netlabel: Add functionality to set the security attributes of a packet

This patch builds upon the new NetLabel address selector functionality by
providing the NetLabel KAPI and CIPSO engine support needed to enable the
new packet-based labeling.  The only new addition to the NetLabel KAPI at
this point is shown below:

 * int netlbl_skbuff_setattr(skb, family, secattr)

... and is designed to be called from a Netfilter hook after the packet's
IP header has been populated such as in the FORWARD or LOCAL_OUT hooks.

This patch also provides the necessary SELinux hooks to support this new
functionality.  Smack support is not currently included due to uncertainty
regarding the permissions needed to expand the Smack network access controls.

Signed-off-by: Paul Moore <paul.moore@hp.com>
Reviewed-by: James Morris <jmorris@namei.org>

1 files changed, 183 insertions, 39 deletions

diff --git a/net/ipv4/cipso_ipv4.c b/net/ipv4/cipso_ipv4.c
index bf87eddfec30..e13d6dbb66ab 100644
--- a/net/ipv4/cipso_ipv4.c
+++ b/net/ipv4/cipso_ipv4.c
@@ -13,7 +13,7 @@
  */
 
 /*
- * (c) Copyright Hewlett-Packard Development Company, L.P., 2006
+ * (c) Copyright Hewlett-Packard Development Company, L.P., 2006, 2008
  *
  * This program is free software;  you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -1665,48 +1665,27 @@ void cipso_v4_error(struct sk_buff *skb, int error, u32 gateway)
 }
 
 /**
- * cipso_v4_sock_setattr - Add a CIPSO option to a socket
- * @sk: the socket
+ * cipso_v4_genopt - Generate a CIPSO option
+ * @buf: the option buffer
+ * @buf_len: the size of opt_buf
  * @doi_def: the CIPSO DOI to use
- * @secattr: the specific security attributes of the socket
+ * @secattr: the security attributes
  *
  * Description:
- * Set the CIPSO option on the given socket using the DOI definition and
- * security attributes passed to the function.  This function requires
- * exclusive access to @sk, which means it either needs to be in the
- * process of being created or locked.  Returns zero on success and negative
- * values on failure.
+ * Generate a CIPSO option using the DOI definition and security attributes
+ * passed to the function.  Returns the length of the option on success and
+ * negative values on failure.
  *
  */
-int cipso_v4_sock_setattr(struct sock *sk,
-			  const struct cipso_v4_doi *doi_def,
-			  const struct netlbl_lsm_secattr *secattr)
+static int cipso_v4_genopt(unsigned char *buf, u32 buf_len,
+			   const struct cipso_v4_doi *doi_def,
+			   const struct netlbl_lsm_secattr *secattr)
 {
-	int ret_val = -EPERM;
+	int ret_val;
 	u32 iter;
-	unsigned char *buf;
-	u32 buf_len = 0;
-	u32 opt_len;
-	struct ip_options *opt = NULL;
-	struct inet_sock *sk_inet;
-	struct inet_connection_sock *sk_conn;
-
-	/* In the case of sock_create_lite(), the sock->sk field is not
-	 * defined yet but it is not a problem as the only users of these
-	 * "lite" PF_INET sockets are functions which do an accept() call
-	 * afterwards so we will label the socket as part of the accept(). */
-	if (sk == NULL)
-		return 0;
 
-	/* We allocate the maximum CIPSO option size here so we are probably
-	 * being a little wasteful, but it makes our life _much_ easier later
-	 * on and after all we are only talking about 40 bytes. */
-	buf_len = CIPSO_V4_OPT_LEN_MAX;
-	buf = kmalloc(buf_len, GFP_ATOMIC);
-	if (buf == NULL) {
-		ret_val = -ENOMEM;
-		goto socket_setattr_failure;
-	}
+	if (buf_len <= CIPSO_V4_HDR_LEN)
+		return -ENOSPC;
 
 	/* XXX - This code assumes only one tag per CIPSO option which isn't
 	 * really a good assumption to make but since we only support the MAC
@@ -1734,8 +1713,7 @@ int cipso_v4_sock_setattr(struct sock *sk,
 						   buf_len - CIPSO_V4_HDR_LEN);
 			break;
 		default:
-			ret_val = -EPERM;
-			goto socket_setattr_failure;
+			return -EPERM;
 		}
 
 		iter++;
@@ -1743,9 +1721,58 @@ int cipso_v4_sock_setattr(struct sock *sk,
 		 iter < CIPSO_V4_TAG_MAXCNT &&
 		 doi_def->tags[iter] != CIPSO_V4_TAG_INVALID);
 	if (ret_val < 0)
-		goto socket_setattr_failure;
+		return ret_val;
 	cipso_v4_gentag_hdr(doi_def, buf, ret_val);
-	buf_len = CIPSO_V4_HDR_LEN + ret_val;
+	return CIPSO_V4_HDR_LEN + ret_val;
+}
+
+/**
+ * cipso_v4_sock_setattr - Add a CIPSO option to a socket
+ * @sk: the socket
+ * @doi_def: the CIPSO DOI to use
+ * @secattr: the specific security attributes of the socket
+ *
+ * Description:
+ * Set the CIPSO option on the given socket using the DOI definition and
+ * security attributes passed to the function.  This function requires
+ * exclusive access to @sk, which means it either needs to be in the
+ * process of being created or locked.  Returns zero on success and negative
+ * values on failure.
+ *
+ */
+int cipso_v4_sock_setattr(struct sock *sk,
+			  const struct cipso_v4_doi *doi_def,
+			  const struct netlbl_lsm_secattr *secattr)
+{
+	int ret_val = -EPERM;
+	unsigned char *buf = NULL;
+	u32 buf_len;
+	u32 opt_len;
+	struct ip_options *opt = NULL;
+	struct inet_sock *sk_inet;
+	struct inet_connection_sock *sk_conn;
+
+	/* In the case of sock_create_lite(), the sock->sk field is not
+	 * defined yet but it is not a problem as the only users of these
+	 * "lite" PF_INET sockets are functions which do an accept() call
+	 * afterwards so we will label the socket as part of the accept(). */
+	if (sk == NULL)
+		return 0;
+
+	/* We allocate the maximum CIPSO option size here so we are probably
+	 * being a little wasteful, but it makes our life _much_ easier later
+	 * on and after all we are only talking about 40 bytes. */
+	buf_len = CIPSO_V4_OPT_LEN_MAX;
+	buf = kmalloc(buf_len, GFP_ATOMIC);
+	if (buf == NULL) {
+		ret_val = -ENOMEM;
+		goto socket_setattr_failure;
+	}
+
+	ret_val = cipso_v4_genopt(buf, buf_len, doi_def, secattr);
+	if (ret_val < 0)
+		goto socket_setattr_failure;
+	buf_len = ret_val;
 
 	/* We can't use ip_options_get() directly because it makes a call to
 	 * ip_options_get_alloc() which allocates memory with GFP_KERNEL and
@@ -1854,6 +1881,123 @@ int cipso_v4_sock_getattr(struct sock *sk, struct netlbl_lsm_secattr *secattr)
 }
 
 /**
+ * cipso_v4_skbuff_setattr - Set the CIPSO option on a packet
+ * @skb: the packet
+ * @secattr: the security attributes
+ *
+ * Description:
+ * Set the CIPSO option on the given packet based on the security attributes.
+ * Returns a pointer to the IP header on success and NULL on failure.
+ *
+ */
+int cipso_v4_skbuff_setattr(struct sk_buff *skb,
+			    const struct cipso_v4_doi *doi_def,
+			    const struct netlbl_lsm_secattr *secattr)
+{
+	int ret_val;
+	struct iphdr *iph;
+	struct ip_options *opt = &IPCB(skb)->opt;
+	unsigned char buf[CIPSO_V4_OPT_LEN_MAX];
+	u32 buf_len = CIPSO_V4_OPT_LEN_MAX;
+	u32 opt_len;
+	int len_delta;
+
+	buf_len = cipso_v4_genopt(buf, buf_len, doi_def, secattr);
+	if (buf_len < 0)
+		return buf_len;
+	opt_len = (buf_len + 3) & ~3;
+
+	/* we overwrite any existing options to ensure that we have enough
+	 * room for the CIPSO option, the reason is that we _need_ to guarantee
+	 * that the security label is applied to the packet - we do the same
+	 * thing when using the socket options and it hasn't caused a problem,
+	 * if we need to we can always revisit this choice later */
+
+	len_delta = opt_len - opt->optlen;
+	/* if we don't ensure enough headroom we could panic on the skb_push()
+	 * call below so make sure we have enough, we are also "mangling" the
+	 * packet so we should probably do a copy-on-write call anyway */
+	ret_val = skb_cow(skb, skb_headroom(skb) + len_delta);
+	if (ret_val < 0)
+		return ret_val;
+
+	if (len_delta > 0) {
+		/* we assume that the header + opt->optlen have already been
+		 * "pushed" in ip_options_build() or similar */
+		iph = ip_hdr(skb);
+		skb_push(skb, len_delta);
+		memmove((char *)iph - len_delta, iph, iph->ihl << 2);
+		skb_reset_network_header(skb);
+		iph = ip_hdr(skb);
+	} else if (len_delta < 0) {
+		iph = ip_hdr(skb);
+		memset(iph + 1, IPOPT_NOP, opt->optlen);
+	} else
+		iph = ip_hdr(skb);
+
+	if (opt->optlen > 0)
+		memset(opt, 0, sizeof(*opt));
+	opt->optlen = opt_len;
+	opt->cipso = sizeof(struct iphdr);
+	opt->is_changed = 1;
+
+	/* we have to do the following because we are being called from a
+	 * netfilter hook which means the packet already has had the header
+	 * fields populated and the checksum calculated - yes this means we
+	 * are doing more work than needed but we do it to keep the core
+	 * stack clean and tidy */
+	memcpy(iph + 1, buf, buf_len);
+	if (opt_len > buf_len)
+		memset((char *)(iph + 1) + buf_len, 0, opt_len - buf_len);
+	if (len_delta != 0) {
+		iph->ihl = 5 + (opt_len >> 2);
+		iph->tot_len = htons(skb->len);
+	}
+	ip_send_check(iph);
+
+	return 0;
+}
+
+/**
+ * cipso_v4_skbuff_delattr - Delete any CIPSO options from a packet
+ * @skb: the packet
+ *
+ * Description:
+ * Removes any and all CIPSO options from the given packet.  Returns zero on
+ * success, negative values on failure.
+ *
+ */
+int cipso_v4_skbuff_delattr(struct sk_buff *skb)
+{
+	int ret_val;
+	struct iphdr *iph;
+	struct ip_options *opt = &IPCB(skb)->opt;
+	unsigned char *cipso_ptr;
+
+	if (opt->cipso == 0)
+		return 0;
+
+	/* since we are changing the packet we should make a copy */
+	ret_val = skb_cow(skb, skb_headroom(skb));
+	if (ret_val < 0)
+		return ret_val;
+
+	/* the easiest thing to do is just replace the cipso option with noop
+	 * options since we don't change the size of the packet, although we
+	 * still need to recalculate the checksum */
+
+	iph = ip_hdr(skb);
+	cipso_ptr = (unsigned char *)iph + opt->cipso;
+	memset(cipso_ptr, IPOPT_NOOP, cipso_ptr[1]);
+	opt->cipso = 0;
+	opt->is_changed = 1;
+
+	ip_send_check(iph);
+
+	return 0;
+}
+
+/**
  * cipso_v4_skbuff_getattr - Get the security attributes from the CIPSO option
  * @skb: the packet
  * @secattr: the security attributes