linux-kernel - Re: [PATCH] ipv4: tcp: security_sk_alloc() needed for unicast

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Date:	Thu, 09 Aug 2012 19:46:13 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Eric Paris <eparis@...isplace.org>
Cc:	Paul Moore <paul@...l-moore.com>,
	David Miller <davem@...emloft.net>,
	Casey Schaufler <casey@...aufler-ca.com>,
	John Stultz <johnstul@...ibm.com>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	lkml <linux-kernel@...r.kernel.org>,
	James Morris <james.l.morris@...cle.com>,
	selinux@...ho.nsa.gov, john.johansen@...onical.com,
	LSM <linux-security-module@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] ipv4: tcp: security_sk_alloc() needed for unicast_sock

On Thu, 2012-08-09 at 12:05 -0400, Eric Paris wrote:
> On Thu, Aug 9, 2012 at 11:36 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> > On Thu, 2012-08-09 at 11:07 -0400, Paul Moore wrote:
> >
> >> Is is possible to do the call to security_sk_alloc() in the ip_init() function
> >> or does the per-cpu nature of the socket make this a pain?
> >>
> >
> > Its a pain, if we want NUMA affinity.
> >
> > Here, each cpu should get memory from its closest node.
> 
> I really really don't like it.  I won't say NAK, but it is the first
> and only place in the kernel where I believe we allocate an object and
> don't allocate the security blob until some random later point in
> time.

...

>   If it is such a performance issue to have the security blob in
> the same numa node, isn't adding a number of branches and putting this
> function call on every output at least as bad?  Aren't we discouraged
> from GFP_ATOMIC?  In __init we can use GFP_KERNEL.

What a big deal. Its done _once_ time per cpu, and this is so small blob
of memory you'll have to show us one single failure out of one million
boots.

If the security_sk_alloc() fails, we dont care. We are about sending a
RESET or ACK packet. They can be lost by the network, or even skb
allocation can fail. Nobody ever noticed and complained.

Every time we accept() a new socket (and call security_sk_alloc()), its
done under soft irq, thus GFP_ATOMIC, and you didn't complain yet, while
a socket needs about 2 Kbytes of memory...

> 
> This still doesn't fix these sockets entirely.  We now have the
> security blob allocated, but it was never set to something useful.
> Paul, are you looking into this?  This is a bandaide, not a fix....
> 

Please do so, on a followup patch, dont pretend I must fix all this
stuff.


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