[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>

3 files changed, 173 insertions, 1 deletions

diff --git a/include/linux/pfkeyv2.h b/include/linux/pfkeyv2.h
index 724066778aff..6351c4055ace 100644
--- a/include/linux/pfkeyv2.h
+++ b/include/linux/pfkeyv2.h
@@ -216,6 +216,16 @@ struct sadb_x_nat_t_port {
 } __attribute__((packed));
 /* sizeof(struct sadb_x_nat_t_port) == 8 */
 
+/* Generic LSM security context */
+struct sadb_x_sec_ctx {
+        uint16_t        sadb_x_sec_len;
+        uint16_t        sadb_x_sec_exttype;
+        uint8_t         sadb_x_ctx_alg;  /* LSMs: e.g., selinux == 1 */
+        uint8_t         sadb_x_ctx_doi;
+        uint16_t        sadb_x_ctx_len;
+} __attribute__((packed));
+/* sizeof(struct sadb_sec_ctx) = 8 */
+
 /* Message types */
 #define SADB_RESERVED           0
 #define SADB_GETSPI             1
@@ -325,7 +335,8 @@ struct sadb_x_nat_t_port {
 #define SADB_X_EXT_NAT_T_SPORT          21
 #define SADB_X_EXT_NAT_T_DPORT          22
 #define SADB_X_EXT_NAT_T_OA             23
-#define SADB_EXT_MAX                    23
+#define SADB_X_EXT_SEC_CTX              24
+#define SADB_EXT_MAX                    24
 
 /* Identity Extension values */
 #define SADB_IDENTTYPE_RESERVED 0
diff --git a/include/linux/security.h b/include/linux/security.h
index f7e0ae018712..ef753654daa5 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -59,6 +59,12 @@ struct sk_buff;
 struct sock;
 struct sockaddr;
 struct socket;
+struct flowi;
+struct dst_entry;
+struct xfrm_selector;
+struct xfrm_policy;
+struct xfrm_state;
+struct xfrm_user_sec_ctx;
 
 extern int cap_netlink_send(struct sock *sk, struct sk_buff *skb);
 extern int cap_netlink_recv(struct sk_buff *skb);
@@ -788,6 +794,52 @@ struct swap_info_struct;
  *      which is used to copy security attributes between local stream sockets.
  * @sk_free_security:
  *      Deallocate security structure.
+ * @sk_getsid:
+ *      Retrieve the LSM-specific sid for the sock to enable caching of network
+ *      authorizations.
+ *
+ * Security hooks for XFRM operations.
+ *
+ * @xfrm_policy_alloc_security:
+ *      @xp contains the xfrm_policy being added to Security Policy Database
+ *      used by the XFRM system.
+ *      @sec_ctx contains the security context information being provided by
+ *      the user-level policy update program (e.g., setkey).
+ *      Allocate a security structure to the xp->selector.security field.
+ *      The security field is initialized to NULL when the xfrm_policy is
+ *      allocated.
+ *      Return 0 if operation was successful (memory to allocate, legal context)
+ * @xfrm_policy_clone_security:
+ *      @old contains an existing xfrm_policy in the SPD.
+ *      @new contains a new xfrm_policy being cloned from old.
+ *      Allocate a security structure to the new->selector.security field
+ *      that contains the information from the old->selector.security field.
+ *      Return 0 if operation was successful (memory to allocate).
+ * @xfrm_policy_free_security:
+ *      @xp contains the xfrm_policy
+ *      Deallocate xp->selector.security.
+ * @xfrm_state_alloc_security:
+ *      @x contains the xfrm_state being added to the Security Association
+ *      Database by the XFRM system.
+ *      @sec_ctx contains the security context information being provided by
+ *      the user-level SA generation program (e.g., setkey or racoon).
+ *      Allocate a security structure to the x->sel.security field.  The
+ *      security field is initialized to NULL when the xfrm_state is
+ *      allocated.
+ *      Return 0 if operation was successful (memory to allocate, legal context).
+ * @xfrm_state_free_security:
+ *      @x contains the xfrm_state.
+ *      Deallocate x>sel.security.
+ * @xfrm_policy_lookup:
+ *      @xp contains the xfrm_policy for which the access control is being
+ *      checked.
+ *      @sk_sid contains the sock security label that is used to authorize
+ *      access to the policy xp.
+ *      @dir contains the direction of the flow (input or output).
+ *      Check permission when a sock selects a xfrm_policy for processing
+ *      XFRMs on a packet.  The hook is called when selecting either a
+ *      per-socket policy or a generic xfrm policy.
+ *      Return 0 if permission is granted.
  *
  * Security hooks affecting all Key Management operations
  *
@@ -1237,8 +1289,18 @@ struct security_operations {
         int (*socket_getpeersec) (struct socket *sock, char __user *optval, int __user *optlen, unsigned len);
         int (*sk_alloc_security) (struct sock *sk, int family, gfp_t priority);
         void (*sk_free_security) (struct sock *sk);
+        unsigned int (*sk_getsid) (struct sock *sk, struct flowi *fl, u8 dir);
 #endif  /* CONFIG_SECURITY_NETWORK */
 
+#ifdef CONFIG_SECURITY_NETWORK_XFRM
+        int (*xfrm_policy_alloc_security) (struct xfrm_policy *xp, struct xfrm_user_sec_ctx *sec_ctx);
+        int (*xfrm_policy_clone_security) (struct xfrm_policy *old, struct xfrm_policy *new);
+        void (*xfrm_policy_free_security) (struct xfrm_policy *xp);
+        int (*xfrm_state_alloc_security) (struct xfrm_state *x, struct xfrm_user_sec_ctx *sec_ctx);
+        void (*xfrm_state_free_security) (struct xfrm_state *x);
+        int (*xfrm_policy_lookup)(struct xfrm_policy *xp, u32 sk_sid, u8 dir);
+#endif  /* CONFIG_SECURITY_NETWORK_XFRM */
+
         /* key management security hooks */
 #ifdef CONFIG_KEYS
         int (*key_alloc)(struct key *key);
@@ -2679,6 +2741,11 @@ static inline void security_sk_free(struct sock *sk)
 {
         return security_ops->sk_free_security(sk);
 }
+
+static inline unsigned int security_sk_sid(struct sock *sk, struct flowi *fl, u8 dir)
+{
+        return security_ops->sk_getsid(sk, fl, dir);
+}
 #else   /* CONFIG_SECURITY_NETWORK */
 static inline int security_unix_stream_connect(struct socket * sock,
                                                struct socket * other, 
@@ -2795,8 +2862,73 @@ static inline int security_sk_alloc(struct sock *sk, int family, gfp_t priority)
 static inline void security_sk_free(struct sock *sk)
 {
 }
+
+static inline unsigned int security_sk_sid(struct sock *sk, struct flowi *fl, u8 dir)
+{
+        return 0;
+}
 #endif  /* CONFIG_SECURITY_NETWORK */
 
+#ifdef CONFIG_SECURITY_NETWORK_XFRM
+static inline int security_xfrm_policy_alloc(struct xfrm_policy *xp, struct xfrm_user_sec_ctx *sec_ctx)
+{
+        return security_ops->xfrm_policy_alloc_security(xp, sec_ctx);
+}
+
+static inline int security_xfrm_policy_clone(struct xfrm_policy *old, struct xfrm_policy *new)
+{
+        return security_ops->xfrm_policy_clone_security(old, new);
+}
+
+static inline void security_xfrm_policy_free(struct xfrm_policy *xp)
+{
+        security_ops->xfrm_policy_free_security(xp);
+}
+
+static inline int security_xfrm_state_alloc(struct xfrm_state *x, struct xfrm_user_sec_ctx *sec_ctx)
+{
+        return security_ops->xfrm_state_alloc_security(x, sec_ctx);
+}
+
+static inline void security_xfrm_state_free(struct xfrm_state *x)
+{
+        security_ops->xfrm_state_free_security(x);
+}
+
+static inline int security_xfrm_policy_lookup(struct xfrm_policy *xp, u32 sk_sid, u8 dir)
+{
+        return security_ops->xfrm_policy_lookup(xp, sk_sid, dir);
+}
+#else   /* CONFIG_SECURITY_NETWORK_XFRM */
+static inline int security_xfrm_policy_alloc(struct xfrm_policy *xp, struct xfrm_user_sec_ctx *sec_ctx)
+{
+        return 0;
+}
+
+static inline int security_xfrm_policy_clone(struct xfrm_policy *old, struct xfrm_policy *new)
+{
+        return 0;
+}
+
+static inline void security_xfrm_policy_free(struct xfrm_policy *xp)
+{
+}
+
+static inline int security_xfrm_state_alloc(struct xfrm_state *x, struct xfrm_user_sec_ctx *sec_ctx)
+{
+        return 0;
+}
+
+static inline void security_xfrm_state_free(struct xfrm_state *x)
+{
+}
+
+static inline int security_xfrm_policy_lookup(struct xfrm_policy *xp, u32 sk_sid, u8 dir)
+{
+        return 0;
+}
+#endif  /* CONFIG_SECURITY_NETWORK_XFRM */
+
 #ifdef CONFIG_KEYS
 #ifdef CONFIG_SECURITY
 static inline int security_key_alloc(struct key *key)
diff --git a/include/linux/xfrm.h b/include/linux/xfrm.h
index 0fb077d68441..82fbb758e28f 100644
--- a/include/linux/xfrm.h
+++ b/include/linux/xfrm.h
@@ -27,6 +27,22 @@ struct xfrm_id
         __u8            proto;
 };
 
+struct xfrm_sec_ctx {
+        __u8    ctx_doi;
+        __u8    ctx_alg;
+        __u16   ctx_len;
+        __u32   ctx_sid;
+        char    ctx_str[0];
+};
+
+/* Security Context Domains of Interpretation */
+#define XFRM_SC_DOI_RESERVED 0
+#define XFRM_SC_DOI_LSM 1
+
+/* Security Context Algorithms */
+#define XFRM_SC_ALG_RESERVED 0
+#define XFRM_SC_ALG_SELINUX 1
+
 /* Selector, used as selector both on policy rules (SPD) and SAs. */
 
 struct xfrm_selector
@@ -146,6 +162,18 @@ enum {
 
 #define XFRM_NR_MSGTYPES (XFRM_MSG_MAX + 1 - XFRM_MSG_BASE)
 
+/*
+ * Generic LSM security context for comunicating to user space
+ * NOTE: Same format as sadb_x_sec_ctx
+ */
+struct xfrm_user_sec_ctx {
+        __u16                   len;
+        __u16                   exttype;
+        __u8                    ctx_alg;  /* LSMs: e.g., selinux == 1 */
+        __u8                    ctx_doi;
+        __u16                   ctx_len;
+};
+
 struct xfrm_user_tmpl {
         struct xfrm_id          id;
         __u16                   family;
@@ -176,6 +204,7 @@ enum xfrm_attr_type_t {
         XFRMA_TMPL,             /* 1 or more struct xfrm_user_tmpl */
         XFRMA_SA,
         XFRMA_POLICY,
+        XFRMA_SEC_CTX,          /* struct xfrm_sec_ctx */
         __XFRMA_MAX
 
 #define XFRMA_MAX (__XFRMA_MAX - 1)