[LSM-IPSec]: Per-packet access control.

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 SELinux LSM to
create, deallocate, and use security contexts for policies
(xfrm_policy) and security associations (xfrm_state) that enable
control of a socket's ability to send and receive packets.

Patch purpose:

The patch is designed to enable the SELinux LSM to implement access
control on individual packets based on the strongly authenticated
IPSec security association.  Such access controls augment the existing
ones in SELinux based on network interface and IP address.  The former
are very coarse-grained, and the latter can be spoofed.  By using
IPSec, the SELinux 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 patch's main function is to authorize a socket's access to a IPSec
policy based on their security contexts.  Since the communication is
implemented by a security association, the patch ensures that the
security association's negotiated and used have the same security
context.  The patch enables allocation and deallocation of such
security contexts for policies and security associations.  It also
enables copying of the security context when policies are cloned.
Lastly, the patch ensures that packets that are sent without using a
IPSec security assocation with a security context are allowed to be
sent in that manner.

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:

The function which authorizes a socket to perform a requested
operation (send/receive) on a IPSec policy (xfrm_policy) is
selinux_xfrm_policy_lookup.  The Netfilter and rcv_skb hooks ensure
that if a IPSec SA with a securit y association has not been used,
then the socket is allowed to send or receive the packet,
respectively.

The patch implements SELinux function for allocating security contexts
when policies (xfrm_policy) are created via the pfkey or xfrm_user
interfaces via selinux_xfrm_policy_alloc.  When a security association
is built, SELinux allocates the security context designated by the
XFRM subsystem which is based on that of the authorized policy via
selinux_xfrm_state_alloc.

When a xfrm_policy is cloned, the security context of that policy, if
any, is copied to the clone via selinux_xfrm_policy_clone.

When a xfrm_policy or xfrm_state is freed, its security context, if
any is also freed at selinux_xfrm_policy_free or
selinux_xfrm_state_free.

Testing:

The SELinux authorization function is tested using ipsec-tools.  We
created policies and security associations with particular security
contexts and added SELinux access control policy entries to verify the
authorization decision.  We also made sure that packets for which no
security context was supplied (which either did or did not use
security associations) were authorized using an unlabelled context.

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, 311 insertions, 0 deletions

diff --git a/security/selinux/xfrm.c b/security/selinux/xfrm.c
new file mode 100644
index 000000000000..c4d87d4dca7b
--- /dev/null
+++ b/security/selinux/xfrm.c
@@ -0,0 +1,311 @@
+/*
+ *  NSA Security-Enhanced Linux (SELinux) security module
+ *
+ *  This file contains the SELinux XFRM hook function implementations.
+ *
+ *  Authors:  Serge Hallyn <sergeh@us.ibm.com>
+ *	      Trent Jaeger <jaegert@us.ibm.com>
+ *
+ *  Copyright (C) 2005 International Business Machines Corporation
+ *
+ *	This program is free software; you can redistribute it and/or modify
+ *	it under the terms of the GNU General Public License version 2,
+ *	as published by the Free Software Foundation.
+ */
+
+/*
+ * USAGE:
+ * NOTES:
+ *   1. Make sure to enable the following options in your kernel config:
+ *	CONFIG_SECURITY=y
+ *	CONFIG_SECURITY_NETWORK=y
+ *	CONFIG_SECURITY_NETWORK_XFRM=y
+ *	CONFIG_SECURITY_SELINUX=m/y
+ * ISSUES:
+ *   1. Caching packets, so they are not dropped during negotiation
+ *   2. Emulating a reasonable SO_PEERSEC across machines
+ *   3. Testing addition of sk_policy's with security context via setsockopt
+ */
+#include <linux/config.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/security.h>
+#include <linux/types.h>
+#include <linux/netfilter.h>
+#include <linux/netfilter_ipv4.h>
+#include <linux/netfilter_ipv6.h>
+#include <linux/ip.h>
+#include <linux/tcp.h>
+#include <linux/skbuff.h>
+#include <linux/xfrm.h>
+#include <net/xfrm.h>
+#include <net/checksum.h>
+#include <net/udp.h>
+#include <asm/semaphore.h>
+
+#include "avc.h"
+#include "objsec.h"
+#include "xfrm.h"
+
+
+/*
+ * Returns true if an LSM/SELinux context
+ */
+static inline int selinux_authorizable_ctx(struct xfrm_sec_ctx *ctx)
+{
+	return (ctx &&
+		(ctx->ctx_doi == XFRM_SC_DOI_LSM) &&
+		(ctx->ctx_alg == XFRM_SC_ALG_SELINUX));
+}
+
+/*
+ * Returns true if the xfrm contains a security blob for SELinux
+ */
+static inline int selinux_authorizable_xfrm(struct xfrm_state *x)
+{
+	return selinux_authorizable_ctx(x->security);
+}
+
+/*
+ * LSM hook implementation that authorizes that a socket can be used
+ * with the corresponding xfrm_sec_ctx and direction.
+ */
+int selinux_xfrm_policy_lookup(struct xfrm_policy *xp, u32 sk_sid, u8 dir)
+{
+	int rc = 0;
+	u32 sel_sid = SECINITSID_UNLABELED;
+	struct xfrm_sec_ctx *ctx;
+
+	/* Context sid is either set to label or ANY_ASSOC */
+	if ((ctx = xp->security)) {
+		if (!selinux_authorizable_ctx(ctx))
+			return -EINVAL;
+
+		sel_sid = ctx->ctx_sid;
+	}
+
+	rc = avc_has_perm(sk_sid, sel_sid, SECCLASS_ASSOCIATION,
+			  ((dir == FLOW_DIR_IN) ? ASSOCIATION__RECVFROM :
+			   ((dir == FLOW_DIR_OUT) ?  ASSOCIATION__SENDTO :
+			    (ASSOCIATION__SENDTO | ASSOCIATION__RECVFROM))),
+			  NULL);
+
+	return rc;
+}
+
+/*
+ * Security blob allocation for xfrm_policy and xfrm_state
+ * CTX does not have a meaningful value on input
+ */
+static int selinux_xfrm_sec_ctx_alloc(struct xfrm_sec_ctx **ctxp, struct xfrm_user_sec_ctx *uctx)
+{
+	int rc = 0;
+	struct task_security_struct *tsec = current->security;
+	struct xfrm_sec_ctx *ctx;
+
+	BUG_ON(!uctx);
+	BUG_ON(uctx->ctx_doi != XFRM_SC_ALG_SELINUX);
+
+	if (uctx->ctx_len >= PAGE_SIZE)
+		return -ENOMEM;
+
+	*ctxp = ctx = kmalloc(sizeof(*ctx) +
+			      uctx->ctx_len,
+			      GFP_KERNEL);
+
+	if (!ctx)
+		return -ENOMEM;
+
+	ctx->ctx_doi = uctx->ctx_doi;
+	ctx->ctx_len = uctx->ctx_len;
+	ctx->ctx_alg = uctx->ctx_alg;
+
+	memcpy(ctx->ctx_str,
+	       uctx+1,
+	       ctx->ctx_len);
+	rc = security_context_to_sid(ctx->ctx_str,
+				     ctx->ctx_len,
+				     &ctx->ctx_sid);
+
+	if (rc)
+		goto out;
+
+	/*
+	 * Does the subject have permission to set security or permission to
+	 * do the relabel?
+	 * Must be permitted to relabel from default socket type (process type)
+	 * to specified context
+	 */
+	rc = avc_has_perm(tsec->sid, tsec->sid,
+			  SECCLASS_ASSOCIATION,
+			  ASSOCIATION__RELABELFROM, NULL);
+	if (rc)
+		goto out;
+
+	rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
+			  SECCLASS_ASSOCIATION,
+			  ASSOCIATION__RELABELTO, NULL);
+	if (rc)
+		goto out;
+
+	return rc;
+
+out:
+	*ctxp = 0;
+	kfree(ctx);
+	return rc;
+}
+
+/*
+ * LSM hook implementation that allocs and transfers uctx spec to
+ * xfrm_policy.
+ */
+int selinux_xfrm_policy_alloc(struct xfrm_policy *xp, struct xfrm_user_sec_ctx *uctx)
+{
+	int err;
+
+	BUG_ON(!xp);
+
+	err = selinux_xfrm_sec_ctx_alloc(&xp->security, uctx);
+	return err;
+}
+
+
+/*
+ * LSM hook implementation that copies security data structure from old to
+ * new for policy cloning.
+ */
+int selinux_xfrm_policy_clone(struct xfrm_policy *old, struct xfrm_policy *new)
+{
+	struct xfrm_sec_ctx *old_ctx, *new_ctx;
+
+	old_ctx = old->security;
+
+	if (old_ctx) {
+		new_ctx = new->security = kmalloc(sizeof(*new_ctx) +
+						  old_ctx->ctx_len,
+						  GFP_KERNEL);
+
+		if (!new_ctx)
+			return -ENOMEM;
+
+		memcpy(new_ctx, old_ctx, sizeof(*new_ctx));
+		memcpy(new_ctx->ctx_str, old_ctx->ctx_str, new_ctx->ctx_len);
+	}
+	return 0;
+}
+
+/*
+ * LSM hook implementation that frees xfrm_policy security information.
+ */
+void selinux_xfrm_policy_free(struct xfrm_policy *xp)
+{
+	struct xfrm_sec_ctx *ctx = xp->security;
+	if (ctx)
+		kfree(ctx);
+}
+
+/*
+ * LSM hook implementation that allocs and transfers sec_ctx spec to
+ * xfrm_state.
+ */
+int selinux_xfrm_state_alloc(struct xfrm_state *x, struct xfrm_user_sec_ctx *uctx)
+{
+	int err;
+
+	BUG_ON(!x);
+
+	err = selinux_xfrm_sec_ctx_alloc(&x->security, uctx);
+	return err;
+}
+
+/*
+ * LSM hook implementation that frees xfrm_state security information.
+ */
+void selinux_xfrm_state_free(struct xfrm_state *x)
+{
+	struct xfrm_sec_ctx *ctx = x->security;
+	if (ctx)
+		kfree(ctx);
+}
+
+/*
+ * LSM hook that controls access to unlabelled packets.  If
+ * a xfrm_state is authorizable (defined by macro) then it was
+ * already authorized by the IPSec process.  If not, then
+ * we need to check for unlabelled access since this may not have
+ * gone thru the IPSec process.
+ */
+int selinux_xfrm_sock_rcv_skb(u32 isec_sid, struct sk_buff *skb)
+{
+	int i, rc = 0;
+	struct sec_path *sp;
+
+	sp = skb->sp;
+
+	if (sp) {
+		/*
+		 * __xfrm_policy_check does not approve unless xfrm_policy_ok
+		 * says that spi's match for policy and the socket.
+		 *
+		 *  Only need to verify the existence of an authorizable sp.
+		 */
+		for (i = 0; i < sp->len; i++) {
+			struct xfrm_state *x = sp->x[i].xvec;
+
+			if (x && selinux_authorizable_xfrm(x))
+				goto accept;
+		}
+	}
+
+	/* check SELinux sock for unlabelled access */
+	rc = avc_has_perm(isec_sid, SECINITSID_UNLABELED, SECCLASS_ASSOCIATION,
+			  ASSOCIATION__RECVFROM, NULL);
+	if (rc)
+		goto drop;
+
+accept:
+	return 0;
+
+drop:
+	return rc;
+}
+
+/*
+ * POSTROUTE_LAST hook's XFRM processing:
+ * If we have no security association, then we need to determine
+ * whether the socket is allowed to send to an unlabelled destination.
+ * If we do have a authorizable security association, then it has already been
+ * checked in xfrm_policy_lookup hook.
+ */
+int selinux_xfrm_postroute_last(u32 isec_sid, struct sk_buff *skb)
+{
+	struct dst_entry *dst;
+	int rc = 0;
+
+	dst = skb->dst;
+
+	if (dst) {
+		struct dst_entry *dst_test;
+
+		for (dst_test = dst; dst_test != 0;
+		     dst_test = dst_test->child) {
+			struct xfrm_state *x = dst_test->xfrm;
+
+			if (x && selinux_authorizable_xfrm(x))
+				goto accept;
+		}
+	}
+
+	rc = avc_has_perm(isec_sid, SECINITSID_UNLABELED, SECCLASS_ASSOCIATION,
+			  ASSOCIATION__SENDTO, NULL);
+	if (rc)
+		goto drop;
+
+accept:
+	return NF_ACCEPT;
+
+drop:
+	return NF_DROP;
+}