netdev - Re: [PATCH net-2.6.25] Add packet filtering based on process'ssecurity context.

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Date:	Sat, 24 Nov 2007 11:14:50 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	jmorris@...ei.org
Cc:	herbert@...dor.apana.org.au, netdev@...r.kernel.org,
	davem@...emloft.net, linux-security-module@...r.kernel.org,
	kaber@...sh.net, netfilter-devel@...ts.netfilter.org,
	sds@...ho.nsa.gov
Subject: Re: [PATCH net-2.6.25] Add packet filtering based on process'ssecurity context.

Hello.

James Morris wrote:
> From memory, one approach under discussion was to add netfilter hooks to 
> the transport layer, which could be invoked correctly by each type of 
> protocol when the target process is selected.
> 
> If this is done for netfilter, then an LSM hook is probably not needed at 
> all, as security modules can utilize netfilter hooks directly.

Patrick McHardy says (at http://marc.info/?l=linux-netdev&m=118495005800410&w=2 )
"Even with socket filters netfilter doesn't know the final receipient
 process, that is not known until it calls recvmsg and the data is read,
 which is too late for netfilter."



> > Precautions: This approach has a side effect which unlikely occurs.
> > 
> > If a socket is shared by multiple processes with different policy,
> > the process who should be able to accept this connection
> > will not be able to accept this connection
> > because socket_post_accept() aborts this connection.
> > But if socket_post_accept() doesn't abort this connection,
> > the process who must not be able to accept this connection
> > will repeat accept() forever, which is a worse side effect.
I think this change is needed regardless of whether to use connection filtering or not.
Currently, SELinux doesn't use socket_post_accept().

|  * @socket_post_accept:
|  *	This hook allows a security module to copy security
|  *	information into the newly created socket's inode.

But if one wants to *copy* security information to accept()ed socket,
the location after fd_install() is too late to copy
because the userland process can access accept()ed socket's fd
whose security information is not copied yet.

Also, if one wants to *assign* security information to accept()ed socket,
it might attend memory allocation which can fail.
So, use of void for socket_post_accept() deprives a security module of a chance to
abort this connection if the security module failed to *assign* security information.

Regards.

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