netdev - Re: [PATCH 3/3] netlink: Lock out table resizes while dumping Netlink sockets

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Message-ID: <20150121095634.GO20315@casper.infradead.org>
Date:	Wed, 21 Jan 2015 09:56:34 +0000
From:	Thomas Graf <tgraf@...g.ch>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Patrick McHardy <kaber@...sh.net>, davem@...emloft.net,
	paulmck@...ux.vnet.ibm.com, ying.xue@...driver.com,
	netdev@...r.kernel.org, netfilter-devel@...r.kernel.org
Subject: Re: [PATCH 3/3] netlink: Lock out table resizes while dumping
 Netlink sockets

On 01/21/15 at 08:14pm, Herbert Xu wrote:
> On Wed, Jan 21, 2015 at 04:15:55PM +1100, Herbert Xu wrote:
> > I failed to address the security aspect of this approach.  Obviously
> > this can only work if the only entites doing the walk are trusted.
> > Which means that the vast majority (if not all) hash table users
> > would be excluded, in particular, netlink.
> 
> OK maybe we can get around this.  So we will postpone the resize
> or rehash when a walk is in place, however, when we hit a hard
> limit, i.e., when insert would otherwise fail, then we do the
> rehash regardless of any outstanding walks.  The walks will just
> behave erratically or we could force them to start from scratch
> again.

Exactly. I think we also need a timer to abort walks because if
only a single walker is allowed, an attacker could start a walk and
not complete it to block out everybody else.
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