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  *  Updated: Venkat Yekkirala <vyekkirala@TrustedCS.com>
  10  *
  11  *           Granular IPSec Associations for use in MLS environments.
  12  *
  13  *  Copyright (C) 2005 International Business Machines Corporation
  14  *  Copyright (C) 2006 Trusted Computer Solutions, Inc.
  15  *
  16  *      This program is free software; you can redistribute it and/or modify
  17  *      it under the terms of the GNU General Public License version 2,
  18  *      as published by the Free Software Foundation.
  19  */
  20
  21 /*
  22  * USAGE:
  23  * NOTES:
  24  *   1. Make sure to enable the following options in your kernel config:
  25  *      CONFIG_SECURITY=y
  26  *      CONFIG_SECURITY_NETWORK=y
  27  *      CONFIG_SECURITY_NETWORK_XFRM=y
  28  *      CONFIG_SECURITY_SELINUX=m/y
  29  * ISSUES:
  30  *   1. Caching packets, so they are not dropped during negotiation
  31  *   2. Emulating a reasonable SO_PEERSEC across machines
  32  *   3. Testing addition of sk_policy's with security context via setsockopt
  33  */
  34 #include <linux/kernel.h>
  35 #include <linux/init.h>
  36 #include <linux/security.h>
  37 #include <linux/types.h>
  38 #include <linux/netfilter.h>
  39 #include <linux/netfilter_ipv4.h>
  40 #include <linux/netfilter_ipv6.h>
  41 #include <linux/slab.h>
  42 #include <linux/ip.h>
  43 #include <linux/tcp.h>
  44 #include <linux/skbuff.h>
  45 #include <linux/xfrm.h>
  46 #include <net/xfrm.h>
  47 #include <net/checksum.h>
  48 #include <net/udp.h>
  49 #include <asm/atomic.h>
  50
  51 #include "avc.h"
  52 #include "objsec.h"
  53 #include "xfrm.h"
  54
  55 /* Labeled XFRM instance counter */
  56 atomic_t selinux_xfrm_refcount = ATOMIC_INIT(0);
  57
  58 /*
  59  * Returns true if an LSM/SELinux context
  60  */
  61 static inline int selinux_authorizable_ctx(struct xfrm_sec_ctx *ctx)
  62 {
  63         return (ctx &&
  64                 (ctx->ctx_doi == XFRM_SC_DOI_LSM) &&
  65                 (ctx->ctx_alg == XFRM_SC_ALG_SELINUX));
  66 }
  67
  68 /*
  69  * Returns true if the xfrm contains a security blob for SELinux
  70  */
  71 static inline int selinux_authorizable_xfrm(struct xfrm_state *x)
  72 {
  73         return selinux_authorizable_ctx(x->security);
  74 }
  75
  76 /*
  77  * LSM hook implementation that authorizes that a flow can use
  78  * a xfrm policy rule.
  79  */
  80 int selinux_xfrm_policy_lookup(struct xfrm_sec_ctx *ctx, u32 fl_secid, u8 dir)
  81 {
  82         int rc;
  83         u32 sel_sid;
  84
  85         /* Context sid is either set to label or ANY_ASSOC */
  86         if (ctx) {
  87                 if (!selinux_authorizable_ctx(ctx))
  88                         return -EINVAL;
  89
  90                 sel_sid = ctx->ctx_sid;
  91         } else
  92                 /*
  93                  * All flows should be treated as polmatch'ing an
  94                  * otherwise applicable "non-labeled" policy. This
  95                  * would prevent inadvertent "leaks".
  96                  */
  97                 return 0;
  98
  99         rc = avc_has_perm(fl_secid, sel_sid, SECCLASS_ASSOCIATION,
 100                           ASSOCIATION__POLMATCH,
 101                           NULL);
 102
 103         if (rc == -EACCES)
 104                 return -ESRCH;
 105
 106         return rc;
 107 }
 108
 109 /*
 110  * LSM hook implementation that authorizes that a state matches
 111  * the given policy, flow combo.
 112  */
 113
 114 int selinux_xfrm_state_pol_flow_match(struct xfrm_state *x, struct xfrm_policy *xp,
 115                         struct flowi *fl)
 116 {
 117         u32 state_sid;
 118         int rc;
 119
 120         if (!xp->security)
 121                 if (x->security)
 122                         /* unlabeled policy and labeled SA can't match */
 123                         return 0;
 124                 else
 125                         /* unlabeled policy and unlabeled SA match all flows */
 126                         return 1;
 127         else
 128                 if (!x->security)
 129                         /* unlabeled SA and labeled policy can't match */
 130                         return 0;
 131                 else
 132                         if (!selinux_authorizable_xfrm(x))
 133                                 /* Not a SELinux-labeled SA */
 134                                 return 0;
 135
 136         state_sid = x->security->ctx_sid;
 137
 138         if (fl->secid != state_sid)
 139                 return 0;
 140
 141         rc = avc_has_perm(fl->secid, state_sid, SECCLASS_ASSOCIATION,
 142                           ASSOCIATION__SENDTO,
 143                           NULL)? 0:1;
 144
 145         /*
 146          * We don't need a separate SA Vs. policy polmatch check
 147          * since the SA is now of the same label as the flow and
 148          * a flow Vs. policy polmatch check had already happened
 149          * in selinux_xfrm_policy_lookup() above.
 150          */
 151
 152         return rc;
 153 }
 154
 155 /*
 156  * LSM hook implementation that checks and/or returns the xfrm sid for the
 157  * incoming packet.
 158  */
 159
 160 int selinux_xfrm_decode_session(struct sk_buff *skb, u32 *sid, int ckall)
 161 {
 162         struct sec_path *sp;
 163
 164         *sid = SECSID_NULL;
 165
 166         if (skb == NULL)
 167                 return 0;
 168
 169         sp = skb->sp;
 170         if (sp) {
 171                 int i, sid_set = 0;
 172
 173                 for (i = sp->len-1; i >= 0; i--) {
 174                         struct xfrm_state *x = sp->xvec[i];
 175                         if (selinux_authorizable_xfrm(x)) {
 176                                 struct xfrm_sec_ctx *ctx = x->security;
 177
 178                                 if (!sid_set) {
 179                                         *sid = ctx->ctx_sid;
 180                                         sid_set = 1;
 181
 182                                         if (!ckall)
 183                                                 break;
 184                                 } else if (*sid != ctx->ctx_sid)
 185                                         return -EINVAL;
 186                         }
 187                 }
 188         }
 189
 190         return 0;
 191 }
 192
 193 /*
 194  * Security blob allocation for xfrm_policy and xfrm_state
 195  * CTX does not have a meaningful value on input
 196  */
 197 static int selinux_xfrm_sec_ctx_alloc(struct xfrm_sec_ctx **ctxp,
 198         struct xfrm_user_sec_ctx *uctx, u32 sid)
 199 {
 200         int rc = 0;
 201         const struct task_security_struct *tsec = current_security();
 202         struct xfrm_sec_ctx *ctx = NULL;
 203         char *ctx_str = NULL;
 204         u32 str_len;
 205
 206         BUG_ON(uctx && sid);
 207
 208         if (!uctx)
 209                 goto not_from_user;
 210
 211         if (uctx->ctx_doi != XFRM_SC_ALG_SELINUX)
 212                 return -EINVAL;
 213
 214         str_len = uctx->ctx_len;
 215         if (str_len >= PAGE_SIZE)
 216                 return -ENOMEM;
 217
 218         *ctxp = ctx = kmalloc(sizeof(*ctx) +
 219                               str_len + 1,
 220                               GFP_KERNEL);
 221
 222         if (!ctx)
 223                 return -ENOMEM;
 224
 225         ctx->ctx_doi = uctx->ctx_doi;
 226         ctx->ctx_len = str_len;
 227         ctx->ctx_alg = uctx->ctx_alg;
 228
 229         memcpy(ctx->ctx_str,
 230                uctx+1,
 231                str_len);
 232         ctx->ctx_str[str_len] = 0;
 233         rc = security_context_to_sid(ctx->ctx_str,
 234                                      str_len,
 235                                      &ctx->ctx_sid);
 236
 237         if (rc)
 238                 goto out;
 239
 240         /*
 241          * Does the subject have permission to set security context?
 242          */
 243         rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
 244                           SECCLASS_ASSOCIATION,
 245                           ASSOCIATION__SETCONTEXT, NULL);
 246         if (rc)
 247                 goto out;
 248
 249         return rc;
 250
 251 not_from_user:
 252         rc = security_sid_to_context(sid, &ctx_str, &str_len);
 253         if (rc)
 254                 goto out;
 255
 256         *ctxp = ctx = kmalloc(sizeof(*ctx) +
 257                               str_len,
 258                               GFP_ATOMIC);
 259
 260         if (!ctx) {
 261                 rc = -ENOMEM;
 262                 goto out;
 263         }
 264
 265         ctx->ctx_doi = XFRM_SC_DOI_LSM;
 266         ctx->ctx_alg = XFRM_SC_ALG_SELINUX;
 267         ctx->ctx_sid = sid;
 268         ctx->ctx_len = str_len;
 269         memcpy(ctx->ctx_str,
 270                ctx_str,
 271                str_len);
 272
 273         goto out2;
 274
 275 out:
 276         *ctxp = NULL;
 277         kfree(ctx);
 278 out2:
 279         kfree(ctx_str);
 280         return rc;
 281 }
 282
 283 /*
 284  * LSM hook implementation that allocs and transfers uctx spec to
 285  * xfrm_policy.
 286  */
 287 int selinux_xfrm_policy_alloc(struct xfrm_sec_ctx **ctxp,
 288                               struct xfrm_user_sec_ctx *uctx)
 289 {
 290         int err;
 291
 292         BUG_ON(!uctx);
 293
 294         err = selinux_xfrm_sec_ctx_alloc(ctxp, uctx, 0);
 295         if (err == 0)
 296                 atomic_inc(&selinux_xfrm_refcount);
 297
 298         return err;
 299 }
 300
 301
 302 /*
 303  * LSM hook implementation that copies security data structure from old to
 304  * new for policy cloning.
 305  */
 306 int selinux_xfrm_policy_clone(struct xfrm_sec_ctx *old_ctx,
 307                               struct xfrm_sec_ctx **new_ctxp)
 308 {
 309         struct xfrm_sec_ctx *new_ctx;
 310
 311         if (old_ctx) {
 312                 new_ctx = kmalloc(sizeof(*old_ctx) + old_ctx->ctx_len,
 313                                   GFP_KERNEL);
 314                 if (!new_ctx)
 315                         return -ENOMEM;
 316
 317                 memcpy(new_ctx, old_ctx, sizeof(*new_ctx));
 318                 memcpy(new_ctx->ctx_str, old_ctx->ctx_str, new_ctx->ctx_len);
 319                 *new_ctxp = new_ctx;
 320         }
 321         return 0;
 322 }
 323
 324 /*
 325  * LSM hook implementation that frees xfrm_sec_ctx security information.
 326  */
 327 void selinux_xfrm_policy_free(struct xfrm_sec_ctx *ctx)
 328 {
 329         kfree(ctx);
 330 }
 331
 332 /*
 333  * LSM hook implementation that authorizes deletion of labeled policies.
 334  */
 335 int selinux_xfrm_policy_delete(struct xfrm_sec_ctx *ctx)
 336 {
 337         const struct task_security_struct *tsec = current_security();
 338         int rc = 0;
 339
 340         if (ctx) {
 341                 rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
 342                                   SECCLASS_ASSOCIATION,
 343                                   ASSOCIATION__SETCONTEXT, NULL);
 344                 if (rc == 0)
 345                         atomic_dec(&selinux_xfrm_refcount);
 346         }
 347
 348         return rc;
 349 }
 350
 351 /*
 352  * LSM hook implementation that allocs and transfers sec_ctx spec to
 353  * xfrm_state.
 354  */
 355 int selinux_xfrm_state_alloc(struct xfrm_state *x, struct xfrm_user_sec_ctx *uctx,
 356                 u32 secid)
 357 {
 358         int err;
 359
 360         BUG_ON(!x);
 361
 362         err = selinux_xfrm_sec_ctx_alloc(&x->security, uctx, secid);
 363         if (err == 0)
 364                 atomic_inc(&selinux_xfrm_refcount);
 365         return err;
 366 }
 367
 368 /*
 369  * LSM hook implementation that frees xfrm_state security information.
 370  */
 371 void selinux_xfrm_state_free(struct xfrm_state *x)
 372 {
 373         struct xfrm_sec_ctx *ctx = x->security;
 374         kfree(ctx);
 375 }
 376
 377  /*
 378   * LSM hook implementation that authorizes deletion of labeled SAs.
 379   */
 380 int selinux_xfrm_state_delete(struct xfrm_state *x)
 381 {
 382         const struct task_security_struct *tsec = current_security();
 383         struct xfrm_sec_ctx *ctx = x->security;
 384         int rc = 0;
 385
 386         if (ctx) {
 387                 rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
 388                                   SECCLASS_ASSOCIATION,
 389                                   ASSOCIATION__SETCONTEXT, NULL);
 390                 if (rc == 0)
 391                         atomic_dec(&selinux_xfrm_refcount);
 392         }
 393
 394         return rc;
 395 }
 396
 397 /*
 398  * LSM hook that controls access to unlabelled packets.  If
 399  * a xfrm_state is authorizable (defined by macro) then it was
 400  * already authorized by the IPSec process.  If not, then
 401  * we need to check for unlabelled access since this may not have
 402  * gone thru the IPSec process.
 403  */
 404 int selinux_xfrm_sock_rcv_skb(u32 isec_sid, struct sk_buff *skb,
 405                                 struct common_audit_data *ad)
 406 {
 407         int i, rc = 0;
 408         struct sec_path *sp;
 409         u32 sel_sid = SECINITSID_UNLABELED;
 410
 411         sp = skb->sp;
 412
 413         if (sp) {
 414                 for (i = 0; i < sp->len; i++) {
 415                         struct xfrm_state *x = sp->xvec[i];
 416
 417                         if (x && selinux_authorizable_xfrm(x)) {
 418                                 struct xfrm_sec_ctx *ctx = x->security;
 419                                 sel_sid = ctx->ctx_sid;
 420                                 break;
 421                         }
 422                 }
 423         }
 424
 425         /*
 426          * This check even when there's no association involved is
 427          * intended, according to Trent Jaeger, to make sure a
 428          * process can't engage in non-ipsec communication unless
 429          * explicitly allowed by policy.
 430          */
 431
 432         rc = avc_has_perm(isec_sid, sel_sid, SECCLASS_ASSOCIATION,
 433                           ASSOCIATION__RECVFROM, ad);
 434
 435         return rc;
 436 }
 437
 438 /*
 439  * POSTROUTE_LAST hook's XFRM processing:
 440  * If we have no security association, then we need to determine
 441  * whether the socket is allowed to send to an unlabelled destination.
 442  * If we do have a authorizable security association, then it has already been
 443  * checked in the selinux_xfrm_state_pol_flow_match hook above.
 444  */
 445 int selinux_xfrm_postroute_last(u32 isec_sid, struct sk_buff *skb,
 446                                         struct common_audit_data *ad, u8 proto)
 447 {
 448         struct dst_entry *dst;
 449         int rc = 0;
 450
 451         dst = skb_dst(skb);
 452
 453         if (dst) {
 454                 struct dst_entry *dst_test;
 455
 456                 for (dst_test = dst; dst_test != NULL;
 457                      dst_test = dst_test->child) {
 458                         struct xfrm_state *x = dst_test->xfrm;
 459
 460                         if (x && selinux_authorizable_xfrm(x))
 461                                 goto out;
 462                 }
 463         }
 464
 465         switch (proto) {
 466         case IPPROTO_AH:
 467         case IPPROTO_ESP:
 468         case IPPROTO_COMP:
 469                 /*
 470                  * We should have already seen this packet once before
 471                  * it underwent xfrm(s). No need to subject it to the
 472                  * unlabeled check.
 473                  */
 474                 goto out;
 475         default:
 476                 break;
 477         }
 478
 479         /*
 480          * This check even when there's no association involved is
 481          * intended, according to Trent Jaeger, to make sure a
 482          * process can't engage in non-ipsec communication unless
 483          * explicitly allowed by policy.
 484          */
 485
 486         rc = avc_has_perm(isec_sid, SECINITSID_UNLABELED, SECCLASS_ASSOCIATION,
 487                           ASSOCIATION__SENDTO, ad);
 488 out:
 489         return rc;
 490 }