security/selinux/xfrm.c

   1 /*
   2  *  NSA Security-Enhanced Linux (SELinux) security module
   3  *
   4  *  This file contains the SELinux XFRM hook function implementations.
   5  *
   6  *  Authors:  Serge Hallyn <sergeh@us.ibm.com>
   7  *            Trent Jaeger <jaegert@us.ibm.com>
   8  *
   9  *  Copyright (C) 2005 International Business Machines Corporation
  10  *
  11  *      This program is free software; you can redistribute it and/or modify
  12  *      it under the terms of the GNU General Public License version 2,
  13  *      as published by the Free Software Foundation.
  14  */
  15
  16 /*
  17  * USAGE:
  18  * NOTES:
  19  *   1. Make sure to enable the following options in your kernel config:
  20  *      CONFIG_SECURITY=y
  21  *      CONFIG_SECURITY_NETWORK=y
  22  *      CONFIG_SECURITY_NETWORK_XFRM=y
  23  *      CONFIG_SECURITY_SELINUX=m/y
  24  * ISSUES:
  25  *   1. Caching packets, so they are not dropped during negotiation
  26  *   2. Emulating a reasonable SO_PEERSEC across machines
  27  *   3. Testing addition of sk_policy's with security context via setsockopt
  28  */
  29 #include <linux/config.h>
  30 #include <linux/module.h>
  31 #include <linux/kernel.h>
  32 #include <linux/init.h>
  33 #include <linux/security.h>
  34 #include <linux/types.h>
  35 #include <linux/netfilter.h>
  36 #include <linux/netfilter_ipv4.h>
  37 #include <linux/netfilter_ipv6.h>
  38 #include <linux/ip.h>
  39 #include <linux/tcp.h>
  40 #include <linux/skbuff.h>
  41 #include <linux/xfrm.h>
  42 #include <net/xfrm.h>
  43 #include <net/checksum.h>
  44 #include <net/udp.h>
  45 #include <asm/semaphore.h>
  46
  47 #include "avc.h"
  48 #include "objsec.h"
  49 #include "xfrm.h"
  50
  51
  52 /*
  53  * Returns true if an LSM/SELinux context
  54  */
  55 static inline int selinux_authorizable_ctx(struct xfrm_sec_ctx *ctx)
  56 {
  57         return (ctx &&
  58                 (ctx->ctx_doi == XFRM_SC_DOI_LSM) &&
  59                 (ctx->ctx_alg == XFRM_SC_ALG_SELINUX));
  60 }
  61
  62 /*
  63  * Returns true if the xfrm contains a security blob for SELinux
  64  */
  65 static inline int selinux_authorizable_xfrm(struct xfrm_state *x)
  66 {
  67         return selinux_authorizable_ctx(x->security);
  68 }
  69
  70 /*
  71  * LSM hook implementation that authorizes that a socket can be used
  72  * with the corresponding xfrm_sec_ctx and direction.
  73  */
  74 int selinux_xfrm_policy_lookup(struct xfrm_policy *xp, u32 sk_sid, u8 dir)
  75 {
  76         int rc = 0;
  77         u32 sel_sid = SECINITSID_UNLABELED;
  78         struct xfrm_sec_ctx *ctx;
  79
  80         /* Context sid is either set to label or ANY_ASSOC */
  81         if ((ctx = xp->security)) {
  82                 if (!selinux_authorizable_ctx(ctx))
  83                         return -EINVAL;
  84
  85                 sel_sid = ctx->ctx_sid;
  86         }
  87
  88         rc = avc_has_perm(sk_sid, sel_sid, SECCLASS_ASSOCIATION,
  89                           ((dir == FLOW_DIR_IN) ? ASSOCIATION__RECVFROM :
  90                            ((dir == FLOW_DIR_OUT) ?  ASSOCIATION__SENDTO :
  91                             (ASSOCIATION__SENDTO | ASSOCIATION__RECVFROM))),
  92                           NULL);
  93
  94         return rc;
  95 }
  96
  97 /*
  98  * Security blob allocation for xfrm_policy and xfrm_state
  99  * CTX does not have a meaningful value on input
 100  */
 101 static int selinux_xfrm_sec_ctx_alloc(struct xfrm_sec_ctx **ctxp, struct xfrm_user_sec_ctx *uctx)
 102 {
 103         int rc = 0;
 104         struct task_security_struct *tsec = current->security;
 105         struct xfrm_sec_ctx *ctx;
 106
 107         BUG_ON(!uctx);
 108         BUG_ON(uctx->ctx_doi != XFRM_SC_ALG_SELINUX);
 109
 110         if (uctx->ctx_len >= PAGE_SIZE)
 111                 return -ENOMEM;
 112
 113         *ctxp = ctx = kmalloc(sizeof(*ctx) +
 114                               uctx->ctx_len,
 115                               GFP_KERNEL);
 116
 117         if (!ctx)
 118                 return -ENOMEM;
 119
 120         ctx->ctx_doi = uctx->ctx_doi;
 121         ctx->ctx_len = uctx->ctx_len;
 122         ctx->ctx_alg = uctx->ctx_alg;
 123
 124         memcpy(ctx->ctx_str,
 125                uctx+1,
 126                ctx->ctx_len);
 127         rc = security_context_to_sid(ctx->ctx_str,
 128                                      ctx->ctx_len,
 129                                      &ctx->ctx_sid);
 130
 131         if (rc)
 132                 goto out;
 133
 134         /*
 135          * Does the subject have permission to set security context?
 136          */
 137         rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
 138                           SECCLASS_ASSOCIATION,
 139                           ASSOCIATION__SETCONTEXT, NULL);
 140         if (rc)
 141                 goto out;
 142
 143         return rc;
 144
 145 out:
 146         *ctxp = NULL;
 147         kfree(ctx);
 148         return rc;
 149 }
 150
 151 /*
 152  * LSM hook implementation that allocs and transfers uctx spec to
 153  * xfrm_policy.
 154  */
 155 int selinux_xfrm_policy_alloc(struct xfrm_policy *xp, struct xfrm_user_sec_ctx *uctx)
 156 {
 157         int err;
 158
 159         BUG_ON(!xp);
 160
 161         err = selinux_xfrm_sec_ctx_alloc(&xp->security, uctx);
 162         return err;
 163 }
 164
 165
 166 /*
 167  * LSM hook implementation that copies security data structure from old to
 168  * new for policy cloning.
 169  */
 170 int selinux_xfrm_policy_clone(struct xfrm_policy *old, struct xfrm_policy *new)
 171 {
 172         struct xfrm_sec_ctx *old_ctx, *new_ctx;
 173
 174         old_ctx = old->security;
 175
 176         if (old_ctx) {
 177                 new_ctx = new->security = kmalloc(sizeof(*new_ctx) +
 178                                                   old_ctx->ctx_len,
 179                                                   GFP_KERNEL);
 180
 181                 if (!new_ctx)
 182                         return -ENOMEM;
 183
 184                 memcpy(new_ctx, old_ctx, sizeof(*new_ctx));
 185                 memcpy(new_ctx->ctx_str, old_ctx->ctx_str, new_ctx->ctx_len);
 186         }
 187         return 0;
 188 }
 189
 190 /*
 191  * LSM hook implementation that frees xfrm_policy security information.
 192  */
 193 void selinux_xfrm_policy_free(struct xfrm_policy *xp)
 194 {
 195         struct xfrm_sec_ctx *ctx = xp->security;
 196         if (ctx)
 197                 kfree(ctx);
 198 }
 199
 200 /*
 201  * LSM hook implementation that authorizes deletion of labeled policies.
 202  */
 203 int selinux_xfrm_policy_delete(struct xfrm_policy *xp)
 204 {
 205         struct task_security_struct *tsec = current->security;
 206         struct xfrm_sec_ctx *ctx = xp->security;
 207         int rc = 0;
 208
 209         if (ctx)
 210                 rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
 211                                   SECCLASS_ASSOCIATION,
 212                                   ASSOCIATION__SETCONTEXT, NULL);
 213
 214         return rc;
 215 }
 216
 217 /*
 218  * LSM hook implementation that allocs and transfers sec_ctx spec to
 219  * xfrm_state.
 220  */
 221 int selinux_xfrm_state_alloc(struct xfrm_state *x, struct xfrm_user_sec_ctx *uctx)
 222 {
 223         int err;
 224
 225         BUG_ON(!x);
 226
 227         err = selinux_xfrm_sec_ctx_alloc(&x->security, uctx);
 228         return err;
 229 }
 230
 231 /*
 232  * LSM hook implementation that frees xfrm_state security information.
 233  */
 234 void selinux_xfrm_state_free(struct xfrm_state *x)
 235 {
 236         struct xfrm_sec_ctx *ctx = x->security;
 237         if (ctx)
 238                 kfree(ctx);
 239 }
 240
 241 /*
 242  * SELinux internal function to retrieve the context of a connected
 243  * (sk->sk_state == TCP_ESTABLISHED) TCP socket based on its security
 244  * association used to connect to the remote socket.
 245  *
 246  * Retrieve via getsockopt SO_PEERSEC.
 247  */
 248 u32 selinux_socket_getpeer_stream(struct sock *sk)
 249 {
 250         struct dst_entry *dst, *dst_test;
 251         u32 peer_sid = SECSID_NULL;
 252
 253         if (sk->sk_state != TCP_ESTABLISHED)
 254                 goto out;
 255
 256         dst = sk_dst_get(sk);
 257         if (!dst)
 258                 goto out;
 259
 260         for (dst_test = dst; dst_test != 0;
 261              dst_test = dst_test->child) {
 262                 struct xfrm_state *x = dst_test->xfrm;
 263
 264                 if (x && selinux_authorizable_xfrm(x)) {
 265                         struct xfrm_sec_ctx *ctx = x->security;
 266                         peer_sid = ctx->ctx_sid;
 267                         break;
 268                 }
 269         }
 270         dst_release(dst);
 271
 272 out:
 273         return peer_sid;
 274 }
 275
 276 /*
 277  * SELinux internal function to retrieve the context of a UDP packet
 278  * based on its security association used to connect to the remote socket.
 279  *
 280  * Retrieve via setsockopt IP_PASSSEC and recvmsg with control message
 281  * type SCM_SECURITY.
 282  */
 283 u32 selinux_socket_getpeer_dgram(struct sk_buff *skb)
 284 {
 285         struct sec_path *sp;
 286
 287         if (skb == NULL)
 288                 return SECSID_NULL;
 289
 290         if (skb->sk->sk_protocol != IPPROTO_UDP)
 291                 return SECSID_NULL;
 292
 293         sp = skb->sp;
 294         if (sp) {
 295                 int i;
 296
 297                 for (i = sp->len-1; i >= 0; i--) {
 298                         struct xfrm_state *x = sp->xvec[i];
 299                         if (selinux_authorizable_xfrm(x)) {
 300                                 struct xfrm_sec_ctx *ctx = x->security;
 301                                 return ctx->ctx_sid;
 302                         }
 303                 }
 304         }
 305
 306         return SECSID_NULL;
 307 }
 308
 309  /*
 310   * LSM hook implementation that authorizes deletion of labeled SAs.
 311   */
 312 int selinux_xfrm_state_delete(struct xfrm_state *x)
 313 {
 314         struct task_security_struct *tsec = current->security;
 315         struct xfrm_sec_ctx *ctx = x->security;
 316         int rc = 0;
 317
 318         if (ctx)
 319                 rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
 320                                   SECCLASS_ASSOCIATION,
 321                                   ASSOCIATION__SETCONTEXT, NULL);
 322
 323         return rc;
 324 }
 325
 326 /*
 327  * LSM hook that controls access to unlabelled packets.  If
 328  * a xfrm_state is authorizable (defined by macro) then it was
 329  * already authorized by the IPSec process.  If not, then
 330  * we need to check for unlabelled access since this may not have
 331  * gone thru the IPSec process.
 332  */
 333 int selinux_xfrm_sock_rcv_skb(u32 isec_sid, struct sk_buff *skb)
 334 {
 335         int i, rc = 0;
 336         struct sec_path *sp;
 337
 338         sp = skb->sp;
 339
 340         if (sp) {
 341                 /*
 342                  * __xfrm_policy_check does not approve unless xfrm_policy_ok
 343                  * says that spi's match for policy and the socket.
 344                  *
 345                  *  Only need to verify the existence of an authorizable sp.
 346                  */
 347                 for (i = 0; i < sp->len; i++) {
 348                         struct xfrm_state *x = sp->xvec[i];
 349
 350                         if (x && selinux_authorizable_xfrm(x))
 351                                 goto accept;
 352                 }
 353         }
 354
 355         /* check SELinux sock for unlabelled access */
 356         rc = avc_has_perm(isec_sid, SECINITSID_UNLABELED, SECCLASS_ASSOCIATION,
 357                           ASSOCIATION__RECVFROM, NULL);
 358         if (rc)
 359                 goto drop;
 360
 361 accept:
 362         return 0;
 363
 364 drop:
 365         return rc;
 366 }
 367
 368 /*
 369  * POSTROUTE_LAST hook's XFRM processing:
 370  * If we have no security association, then we need to determine
 371  * whether the socket is allowed to send to an unlabelled destination.
 372  * If we do have a authorizable security association, then it has already been
 373  * checked in xfrm_policy_lookup hook.
 374  */
 375 int selinux_xfrm_postroute_last(u32 isec_sid, struct sk_buff *skb)
 376 {
 377         struct dst_entry *dst;
 378         int rc = 0;
 379
 380         dst = skb->dst;
 381
 382         if (dst) {
 383                 struct dst_entry *dst_test;
 384
 385                 for (dst_test = dst; dst_test != 0;
 386                      dst_test = dst_test->child) {
 387                         struct xfrm_state *x = dst_test->xfrm;
 388
 389                         if (x && selinux_authorizable_xfrm(x))
 390                                 goto out;
 391                 }
 392         }
 393
 394         rc = avc_has_perm(isec_sid, SECINITSID_UNLABELED, SECCLASS_ASSOCIATION,
 395                           ASSOCIATION__SENDTO, NULL);
 396 out:
 397         return rc;
 398 }