netdev - Re: [PATCH] selinux: Read sk->sk_family once in selinux_socket

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Message-ID: <CAHC9VhRT3VSvWbecSa5pnWMUkgmFVCAiMn=OtguHr_GCYcYbzw@mail.gmail.com>
Date: Fri, 13 Dec 2024 15:09:16 -0500
From: Paul Moore <paul@...l-moore.com>
To: Mikhail Ivanov <ivanov.mikhail1@...wei-partners.com>
Cc: Stephen Smalley <stephen.smalley.work@...il.com>, Mickaël Salaün <mic@...ikod.net>, 
	selinux@...r.kernel.org, omosnace@...hat.com, 
	linux-security-module@...r.kernel.org, netdev@...r.kernel.org, 
	yusongping@...wei.com, artem.kuzin@...wei.com, 
	konstantin.meskhidze@...wei.com
Subject: Re: [PATCH] selinux: Read sk->sk_family once in selinux_socket_bind()

On Fri, Dec 13, 2024 at 11:40 AM Mikhail Ivanov
<ivanov.mikhail1@...wei-partners.com> wrote:
> On 12/13/2024 6:46 PM, Stephen Smalley wrote:
> > On Fri, Dec 13, 2024 at 5:57 AM Mikhail Ivanov
> > <ivanov.mikhail1@...wei-partners.com> wrote:
> >>
> >> On 12/12/2024 8:50 PM, Mickaël Salaün wrote:
> >>> This looks good be there are other places using sk->sk_family that
> >>> should also be fixed.
> >>
> >> Thanks for checking this!
> >>
> >> For selinux this should be enough, I haven't found any other places
> >> where sk->sk_family could be read from an IPv6 socket without locking.
> >>
> >> I also would like to prepare such fix for other LSMs (apparmor, smack,
> >> tomoyo) (in separate patches).
> >
> > I'm wondering about the implications for SELinux beyond just
> > sk->sk_family access, e.g. SELinux maps the (family, type, protocol)
> > triple to a security class at socket creation time via
> > socket_type_to_security_class() and caches the security class in the
> > inode_security_struct and sk_security_struct for later use.
>
> IPv6 and IPv4 TCP sockets are mapped to the same SECCLASS_TCP_SOCKET
> security class. AFAICS there is no other places that can be affected by
> the IPV6_ADDFORM transformation.

Yes, thankfully we don't really encode the IP address family in any of
the SELinux object classes so that shouldn't be an issue.  I also
don't think we have to worry about the per-packet labeling protocols
as it's too late in the communication to change the socket's
associated packet labeling, it's either working or it isn't; we should
handle the mapped IPv4 address already.

I am a little concerned about bind being the only place where we have
to worry about accessing sk_family while the socket isn't locked.  As
an example, I'm a little concerned about the netfilter code paths; I
haven't chased them down, but my guess is that the associated
socket/sock isn't locked in those cases (in the relevant output and
postroute cases, forward should be a non-issue).

How bad is the performance impact of READ_ONCE()?  In other words, how
stupid would it be to simply do all of our sock->sk_family lookups
using READ_ONCE()?

-- 
paul-moore.com