2023-12-01  0:10         ` David Gibson
2023-11-26 23:33 ` [PATCH v2 08/11] tcp: Remove unneccessary bounds check in tcp_timer_handler() David Gibson
2023-11-29 14:32   ` Stefano Brivio
2023-11-30  0:42     ` David Gibson [this message]
2023-11-26 23:33 ` [PATCH v2 09/11] flow,tcp: Generalise TCP epoll_ref to generic flows David Gibson
2023-11-26 23:33 ` [PATCH v2 10/11] tcp_splice: Use unsigned to represent side David Gibson
2023-11-26 23:33 ` [PATCH v2 11/11] flow,tcp: Use epoll_ref type including flow and side David Gibson

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=ZWfaeYXnGJoJEbdX@zatzit \
    --to=david@gibson.dropbear.id.au \
    --cc=passt-dev@passt.top \
    --cc=sbrivio@redhat.com \
    /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.
Code repositories for project(s) associated with this public inbox

	https://passt.top/passt

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 IMAP folder(s).