[LSM-IPSec]: Security association restriction.

This patch series implements per packet access control via the
extension of the Linux Security Modules (LSM) interface by hooks in
the XFRM and pfkey subsystems that leverage IPSec security
associations to label packets.  Extensions to the SELinux LSM are
included that leverage the patch for this purpose.

This patch implements the changes necessary to the XFRM subsystem,
pfkey interface, ipv4/ipv6, and xfrm_user interface to restrict a
socket to use only authorized security associations (or no security
association) to send/receive network packets.

Patch purpose:

The patch is designed to enable access control per packets based on
the strongly authenticated IPSec security association.  Such access
controls augment the existing ones based on network interface and IP
address.  The former are very coarse-grained, and the latter can be
spoofed.  By using IPSec, the system can control access to remote
hosts based on cryptographic keys generated using the IPSec mechanism.
This enables access control on a per-machine basis or per-application
if the remote machine is running the same mechanism and trusted to
enforce the access control policy.

Patch design approach:

The overall approach is that policy (xfrm_policy) entries set by
user-level programs (e.g., setkey for ipsec-tools) are extended with a
security context that is used at policy selection time in the XFRM
subsystem to restrict the sockets that can send/receive packets via
security associations (xfrm_states) that are built from those
policies.

A presentation available at
www.selinux-symposium.org/2005/presentations/session2/2-3-jaeger.pdf
from the SELinux symposium describes the overall approach.

Patch implementation details:

On output, the policy retrieved (via xfrm_policy_lookup or
xfrm_sk_policy_lookup) must be authorized for the security context of
the socket and the same security context is required for resultant
security association (retrieved or negotiated via racoon in
ipsec-tools).  This is enforced in xfrm_state_find.

On input, the policy retrieved must also be authorized for the socket
(at __xfrm_policy_check), and the security context of the policy must
also match the security association being used.

The patch has virtually no impact on packets that do not use IPSec.
The existing Netfilter (outgoing) and LSM rcv_skb hooks are used as
before.

Also, if IPSec is used without security contexts, the impact is
minimal.  The LSM must allow such policies to be selected for the
combination of socket and remote machine, but subsequent IPSec
processing proceeds as in the original case.

Testing:

The pfkey interface is tested using the ipsec-tools.  ipsec-tools have
been modified (a separate ipsec-tools patch is available for version
0.5) that supports assignment of xfrm_policy entries and security
associations with security contexts via setkey and the negotiation
using the security contexts via racoon.

The xfrm_user interface is tested via ad hoc programs that set
security contexts.  These programs are also available from me, and
contain programs for setting, getting, and deleting policy for testing
this interface.  Testing of sa functions was done by tracing kernel
behavior.

Signed-off-by: Trent Jaeger <tjaeger@cse.psu.edu>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 141 insertions, 7 deletions

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index 0cdd9a0..92e2b80 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -7,7 +7,7 @@
  * 	Kazunori MIYAZAWA @USAGI
  * 	Kunihiro Ishiguro <kunihiro@ipinfusion.com>
  * 		IPv6 support
- * 	
+ *
  */
 
 #include <linux/module.h>
@@ -88,6 +88,34 @@ static int verify_encap_tmpl(struct rtattr **xfrma)
 	return 0;
 }
 
+
+static inline int verify_sec_ctx_len(struct rtattr **xfrma)
+{
+	struct rtattr *rt = xfrma[XFRMA_SEC_CTX - 1];
+	struct xfrm_user_sec_ctx *uctx;
+	int len = 0;
+
+	if (!rt)
+		return 0;
+
+	if (rt->rta_len < sizeof(*uctx))
+		return -EINVAL;
+
+	uctx = RTA_DATA(rt);
+
+	if (uctx->ctx_len > PAGE_SIZE)
+		return -EINVAL;
+
+	len += sizeof(struct xfrm_user_sec_ctx);
+	len += uctx->ctx_len;
+
+	if (uctx->len != len)
+		return -EINVAL;
+
+	return 0;
+}
+
+
 static int verify_newsa_info(struct xfrm_usersa_info *p,
 			     struct rtattr **xfrma)
 {
@@ -145,6 +173,8 @@ static int verify_newsa_info(struct xfrm_usersa_info *p,
 		goto out;
 	if ((err = verify_encap_tmpl(xfrma)))
 		goto out;
+	if ((err = verify_sec_ctx_len(xfrma)))
+		goto out;
 
 	err = -EINVAL;
 	switch (p->mode) {
@@ -209,6 +239,30 @@ static int attach_encap_tmpl(struct xfrm_encap_tmpl **encapp, struct rtattr *u_a
 	return 0;
 }
 
+
+static inline int xfrm_user_sec_ctx_size(struct xfrm_policy *xp)
+{
+	struct xfrm_sec_ctx *xfrm_ctx = xp->security;
+	int len = 0;
+
+	if (xfrm_ctx) {
+		len += sizeof(struct xfrm_user_sec_ctx);
+		len += xfrm_ctx->ctx_len;
+	}
+	return len;
+}
+
+static int attach_sec_ctx(struct xfrm_state *x, struct rtattr *u_arg)
+{
+	struct xfrm_user_sec_ctx *uctx;
+
+	if (!u_arg)
+		return 0;
+
+	uctx = RTA_DATA(u_arg);
+	return security_xfrm_state_alloc(x, uctx);
+}
+
 static void copy_from_user_state(struct xfrm_state *x, struct xfrm_usersa_info *p)
 {
 	memcpy(&x->id, &p->id, sizeof(x->id));
@@ -253,6 +307,9 @@ static struct xfrm_state *xfrm_state_construct(struct xfrm_usersa_info *p,
 	if (err)
 		goto error;
 
+	if ((err = attach_sec_ctx(x, xfrma[XFRMA_SEC_CTX-1])))
+		goto error;
+
 	x->km.seq = p->seq;
 
 	return x;
@@ -272,11 +329,11 @@ static int xfrm_add_sa(struct sk_buff *skb, struct nlmsghdr *nlh, void **xfrma)
 	int err;
 	struct km_event c;
 
-	err = verify_newsa_info(p, (struct rtattr **) xfrma);
+	err = verify_newsa_info(p, (struct rtattr **)xfrma);
 	if (err)
 		return err;
 
-	x = xfrm_state_construct(p, (struct rtattr **) xfrma, &err);
+	x = xfrm_state_construct(p, (struct rtattr **)xfrma, &err);
 	if (!x)
 		return err;
 
@@ -390,6 +447,19 @@ static int dump_one_state(struct xfrm_state *x, int count, void *ptr)
 	if (x->encap)
 		RTA_PUT(skb, XFRMA_ENCAP, sizeof(*x->encap), x->encap);
 
+	if (x->security) {
+		int ctx_size = sizeof(struct xfrm_sec_ctx) +
+				x->security->ctx_len;
+		struct rtattr *rt = __RTA_PUT(skb, XFRMA_SEC_CTX, ctx_size);
+		struct xfrm_user_sec_ctx *uctx = RTA_DATA(rt);
+
+		uctx->exttype = XFRMA_SEC_CTX;
+		uctx->len = ctx_size;
+		uctx->ctx_doi = x->security->ctx_doi;
+		uctx->ctx_alg = x->security->ctx_alg;
+		uctx->ctx_len = x->security->ctx_len;
+		memcpy(uctx + 1, x->security->ctx_str, x->security->ctx_len);
+	}
 	nlh->nlmsg_len = skb->tail - b;
 out:
 	sp->this_idx++;
@@ -603,6 +673,18 @@ static int verify_newpolicy_info(struct xfrm_userpolicy_info *p)
 	return verify_policy_dir(p->dir);
 }
 
+static int copy_from_user_sec_ctx(struct xfrm_policy *pol, struct rtattr **xfrma)
+{
+	struct rtattr *rt = xfrma[XFRMA_SEC_CTX-1];
+	struct xfrm_user_sec_ctx *uctx;
+
+	if (!rt)
+		return 0;
+
+	uctx = RTA_DATA(rt);
+	return security_xfrm_policy_alloc(pol, uctx);
+}
+
 static void copy_templates(struct xfrm_policy *xp, struct xfrm_user_tmpl *ut,
 			   int nr)
 {
@@ -681,7 +763,10 @@ static struct xfrm_policy *xfrm_policy_construct(struct xfrm_userpolicy_info *p,
 	}
 
 	copy_from_user_policy(xp, p);
-	err = copy_from_user_tmpl(xp, xfrma);
+
+	if (!(err = copy_from_user_tmpl(xp, xfrma)))
+		err = copy_from_user_sec_ctx(xp, xfrma);
+
 	if (err) {
 		*errp = err;
 		kfree(xp);
@@ -702,8 +787,11 @@ static int xfrm_add_policy(struct sk_buff *skb, struct nlmsghdr *nlh, void **xfr
 	err = verify_newpolicy_info(p);
 	if (err)
 		return err;
+	err = verify_sec_ctx_len((struct rtattr **)xfrma);
+	if (err)
+		return err;
 
-	xp = xfrm_policy_construct(p, (struct rtattr **) xfrma, &err);
+	xp = xfrm_policy_construct(p, (struct rtattr **)xfrma, &err);
 	if (!xp)
 		return err;
 
@@ -761,6 +849,27 @@ rtattr_failure:
 	return -1;
 }
 
+static int copy_to_user_sec_ctx(struct xfrm_policy *xp, struct sk_buff *skb)
+{
+	if (xp->security) {
+		int ctx_size = sizeof(struct xfrm_sec_ctx) +
+				xp->security->ctx_len;
+		struct rtattr *rt = __RTA_PUT(skb, XFRMA_SEC_CTX, ctx_size);
+		struct xfrm_user_sec_ctx *uctx = RTA_DATA(rt);
+
+		uctx->exttype = XFRMA_SEC_CTX;
+		uctx->len = ctx_size;
+		uctx->ctx_doi = xp->security->ctx_doi;
+		uctx->ctx_alg = xp->security->ctx_alg;
+		uctx->ctx_len = xp->security->ctx_len;
+		memcpy(uctx + 1, xp->security->ctx_str, xp->security->ctx_len);
+	}
+	return 0;
+
+ rtattr_failure:
+	return -1;
+}
+
 static int dump_one_policy(struct xfrm_policy *xp, int dir, int count, void *ptr)
 {
 	struct xfrm_dump_info *sp = ptr;
@@ -782,6 +891,8 @@ static int dump_one_policy(struct xfrm_policy *xp, int dir, int count, void *ptr
 	copy_to_user_policy(xp, p, dir);
 	if (copy_to_user_tmpl(xp, skb) < 0)
 		goto nlmsg_failure;
+	if (copy_to_user_sec_ctx(xp, skb))
+		goto nlmsg_failure;
 
 	nlh->nlmsg_len = skb->tail - b;
 out:
@@ -852,8 +963,25 @@ static int xfrm_get_policy(struct sk_buff *skb, struct nlmsghdr *nlh, void **xfr
 
 	if (p->index)
 		xp = xfrm_policy_byid(p->dir, p->index, delete);
-	else
-		xp = xfrm_policy_bysel(p->dir, &p->sel, delete);
+	else {
+		struct rtattr **rtattrs = (struct rtattr **)xfrma;
+		struct rtattr *rt = rtattrs[XFRMA_SEC_CTX-1];
+		struct xfrm_policy tmp;
+
+		err = verify_sec_ctx_len(rtattrs);
+		if (err)
+			return err;
+
+		memset(&tmp, 0, sizeof(struct xfrm_policy));
+		if (rt) {
+			struct xfrm_user_sec_ctx *uctx = RTA_DATA(rt);
+
+			if ((err = security_xfrm_policy_alloc(&tmp, uctx)))
+				return err;
+		}
+		xp = xfrm_policy_bysel_ctx(p->dir, &p->sel, tmp.security, delete);
+		security_xfrm_policy_free(&tmp);
+	}
 	if (xp == NULL)
 		return -ENOENT;
 
@@ -1224,6 +1352,8 @@ static int build_acquire(struct sk_buff *skb, struct xfrm_state *x,
 
 	if (copy_to_user_tmpl(xp, skb) < 0)
 		goto nlmsg_failure;
+	if (copy_to_user_sec_ctx(xp, skb))
+		goto nlmsg_failure;
 
 	nlh->nlmsg_len = skb->tail - b;
 	return skb->len;
@@ -1241,6 +1371,7 @@ static int xfrm_send_acquire(struct xfrm_state *x, struct xfrm_tmpl *xt,
 
 	len = RTA_SPACE(sizeof(struct xfrm_user_tmpl) * xp->xfrm_nr);
 	len += NLMSG_SPACE(sizeof(struct xfrm_user_acquire));
+	len += RTA_SPACE(xfrm_user_sec_ctx_size(xp));
 	skb = alloc_skb(len, GFP_ATOMIC);
 	if (skb == NULL)
 		return -ENOMEM;
@@ -1324,6 +1455,8 @@ static int build_polexpire(struct sk_buff *skb, struct xfrm_policy *xp,
 	copy_to_user_policy(xp, &upe->pol, dir);
 	if (copy_to_user_tmpl(xp, skb) < 0)
 		goto nlmsg_failure;
+	if (copy_to_user_sec_ctx(xp, skb))
+		goto nlmsg_failure;
 	upe->hard = !!hard;
 
 	nlh->nlmsg_len = skb->tail - b;
@@ -1341,6 +1474,7 @@ static int xfrm_exp_policy_notify(struct xfrm_policy *xp, int dir, struct km_eve
 
 	len = RTA_SPACE(sizeof(struct xfrm_user_tmpl) * xp->xfrm_nr);
 	len += NLMSG_SPACE(sizeof(struct xfrm_user_polexpire));
+	len += RTA_SPACE(xfrm_user_sec_ctx_size(xp));
 	skb = alloc_skb(len, GFP_ATOMIC);
 	if (skb == NULL)
 		return -ENOMEM;