netdev - Re: [PATCH] lsm: make security_socket_getpeersec_stream() sockptr

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Date:   Thu, 13 Oct 2022 11:59:47 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     linux-security-module@...r.kernel.org, selinux@...r.kernel.org,
        netdev@...r.kernel.org,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Subject: Re: [PATCH] lsm: make security_socket_getpeersec_stream() sockptr_t safe

On Thu, Oct 13, 2022 at 11:53 AM Jakub Kicinski <kuba@...nel.org> wrote:
> On Mon, 10 Oct 2022 17:58:29 -0400 Paul Moore wrote:
> > Commit 4ff09db1b79b ("bpf: net: Change sk_getsockopt() to take the
> > sockptr_t argument") made it possible to call sk_getsockopt()
> > with both user and kernel address space buffers through the use of
> > the sockptr_t type.  Unfortunately at the time of conversion the
> > security_socket_getpeersec_stream() LSM hook was written to only
> > accept userspace buffers, and in a desire to avoid having to change
> > the LSM hook the commit author simply passed the sockptr_t's
> > userspace buffer pointer.  Since the only sk_getsockopt() callers
> > at the time of conversion which used kernel sockptr_t buffers did
> > not allow SO_PEERSEC, and hence the
> > security_socket_getpeersec_stream() hook, this was acceptable but
> > also very fragile as future changes presented the possibility of
> > silently passing kernel space pointers to the LSM hook.
> >
> > There are several ways to protect against this, including careful
> > code review of future commits, but since relying on code review to
> > catch bugs is a recipe for disaster and the upstream eBPF maintainer
> > is "strongly against defensive programming", this patch updates the
> > LSM hook, and all of the implementations to support sockptr_t and
> > safely handle both user and kernel space buffers.
>
> Code seems sane, FWIW, but the commit message sounds petty,
> which is likely why nobody is willing to ack it.

Heh, feel free to look at Alexei's comments to my original email; the
commit description seems spot on to me.

FWIW, once Casey and John give a thumbs up on their respective code
areas I do plan to pull this into the lsm/next tree with, or without,
any ACKs from the netdev/bpf folks.  It would be nice if I could get
an ACK from you guys, but since netdev/bpf feels comfortable merging
small security/ code without ACKs from the LSM folks, I see no problem
merging small netdev/bpf code with ACKs from the netdev/bpf folks.

-- 
paul-moore.com