netdev - Re: [PATCH v2] selinux: Fix error priority for bind with AF_UNSPEC on AF

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Message-ID: <CAHC9VhTrrJN9MRZD5XWXJiygq+jVN-xiRc-wkZP3tYB-2D+Frg@mail.gmail.com>
Date: Fri, 29 Dec 2023 16:52:23 -0500
From: Paul Moore <paul@...l-moore.com>
To: Mickaël Salaün <mic@...ikod.net>
Cc: Eric Paris <eparis@...isplace.org>, Stephen Smalley <stephen.smalley.work@...il.com>, 
	Günther Noack <gnoack@...gle.com>, 
	Konstantin Meskhidze <konstantin.meskhidze@...wei.com>, 
	Muhammad Usama Anjum <usama.anjum@...labora.com>, linux-security-module@...r.kernel.org, 
	netdev@...r.kernel.org
Subject: Re: [PATCH v2] selinux: Fix error priority for bind with AF_UNSPEC on
 AF_INET6 socket

On Fri, Dec 29, 2023 at 12:19 PM Mickaël Salaün <mic@...ikod.net> wrote:
>
> The IPv6 network stack first checks the sockaddr length (-EINVAL error)
> before checking the family (-EAFNOSUPPORT error).
>
> This was discovered thanks to commit a549d055a22e ("selftests/landlock:
> Add network tests").
>
> Cc: Eric Paris <eparis@...isplace.org>
> Cc: Konstantin Meskhidze <konstantin.meskhidze@...wei.com>
> Cc: Paul Moore <paul@...l-moore.com>
> Cc: Stephen Smalley <stephen.smalley.work@...il.com>
> Reported-by: Muhammad Usama Anjum <usama.anjum@...labora.com>
> Closes: https://lore.kernel.org/r/0584f91c-537c-4188-9e4f-04f192565667@collabora.com
> Fixes: 0f8db8cc73df ("selinux: add AF_UNSPEC and INADDR_ANY checks to selinux_socket_bind()")
> Signed-off-by: Mickaël Salaün <mic@...ikod.net>
> ---
>
> Changes since v1:
> https://lore.kernel.org/r/20231228113917.62089-1-mic@digikod.net
> * Use the "family" variable (suggested by Paul).
> ---
>  security/selinux/hooks.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index feda711c6b7b..748baa98f623 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -4667,6 +4667,9 @@ static int selinux_socket_bind(struct socket *sock, struct sockaddr *address, in
>                                 return -EINVAL;
>                         addr4 = (struct sockaddr_in *)address;
>                         if (family_sa == AF_UNSPEC) {
> +                               if (family == AF_INET6 &&
> +                                   addrlen < SIN6_LEN_RFC2133)
> +                                       return -EINVAL;

If we want to try and match the non-LSM PF_INET6 socket handling as
much as possible, after the length check (above) we should fail any
non AF_INET6 addresses on an INET6 sock, see __inet6_bind().

My guess is we want something like this:

  if (family == AF_INET6) {
    /* length check from inet6_bind_sk() */
    if (addrlen < SIN6_LEN_RFC2133)
      return -EINVAL;
    /* !AF_INET6 check from __inet6_bind() */
    goto err_af;
  }

>                                 /* see __inet_bind(), we only want to allow
>                                  * AF_UNSPEC if the address is INADDR_ANY
>                                  */
> --
> 2.43.0

-- 
paul-moore.com