Message-ID: <49A5D6D6.7080605@numericable.fr>
Date:	Thu, 26 Feb 2009 00:40:06 +0100
From:	etienne <etienne.basset@...ericable.fr>
To:	Paul Moore <paul.moore@...com>
CC:	Casey Schaufler <casey@...aufler-ca.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	LSM <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH][SMACK] add a socket_post_accept hook to fix netlabel
 issues with labeled TCP servers V1

Paul Moore wrote:
> On Tuesday 24 February 2009 06:36:59 pm Paul Moore wrote:
>> On Tuesday 24 February 2009 05:59:59 pm etienne wrote:
>>> Paul Moore wrote:
>>>> On Tuesday 24 February 2009 05:20:42 pm etienne wrote:
>>>>> Paul Moore wrote:
>>>>>> On Tuesday 24 February 2009 04:28:24 pm etienne wrote:
>>>>>>>  /**
>>>>>>> + * smack_socket_post_access - post access check
>>>>>>> + * @sock: the socket
>>>>>>> + * @newsock : the grafted sock
>>>>>>> + *
>>>>>>> + * we have to match client IP against smack_host_label()
>>>>>>> + */
>>>>>>> +static void  smack_socket_post_accept(struct socket *sock, struct
>>>>>>> socket *newsock) +{
>>>>>>> +	char *hostsp;
>>>>>>> +	struct sockaddr_storage address;
>>>>>>> +	struct sockaddr_in *sin;
>>>>>>> +	struct sockaddr_in6 *sin6;
>>>>>>> +	struct in6_addr *addr6;
>>>>>>> +	struct socket_smack *ssp = newsock->sk->sk_security;
>>>>>>> +	int len;
>>>>>>> +
>>>>>>> +	if (sock->sk == NULL)
>>>>>>> +		return;
>>>>>>> +
>>>>>>> +	/* sockets can listen on both IPv4 & IPv6,
>>>>>>> +	   and fallback to V4 if client is V4 */
>>>>>>> +	if  (newsock->sk->sk_family != AF_INET && newsock->sk->sk_family
>>>>>>> != AF_INET6) +		return;
>>>>>>> +
>>>>>>> +	/* get the client IP address **/
>>>>>>> +	newsock->ops->getname(newsock, (struct sockaddr *)&address, &len,
>>>>>>> 2); +
>>>>>>> +	switch (newsock->sk->sk_family) {
>>>>>>> +	case AF_INET:
>>>>>>> +		sin = (struct sockaddr_in *)&address;
>>>>>>> +		break;
>>>>>>> +	case AF_INET6:
>>>>>>> +		sin6  = (struct sockaddr_in6 *)&address;
>>>>>>> +		addr6 = &sin6->sin6_addr;
>>>>>>> +		/* if a V4 client connects to a V6 listening server,
>>>>>>> +		 * we will get a IPV6_ADDR_MAPPED mapped address here
>>>>>>> +		 * we have to handle this case too
>>>>>>> +		 * the test below is ipv6_addr_type()== IPV6_ADDR_MAPPED
>>>>>>> +		 * without the requirement to have IPv6 compiled in
>>>>>>> +		 */
>>>>>>> +		if ((addr6->s6_addr32[0] | addr6->s6_addr32[1]) == 0 &&
>>>>>>> +				addr6->s6_addr32[2] == htonl(0x0000ffff)) {
>>>>>>> +			__be32 addr = sin6->sin6_addr.s6_addr32[3];
>>>>>>> +			__be16 port = sin6->sin6_port;
>>>>>>> +			sin = (struct sockaddr_in *)&address;
>>>>>>> +			sin->sin_family = AF_INET;
>>>>>>> +			sin->sin_port = port;
>>>>>>> +			sin->sin_addr.s_addr = addr;
>>>>>>> +		} else {
>>>>>>> +			/* standard IPv6, we'll send unlabeled */
>>>>>>> +			smack_netlabel(newsock->sk, SMACK_UNLABELED_SOCKET);
>>>>>>> +			return;
>>>>>>> +		}
>>>>>>> +		break;
>>>>>>> +	default:
>>>>>>> +		/** not possible to be there **/
>>>>>>> +		return;
>>>>>>> +	}
>>>>>>> +	/* so, is there a label for the source IP **/
>>>>>>> +	hostsp = smack_host_label(sin);
>>>>>>> +
>>>>>>> +	if (hostsp == NULL) {
>>>>>>> +		if (ssp->smk_labeled != SMACK_CIPSO_SOCKET)
>>>>>>> +			smack_netlabel(newsock->sk, SMACK_CIPSO_SOCKET);
>>>>>>> +		return;
>>>>>>> +	}
>>>>>>> +	if (ssp->smk_labeled != SMACK_UNLABELED_SOCKET)
>>>>>>> +		smack_netlabel(newsock->sk, SMACK_UNLABELED_SOCKET);
>>>>>>> +	return;
>>>>>>> +}
>>>>>> NAK, you can't ignore return values like that.
>>>>>>
>>>>>> I'm sorry I didn't get a chance to respond to your email from this
>>>>>> morning, but the problem with the post_accept() hook is that you
>>>>>> can't fail in this hook.  There has been a _lot_ of discussion about
>>>>>> this over the past couple of years on the LSM list.  You should check
>>>>>> the archives for all the details but the main problem is that the
>>>>>> post_accept() hook is too late to deny the incoming connection so you
>>>>>> can't reject the connection at that point in any sane manner.
>>>>> well, i don't want to reject the connection here :)
>>>>>
>>>>>> I think I'm going to draft a patch to remove the post_accept()
>>>>>> hook since no one in-tree is using it and it's existence seems to
>>>>>> cause more problems than it solves.
>>>>>>
>>>>>> Now, I understand that your patch doesn't actually enforce any access
>>>>>> controls but it does call smack_netlabel() in several places and that
>>>>>> function can fail
>>>>> The smack_netlabel(newsock->sk, SMACK_CIPSO_SOCKET) can failed, but
>>>>> has no interest in this function (because the socket has already be
>>>>> SMACK_CIPSO_SOCKET labeled by the policy) I can remove it.
>>>>>
>>>>> but smack_netlabel(SMACK_UNLABELED_SOCKET) cannot fail, and that's
>>>>> what i'm interested in could this make the patch acceptable?
>>>> Please elaborate a bit more on how you would intend a user to configure
>>>> and make use of this.  Also, in what cases would you remove the
>>>> NetLabel from a socket?  What cases would you keep it?
>>> well, i think it is simple : let's say i want to run a "smack-labelled
>>> server" (apache, vsftpd, ...) clients connect from internet,  so the
>>> server admin/user  will want to add a "0.0.0.0/0 @" entry in netlabel
>>> that will _fail_ because the server will send back "labeled" packets.
>> I had to go back and look at the address based labeling patches, I had
>> somehow forgotten that the single label support in Smack can only be used
>> for removing labels, not adding them.  With that in mind your approach
>> should work although you will still get really bizarre behavior in the
>> following case:
>>
>>  * Service not running at the ambient label
>>  * Only address based label loaded into Smack is "0.0.0.0/0 @" (everything
>>    unlabeled)
>>  * Client connects to service using labeled networking
>>
>> If you and Casey can live with labeled connection suddenly becoming
>> unlabeled (I doubt the remote host will deal with it very gracefully) then
>> go for it.
> 
> The more I thought about this last night the more it bothered me so I decided 
> to take a quick look to see if I could come up with something that would let 
> me sleep easier.  The patch below is likely whitespace mangled and probably 
> won't apply cleanly but since I haven't done any testing I consider that a 
> good thing.

Hi Paul,
sorry for the trouble. I'll do some testing of your patch
I guess you're right, you're approach seems more complete

thanks
Etienne

> 
> Take a look at the patch below and see if it accomplishes what you want/need; 
> I think this is a much better approach than the socket_post_accept() method.
> 
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index 0278bc0..6419e83 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -20,6 +20,7 @@
>  #include <linux/ext2_fs.h>
>  #include <linux/kd.h>
>  #include <asm/ioctls.h>
> +#include <linux/ip.h>
>  #include <linux/tcp.h>
>  #include <linux/udp.h>
>  #include <linux/mutex.h>
> @@ -2559,21 +2560,40 @@ static void smack_sock_graft(struct sock *sk, struct 
> socket *parent)
>  static int smack_inet_conn_request(struct sock *sk, struct sk_buff *skb,
>  				   struct request_sock *req)
>  {
> +	u16 family = sk->sk_family;
>  	struct netlbl_lsm_secattr skb_secattr;
>  	struct socket_smack *ssp = sk->sk_security;
>  	char smack[SMK_LABELLEN];
>  	int rc;
>  
> -	if (skb == NULL)
> -		return -EACCES;
> +	/* handle mapped IPv4 packets arriving via IPv6 sockets */
> +	if (family == PF_INET6 && skb->protocol == htons(ETH_P_IP))
> +		family = PF_INET;
>  
>  	netlbl_secattr_init(&skb_secattr);
> +	
>  	rc = netlbl_skbuff_getattr(skb, sk->sk_family, &skb_secattr);
> -	if (rc == 0)
> +	if (rc == 0) {
> +		if (family == PF_INET &&
> +		    skb_secattr.type != NETLBL_NLTYPE_UNLABELED) {
> +			struct iphdr *hdr = ip_hdr(skb);
> +			struct sockaddr_in addr;
> +			
> +			/* if we are going to treat the other side of this
> +			 * connection as a single label, unlabeled host we
> +			 * shouldn't allow it to initiate a labeled
> +			 * connection because we will end up confusing
> +			 * everyone when we suddenly drop the labeling later */
> +			addr.sin_addr.s_addr = hdr->saddr;
> +			if (smack_host_label(&addr) != NULL) {
> +				rc = -EACCES;
> +				goto inet_conn_request_return;
> +			}
> +		}
>  		smack_from_secattr(&skb_secattr, smack);
> -	else
> +	} else
>  		strncpy(smack, smack_known_huh.smk_known, SMK_MAXLEN);
> -	netlbl_secattr_destroy(&skb_secattr);
> +
>  	/*
>  	 * Receiving a packet requires that the other end
>  	 * be able to write here. Read access is not required.
> @@ -2585,9 +2605,45 @@ static int smack_inet_conn_request(struct sock *sk, 
>  	if (rc == 0)
>  		strncpy(ssp->smk_packet, smack, SMK_MAXLEN);
>  
> +inet_conn_request_return:
> +	netlbl_secattr_destroy(&skb_secattr);
>  	return rc;
>  }
>
> +/**
> + * smack_inet_conn_established - Setup a new inbound connection
> + * @sk: the new child socket
> + * @skb: the inbound packet
> + *
> + * Perform the setup of a new inbound stream connection; this basically means
> + * check to see if the other end of the connection is configured as a single
> + * or multi-label host and enure the new connection's socket is configured
> + * correctly.
> + */
> +static void smack_inet_conn_established(struct sock *sk, struct sk_buff *skb)
> +{
> +	struct iphdr *hdr;
> +	struct sockaddr_in addr;
> +
> +	/* we only need to bother with IPv4 since we don't do IPv6 labeling */
> +	if (skb->protocol != htons(ETH_P_IP))
> +		return;
> +
> +	hdr = ip_hdr(skb);
> +	addr.sin_addr.s_addr = hdr->saddr;
> +	if (smack_host_label(&addr) == NULL)
> +		return;
> +
> +	/* the other end of this connection is configured as a single label,
> +	 * unlabeled host so we need to make sure we aren't going to label
> +	 * the socket */
> +	/* NOTE: this is _very_ important - we can only _remove_ the label at
> +	 * this point, trying to add a label to the socket here could result
> +	 * in a failure which we can't safely catch here due to the inability
> +	 * to signal an error */
> +	smack_netlabel(sk, SMACK_UNLABELED_SOCKET);
> +}
> +
>  /*
>   * Key management security hooks
>   *
> @@ -2940,6 +2996,7 @@ struct security_operations smack_ops = {
>  	.sk_free_security = 		smack_sk_free_security,
>  	.sock_graft = 			smack_sock_graft,
>  	.inet_conn_request = 		smack_inet_conn_request,
> +	.inet_conn_established =	smack_inet_conn_established,
>  
>   /* key management security hooks */
>  #ifdef CONFIG_KEYS
> 

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