netdev - Re: [PATCH net] selinux: do not report error on connect(AF

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Message-ID: <36e13dc4-be40-d1f6-0be5-32cd4fc38f6e@tycho.nsa.gov>
Date:   Wed, 8 May 2019 14:12:09 -0400
From:   Stephen Smalley <sds@...ho.nsa.gov>
To:     Paolo Abeni <pabeni@...hat.com>, Paul Moore <paul@...l-moore.com>
Cc:     selinux@...r.kernel.org, netdev@...r.kernel.org,
        Tom Deseyn <tdeseyn@...hat.com>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Richard Haines <richard_c_haines@...nternet.com>
Subject: Re: [PATCH net] selinux: do not report error on connect(AF_UNSPEC)

On 5/8/19 9:32 AM, Paolo Abeni wrote:
> calling connect(AF_UNSPEC) on an already connected TCP socket is an
> established way to disconnect() such socket. After commit 68741a8adab9
> ("selinux: Fix ltp test connect-syscall failure") it no longer works
> and, in the above scenario connect() fails with EAFNOSUPPORT.
> 
> Fix the above falling back to the generic/old code when the address family
> is not AF_INET{4,6}, but leave the SCTP code path untouched, as it has
> specific constraints.
> 
> Fixes: 68741a8adab9 ("selinux: Fix ltp test connect-syscall failure")
> Reported-by: Tom Deseyn <tdeseyn@...hat.com>
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> ---
>   security/selinux/hooks.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index c61787b15f27..d82b87c16b0a 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -4649,7 +4649,7 @@ static int selinux_socket_connect_helper(struct socket *sock,
>   		struct lsm_network_audit net = {0,};
>   		struct sockaddr_in *addr4 = NULL;
>   		struct sockaddr_in6 *addr6 = NULL;
> -		unsigned short snum;
> +		unsigned short snum = 0;
>   		u32 sid, perm;
>   
>   		/* sctp_connectx(3) calls via selinux_sctp_bind_connect()
> @@ -4674,12 +4674,12 @@ static int selinux_socket_connect_helper(struct socket *sock,
>   			break;
>   		default:
>   			/* Note that SCTP services expect -EINVAL, whereas
> -			 * others expect -EAFNOSUPPORT.
> +			 * others must handle this at the protocol level:
> +			 * connect(AF_UNSPEC) on a connected socket is
> +			 * a documented way disconnect the socket.
>   			 */
>   			if (sksec->sclass == SECCLASS_SCTP_SOCKET)
>   				return -EINVAL;
> -			else
> -				return -EAFNOSUPPORT;

I think we need to return 0 here.  Otherwise, we'll fall through with an 
uninitialized snum, triggering a random/bogus permission check.

>   		}
>   
>   		err = sel_netport_sid(sk->sk_protocol, snum, &sid);
>