netdev - Re: [PATCH] Use unsigned variables for packet lengths in ip[6]

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Message-ID: <20110602192457.GA19342@redhat.com>
Date:	Thu, 2 Jun 2011 15:24:57 -0400
From:	Dave Jones <davej@...hat.com>
To:	netdev@...r.kernel.org
Subject: Re: [PATCH] Use unsigned variables for packet lengths in ip[6]_queue.

On Fri, May 27, 2011 at 08:36:51PM -0400, Dave Jones wrote:

 >  > > Not catastrophic, but ipqueue seems to be too trusting of what it gets
 >  > > passed from userspace, and passes it on down to the page allocator,
 >  > > where it will spew warnings if the page order is too high.
 >  > > 
 >  > > __ipq_rcv_skb has several checks for lengths too small, but doesn't
 >  > > seem to have any for oversized ones.   I'm not sure what the maximum
 >  > > we should check for is. I'll code up a diff if anyone has any ideas
 >  > > on a sane maximum.
 >  > 
 >  > Maybe the thing to do is to simply pass __GFP_NOWARN to nlmsg_new()
 >  > in netlink_ack()?
 >  > 
 >  > Anyone else have a better idea?
 > 
 > So I went back to this today, and found something that doesn't look right.
 > After adding some instrumentation, and re-running my tests, I found that
 > the reason we were blowing up with enormous allocations was that we
 > were passing down a nlmsglen's like -1061109568
 > 
 > Is there any reason for that to be signed ?
 > The nlmsg_len entry of nlmsghdr is a u32, so I'm assuming this is a bug.
 > 
 > With the patch below, I haven't been able to reproduce the problem, but
 > I don't know if I've inadvertantly broken some other behaviour somewhere
 > deeper in netlink where this is valid.

any feedback on this ? am I barking up the wrong tree ?

	Dave

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