[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, 189 insertions, 8 deletions

diff --git a/net/key/af_key.c b/net/key/af_key.c
index 39031684b65c..d32f7791f1e4 100644
--- a/net/key/af_key.c
+++ b/net/key/af_key.c
@@ -336,6 +336,7 @@ static u8 sadb_ext_min_len[] = {
         [SADB_X_EXT_NAT_T_SPORT]        = (u8) sizeof(struct sadb_x_nat_t_port),
         [SADB_X_EXT_NAT_T_DPORT]        = (u8) sizeof(struct sadb_x_nat_t_port),
         [SADB_X_EXT_NAT_T_OA]           = (u8) sizeof(struct sadb_address),
+        [SADB_X_EXT_SEC_CTX]            = (u8) sizeof(struct sadb_x_sec_ctx),
 };
 
 /* Verify sadb_address_{len,prefixlen} against sa_family.  */
@@ -383,6 +384,55 @@ static int verify_address_len(void *p)
         return 0;
 }
 
+static inline int pfkey_sec_ctx_len(struct sadb_x_sec_ctx *sec_ctx)
+{
+        int len = 0;
+
+        len += sizeof(struct sadb_x_sec_ctx);
+        len += sec_ctx->sadb_x_ctx_len;
+        len += sizeof(uint64_t) - 1;
+        len /= sizeof(uint64_t);
+
+        return len;
+}
+
+static inline int verify_sec_ctx_len(void *p)
+{
+        struct sadb_x_sec_ctx *sec_ctx = (struct sadb_x_sec_ctx *)p;
+        int len;
+
+        if (sec_ctx->sadb_x_ctx_len > PAGE_SIZE)
+                return -EINVAL;
+
+        len = pfkey_sec_ctx_len(sec_ctx);
+
+        if (sec_ctx->sadb_x_sec_len != len)
+                return -EINVAL;
+
+        return 0;
+}
+
+static inline struct xfrm_user_sec_ctx *pfkey_sadb2xfrm_user_sec_ctx(struct sadb_x_sec_ctx *sec_ctx)
+{
+        struct xfrm_user_sec_ctx *uctx = NULL;
+        int ctx_size = sec_ctx->sadb_x_ctx_len;
+
+        uctx = kmalloc((sizeof(*uctx)+ctx_size), GFP_KERNEL);
+
+        if (!uctx)
+                return NULL;
+
+        uctx->len = pfkey_sec_ctx_len(sec_ctx);
+        uctx->exttype = sec_ctx->sadb_x_sec_exttype;
+        uctx->ctx_doi = sec_ctx->sadb_x_ctx_doi;
+        uctx->ctx_alg = sec_ctx->sadb_x_ctx_alg;
+        uctx->ctx_len = sec_ctx->sadb_x_ctx_len;
+        memcpy(uctx + 1, sec_ctx + 1,
+               uctx->ctx_len);
+
+        return uctx;
+}
+
 static int present_and_same_family(struct sadb_address *src,
                                    struct sadb_address *dst)
 {
@@ -438,6 +488,10 @@ static int parse_exthdrs(struct sk_buff *skb, struct sadb_msg *hdr, void **ext_h
                                 if (verify_address_len(p))
                                         return -EINVAL;
                         }                               
+                        if (ext_type == SADB_X_EXT_SEC_CTX) {
+                                if (verify_sec_ctx_len(p))
+                                        return -EINVAL;
+                        }
                         ext_hdrs[ext_type-1] = p;
                 }
                 p   += ext_len;
@@ -586,6 +640,9 @@ static struct sk_buff * pfkey_xfrm_state2msg(struct xfrm_state *x, int add_keys,
         struct sadb_key *key;
         struct sadb_x_sa2 *sa2;
         struct sockaddr_in *sin;
+        struct sadb_x_sec_ctx *sec_ctx;
+        struct xfrm_sec_ctx *xfrm_ctx;
+        int ctx_size = 0;
 #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
         struct sockaddr_in6 *sin6;
 #endif
@@ -609,6 +666,12 @@ static struct sk_buff * pfkey_xfrm_state2msg(struct xfrm_state *x, int add_keys,
                         sizeof(struct sadb_address)*2 + 
                                 sockaddr_size*2 +
                                         sizeof(struct sadb_x_sa2);
+
+        if ((xfrm_ctx = x->security)) {
+                ctx_size = PFKEY_ALIGN8(xfrm_ctx->ctx_len);
+                size += sizeof(struct sadb_x_sec_ctx) + ctx_size;
+        }
+
         /* identity & sensitivity */
 
         if ((x->props.family == AF_INET &&
@@ -899,6 +962,20 @@ static struct sk_buff * pfkey_xfrm_state2msg(struct xfrm_state *x, int add_keys,
                 n_port->sadb_x_nat_t_port_reserved = 0;
         }
 
+        /* security context */
+        if (xfrm_ctx) {
+                sec_ctx = (struct sadb_x_sec_ctx *) skb_put(skb,
+                                sizeof(struct sadb_x_sec_ctx) + ctx_size);
+                sec_ctx->sadb_x_sec_len =
+                  (sizeof(struct sadb_x_sec_ctx) + ctx_size) / sizeof(uint64_t);
+                sec_ctx->sadb_x_sec_exttype = SADB_X_EXT_SEC_CTX;
+                sec_ctx->sadb_x_ctx_doi = xfrm_ctx->ctx_doi;
+                sec_ctx->sadb_x_ctx_alg = xfrm_ctx->ctx_alg;
+                sec_ctx->sadb_x_ctx_len = xfrm_ctx->ctx_len;
+                memcpy(sec_ctx + 1, xfrm_ctx->ctx_str,
+                       xfrm_ctx->ctx_len);
+        }
+
         return skb;
 }
 
@@ -909,6 +986,7 @@ static struct xfrm_state * pfkey_msg2xfrm_state(struct sadb_msg *hdr,
         struct sadb_lifetime *lifetime;
         struct sadb_sa *sa;
         struct sadb_key *key;
+        struct sadb_x_sec_ctx *sec_ctx;
         uint16_t proto;
         int err;
         
@@ -993,6 +1071,21 @@ static struct xfrm_state * pfkey_msg2xfrm_state(struct sadb_msg *hdr,
                 x->lft.soft_add_expires_seconds = lifetime->sadb_lifetime_addtime;
                 x->lft.soft_use_expires_seconds = lifetime->sadb_lifetime_usetime;
         }
+
+        sec_ctx = (struct sadb_x_sec_ctx *) ext_hdrs[SADB_X_EXT_SEC_CTX-1];
+        if (sec_ctx != NULL) {
+                struct xfrm_user_sec_ctx *uctx = pfkey_sadb2xfrm_user_sec_ctx(sec_ctx);
+
+                if (!uctx)
+                        goto out;
+
+                err = security_xfrm_state_alloc(x, uctx);
+                kfree(uctx);
+
+                if (err)
+                        goto out;
+        }
+
         key = (struct sadb_key*) ext_hdrs[SADB_EXT_KEY_AUTH-1];
         if (sa->sadb_sa_auth) {
                 int keysize = 0;
@@ -1720,6 +1813,18 @@ parse_ipsecrequests(struct xfrm_policy *xp, struct sadb_x_policy *pol)
         return 0;
 }
 
+static inline int pfkey_xfrm_policy2sec_ctx_size(struct xfrm_policy *xp)
+{
+  struct xfrm_sec_ctx *xfrm_ctx = xp->security;
+
+        if (xfrm_ctx) {
+                int len = sizeof(struct sadb_x_sec_ctx);
+                len += xfrm_ctx->ctx_len;
+                return PFKEY_ALIGN8(len);
+        }
+        return 0;
+}
+
 static int pfkey_xfrm_policy2msg_size(struct xfrm_policy *xp)
 {
         int sockaddr_size = pfkey_sockaddr_size(xp->family);
@@ -1733,7 +1838,8 @@ static int pfkey_xfrm_policy2msg_size(struct xfrm_policy *xp)
                 (sockaddr_size * 2) +
                 sizeof(struct sadb_x_policy) +
                 (xp->xfrm_nr * (sizeof(struct sadb_x_ipsecrequest) +
-                                (socklen * 2)));
+                                (socklen * 2))) +
+                pfkey_xfrm_policy2sec_ctx_size(xp);
 }
 
 static struct sk_buff * pfkey_xfrm_policy2msg_prep(struct xfrm_policy *xp)
@@ -1757,6 +1863,8 @@ static void pfkey_xfrm_policy2msg(struct sk_buff *skb, struct xfrm_policy *xp, i
         struct sadb_lifetime *lifetime;
         struct sadb_x_policy *pol;
         struct sockaddr_in   *sin;
+        struct sadb_x_sec_ctx *sec_ctx;
+        struct xfrm_sec_ctx *xfrm_ctx;
 #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
         struct sockaddr_in6  *sin6;
 #endif
@@ -1941,6 +2049,21 @@ static void pfkey_xfrm_policy2msg(struct sk_buff *skb, struct xfrm_policy *xp, i
                         }
                 }
         }
+
+        /* security context */
+        if ((xfrm_ctx = xp->security)) {
+                int ctx_size = pfkey_xfrm_policy2sec_ctx_size(xp);
+
+                sec_ctx = (struct sadb_x_sec_ctx *) skb_put(skb, ctx_size);
+                sec_ctx->sadb_x_sec_len = ctx_size / sizeof(uint64_t);
+                sec_ctx->sadb_x_sec_exttype = SADB_X_EXT_SEC_CTX;
+                sec_ctx->sadb_x_ctx_doi = xfrm_ctx->ctx_doi;
+                sec_ctx->sadb_x_ctx_alg = xfrm_ctx->ctx_alg;
+                sec_ctx->sadb_x_ctx_len = xfrm_ctx->ctx_len;
+                memcpy(sec_ctx + 1, xfrm_ctx->ctx_str,
+                       xfrm_ctx->ctx_len);
+        }
+
         hdr->sadb_msg_len = size / sizeof(uint64_t);
         hdr->sadb_msg_reserved = atomic_read(&xp->refcnt);
 }
@@ -1976,12 +2099,13 @@ out:
 
 static int pfkey_spdadd(struct sock *sk, struct sk_buff *skb, struct sadb_msg *hdr, void **ext_hdrs)
 {
-        int err;
+        int err = 0;
         struct sadb_lifetime *lifetime;
         struct sadb_address *sa;
         struct sadb_x_policy *pol;
         struct xfrm_policy *xp;
         struct km_event c;
+        struct sadb_x_sec_ctx *sec_ctx;
 
         if (!present_and_same_family(ext_hdrs[SADB_EXT_ADDRESS_SRC-1],
                                      ext_hdrs[SADB_EXT_ADDRESS_DST-1]) ||
@@ -2028,6 +2152,22 @@ static int pfkey_spdadd(struct sock *sk, struct sk_buff *skb, struct sadb_msg *h
         if (xp->selector.dport)
                 xp->selector.dport_mask = ~0;
 
+        sec_ctx = (struct sadb_x_sec_ctx *) ext_hdrs[SADB_X_EXT_SEC_CTX-1];
+        if (sec_ctx != NULL) {
+                struct xfrm_user_sec_ctx *uctx = pfkey_sadb2xfrm_user_sec_ctx(sec_ctx);
+
+                if (!uctx) {
+                        err = -ENOBUFS;
+                        goto out;
+                }
+
+                err = security_xfrm_policy_alloc(xp, uctx);
+                kfree(uctx);
+
+                if (err)
+                        goto out;
+        }
+
         xp->lft.soft_byte_limit = XFRM_INF;
         xp->lft.hard_byte_limit = XFRM_INF;
         xp->lft.soft_packet_limit = XFRM_INF;
@@ -2051,10 +2191,9 @@ static int pfkey_spdadd(struct sock *sk, struct sk_buff *skb, struct sadb_msg *h
 
         err = xfrm_policy_insert(pol->sadb_x_policy_dir-1, xp,
                                  hdr->sadb_msg_type != SADB_X_SPDUPDATE);
-        if (err) {
-                kfree(xp);
-                return err;
-        }
+
+        if (err)
+                goto out;
 
         if (hdr->sadb_msg_type == SADB_X_SPDUPDATE)
                 c.event = XFRM_MSG_UPDPOLICY;
@@ -2069,6 +2208,7 @@ static int pfkey_spdadd(struct sock *sk, struct sk_buff *skb, struct sadb_msg *h
         return 0;
 
 out:
+        security_xfrm_policy_free(xp);
         kfree(xp);
         return err;
 }
@@ -2078,9 +2218,10 @@ static int pfkey_spddelete(struct sock *sk, struct sk_buff *skb, struct sadb_msg
         int err;
         struct sadb_address *sa;
         struct sadb_x_policy *pol;
-        struct xfrm_policy *xp;
+        struct xfrm_policy *xp, tmp;
         struct xfrm_selector sel;
         struct km_event c;
+        struct sadb_x_sec_ctx *sec_ctx;
 
         if (!present_and_same_family(ext_hdrs[SADB_EXT_ADDRESS_SRC-1],
                                      ext_hdrs[SADB_EXT_ADDRESS_DST-1]) ||
@@ -2109,7 +2250,24 @@ static int pfkey_spddelete(struct sock *sk, struct sk_buff *skb, struct sadb_msg
         if (sel.dport)
                 sel.dport_mask = ~0;
 
-        xp = xfrm_policy_bysel(pol->sadb_x_policy_dir-1, &sel, 1);
+        sec_ctx = (struct sadb_x_sec_ctx *) ext_hdrs[SADB_X_EXT_SEC_CTX-1];
+        memset(&tmp, 0, sizeof(struct xfrm_policy));
+
+        if (sec_ctx != NULL) {
+                struct xfrm_user_sec_ctx *uctx = pfkey_sadb2xfrm_user_sec_ctx(sec_ctx);
+
+                if (!uctx)
+                        return -ENOMEM;
+
+                err = security_xfrm_policy_alloc(&tmp, uctx);
+                kfree(uctx);
+
+                if (err)
+                        return err;
+        }
+
+        xp = xfrm_policy_bysel_ctx(pol->sadb_x_policy_dir-1, &sel, tmp.security, 1);
+        security_xfrm_policy_free(&tmp);
         if (xp == NULL)
                 return -ENOENT;
 
@@ -2660,6 +2818,7 @@ static struct xfrm_policy *pfkey_compile_policy(u16 family, int opt,
 {
         struct xfrm_policy *xp;
         struct sadb_x_policy *pol = (struct sadb_x_policy*)data;
+        struct sadb_x_sec_ctx *sec_ctx;
 
         switch (family) {
         case AF_INET:
@@ -2709,10 +2868,32 @@ static struct xfrm_policy *pfkey_compile_policy(u16 family, int opt,
             (*dir = parse_ipsecrequests(xp, pol)) < 0)
                 goto out;
 
+        /* security context too */
+        if (len >= (pol->sadb_x_policy_len*8 +
+            sizeof(struct sadb_x_sec_ctx))) {
+                char *p = (char *)pol;
+                struct xfrm_user_sec_ctx *uctx;
+
+                p += pol->sadb_x_policy_len*8;
+                sec_ctx = (struct sadb_x_sec_ctx *)p;
+                if (len < pol->sadb_x_policy_len*8 +
+                    sec_ctx->sadb_x_sec_len)
+                        goto out;
+                if ((*dir = verify_sec_ctx_len(p)))
+                        goto out;
+                uctx = pfkey_sadb2xfrm_user_sec_ctx(sec_ctx);
+                *dir = security_xfrm_policy_alloc(xp, uctx);
+                kfree(uctx);
+
+                if (*dir)
+                        goto out;
+        }
+
         *dir = pol->sadb_x_policy_dir-1;
         return xp;
 
 out:
+        security_xfrm_policy_free(xp);
         kfree(xp);
         return NULL;
 }