Re: [PATCH] lsm: make security_socket_getpeersec_stream() sockptr_t safe

From: Jakub Kicinski <kuba@kernel.org>
To: Paul Moore <paul@paul-moore.com>
Cc: linux-security-module@vger.kernel.org, selinux@vger.kernel.org,
	netdev@vger.kernel.org,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>
Subject: Re: [PATCH] lsm: make security_socket_getpeersec_stream() sockptr_t safe
Date: Thu, 13 Oct 2022 08:53:33 -0700	[thread overview]
Message-ID: <20221013085333.26288e44@kernel.org> (raw)
In-Reply-To: <166543910984.474337.2779830480340611497.stgit@olly>

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.