linux-kernel - Re: [PATCH 4/6] rhashtable: allow a walk of the hash table without missing objects.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <87sh8l428o.fsf@notabene.neil.brown.name>
Date:   Wed, 28 Mar 2018 08:50:31 +1100
From:   NeilBrown <neilb@...e.com>
To:     David Miller <davem@...emloft.net>
Cc:     tgraf@...g.ch, herbert@...dor.apana.org.au, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/6] rhashtable: allow a walk of the hash table without missing objects.

On Tue, Mar 27 2018, David Miller wrote:

> From: NeilBrown <neilb@...e.com>
> Date: Tue, 27 Mar 2018 10:33:04 +1100
>
>> In many cases where the walker needs to drop out of RCU protection,
>> it will take a reference to the object and this can prevent it from
>> being removed from the hash table.  In those cases, the last-returned
>> object can still be used as a cursor.  rhashtable cannot detect
>> these cases itself.
>
> Merely having an elevated reference count does not explicitly prevent
> the object from being removed from the hash table.
>
> This invariant might hold for the particular user of the rhashtable
> instance, but it is not always the case.

Agreed.  Hence "In many case ... this *can* be prevented" and "In those
cases".

The doc comment for rhashtable_walk_start_continue() makes it clear
that:

 *   The
 * previously returned object must still be in the hash table, and must be
 * provided as an argument.

Thanks,
NeilBrown

Download attachment "signature.asc" of type "application/pgp-signature" (833 bytes)