linux-kernel - Re: [PATCH RFC] LSM, net: Add SO

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Date: Fri, 21 Jun 2024 15:41:46 -0400
From: Paul Moore <paul@...l-moore.com>
To: Casey Schaufler <casey@...aufler-ca.com>
Cc: LSM List <linux-security-module@...r.kernel.org>, netdev@...r.kernel.org, 
	linux-api@...r.kernel.org, 
	Linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC] LSM, net: Add SO_PEERCONTEXT for peer LSM data

On Fri, Jun 21, 2024 at 12:06 PM Casey Schaufler <casey@...aufler-ca.com> wrote:
> On 6/20/2024 2:05 PM, Paul Moore wrote:
> > On May 13, 2024 Casey Schaufler <casey@...aufler-ca.com> wrote:

...

> >> +/**
> >> + * security_socket_getpeerctx_stream() - Get the remote peer label
> >> + * @sock: socket
> >> + * @optval: destination buffer
> >> + * @optlen: size of peer label copied into the buffer
> >> + * @len: maximum size of the destination buffer
> >> + *
> >> + * This hook allows the security module to provide peer socket security state
> >> + * for unix or connected tcp sockets to userspace via getsockopt
> >> + * SO_GETPEERCONTEXT.  For tcp sockets this can be meaningful if the socket
> >> + * is associated with an ipsec SA.
> >> + *
> >> + * Return: Returns 0 if all is well, otherwise, typical getsockopt return
> >> + *         values.
> >> + */
> >> +int security_socket_getpeerctx_stream(struct socket *sock, sockptr_t optval,
> >> +                                  sockptr_t optlen, unsigned int len)
> >> +{
> >> +    struct security_hook_list *hp;
> >> +
> >> +    hlist_for_each_entry(hp, &security_hook_heads.socket_getpeerctx_stream,
> >> +                         list)
> >> +            return hp->hook.socket_getpeerctx_stream(sock, optval, optlen,
> >> +                                                     len);
> >> +
> >> +    return LSM_RET_DEFAULT(socket_getpeerctx_stream);
> >> +}
> >
> > Don't we need the same magic that we have in security_getselfattr() to
> > handle the multi-LSM case?
>
> Yes. I would like to move this ahead independently of the multi-LSM support.
> Putting the multi-LSM magic in is unnecessary and rather pointless until then.

Starting with the LSM syscalls, I want any new user visible API that
can support multiple LSMs to have support for multiple LSMs.  Yes, the
setselfattr API doesn't support multiple LSMs, but that is because we
agreed there was never going to be a way to safely support that usage.
In this particular case, that same argument does not apply, we could
have multiple LSMs returning a socket's network peer information (even
if we don't currently see that), so let's make sure our API supports
it from the start.

Unrelated to the above, it would also be good to datagram support as a
patch 2/2 thing in a future version of this patchset.  Please be
careful not to carry over the mistakes we made with SCM_SECURITY (see
the GH discussion linked below).

* https://github.com/SELinuxProject/selinux-kernel/issues/24

-- 
paul-moore.com