netdev - Re: [PATCH net 2/3] net: sctp: fix panic on duplicate ASCONF chunks

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Message-ID: <20141015025833.GA6493@localhost.localdomain>
Date:	Tue, 14 Oct 2014 22:58:34 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Daniel Borkmann <dborkman@...hat.com>
Cc:	davem@...emloft.net, linux-sctp@...r.kernel.org,
	netdev@...r.kernel.org, Vlad Yasevich <vyasevich@...il.com>
Subject: Re: [PATCH net 2/3] net: sctp: fix panic on duplicate ASCONF chunks

On Mon, Oct 13, 2014 at 01:25:11AM +0200, Daniel Borkmann wrote:
> On 10/12/2014 03:42 AM, Neil Horman wrote:
> >On Sat, Oct 11, 2014 at 12:02:31AM +0200, Daniel Borkmann wrote:
> >>On 10/10/2014 05:39 PM, Neil Horman wrote:
> >>...
> >>>Is it worth adding a WARN_ON, to indicate that two ASCONF chunks have been
> >>>received with duplicate serials?
> >>
> >>Don't think so, as this would be triggerable from outside.
> >>
> >WARN_ON_ONCE then, per serial number?
> 
> Sorry, but no. If someone seriously runs that in production and it
> triggers a WARN() from outside, admins will start sending us bug
> reports that apparently something with the kernel code is wrong.
> 
> WARN() should only be used if we have some *internal* unexpected bug,
> but can still fail gracefully. This would neither be an actual code bug
> nor would it be an internally triggered one, plus we add unnecessary
> complexity to the code. Similarly, for those reasons we don't WARN()
> and throw a stack trace when we receive, say, an skb of invalid length
> elsewhere.
> 
> I'd also like to avoid any additional pr_debug().
> 
> I don't think people enable them in production, and if they really do,
> it's too late anyway as we already have received this chunk. If anything,
> I'd rather like to see debugging code further removed as we have already
> different facilities in the kernel for runtime debugging that are much
> more powerful.
What do you suggest then?  It seems like this is a protocol error that an
administrator will want to be made aware of.  I'm open to other options, but
just saying "no" isn't sufficient for me.
Neil

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