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/ip.h>
  42 #include <linux/tcp.h>
  43 #include <linux/skbuff.h>
  44 #include <linux/xfrm.h>
  45 #include <net/xfrm.h>
  46 #include <net/checksum.h>
  47 #include <net/udp.h>
  48 #include <asm/semaphore.h>
  49
  50 #include "avc.h"
  51 #include "objsec.h"
  52 #include "xfrm.h"
  53
  54
  55 /*
  56  * Returns true if an LSM/SELinux context
  57  */
  58 static inline int selinux_authorizable_ctx(struct xfrm_sec_ctx *ctx)
  59 {
  60         return (ctx &&
  61                 (ctx->ctx_doi == XFRM_SC_DOI_LSM) &&
  62                 (ctx->ctx_alg == XFRM_SC_ALG_SELINUX));
  63 }
  64
  65 /*
  66  * Returns true if the xfrm contains a security blob for SELinux
  67  */
  68 static inline int selinux_authorizable_xfrm(struct xfrm_state *x)
  69 {
  70         return selinux_authorizable_ctx(x->security);
  71 }
  72
  73 /*
  74  * LSM hook implementation that authorizes that a flow can use
  75  * a xfrm policy rule.
  76  */
  77 int selinux_xfrm_policy_lookup(struct xfrm_policy *xp, u32 fl_secid, u8 dir)
  78 {
  79         int rc;
  80         u32 sel_sid;
  81         struct xfrm_sec_ctx *ctx;
  82
  83         /* Context sid is either set to label or ANY_ASSOC */
  84         if ((ctx = xp->security)) {
  85                 if (!selinux_authorizable_ctx(ctx))
  86                         return -EINVAL;
  87
  88                 sel_sid = ctx->ctx_sid;
  89         }
  90         else
  91                 /*
  92                  * All flows should be treated as polmatch'ing an
  93                  * otherwise applicable "non-labeled" policy. This
  94                  * would prevent inadvertent "leaks".
  95                  */
  96                 return 0;
  97
  98         rc = avc_has_perm(fl_secid, sel_sid, SECCLASS_ASSOCIATION,
  99                           ASSOCIATION__POLMATCH,
 100                           NULL);
 101
 102         if (rc == -EACCES)
 103                 rc = -ESRCH;
 104
 105         return rc;
 106 }
 107
 108 /*
 109  * LSM hook implementation that authorizes that a state matches
 110  * the given policy, flow combo.
 111  */
 112
 113 int selinux_xfrm_state_pol_flow_match(struct xfrm_state *x, struct xfrm_policy *xp,
 114                         struct flowi *fl)
 115 {
 116         u32 state_sid;
 117         int rc;
 118
 119         if (!xp->security)
 120                 if (x->security)
 121                         /* unlabeled policy and labeled SA can't match */
 122                         return 0;
 123                 else
 124                         /* unlabeled policy and unlabeled SA match all flows */
 125                         return 1;
 126         else
 127                 if (!x->security)
 128                         /* unlabeled SA and labeled policy can't match */
 129                         return 0;
 130                 else
 131                         if (!selinux_authorizable_xfrm(x))
 132                                 /* Not a SELinux-labeled SA */
 133                                 return 0;
 134
 135         state_sid = x->security->ctx_sid;
 136
 137         if (fl->secid != state_sid)
 138                 return 0;
 139
 140         rc = avc_has_perm(fl->secid, state_sid, SECCLASS_ASSOCIATION,
 141                           ASSOCIATION__SENDTO,
 142                           NULL)? 0:1;
 143
 144         /*
 145          * We don't need a separate SA Vs. policy polmatch check
 146          * since the SA is now of the same label as the flow and
 147          * a flow Vs. policy polmatch check had already happened
 148          * in selinux_xfrm_policy_lookup() above.
 149          */
 150
 151         return rc;
 152 }
 153
 154 /*
 155  * LSM hook implementation that checks and/or returns the xfrm sid for the
 156  * incoming packet.
 157  */
 158
 159 int selinux_xfrm_decode_session(struct sk_buff *skb, u32 *sid, int ckall)
 160 {
 161         struct sec_path *sp;
 162
 163         *sid = SECSID_NULL;
 164
 165         if (skb == NULL)
 166                 return 0;
 167
 168         sp = skb->sp;
 169         if (sp) {
 170                 int i, sid_set = 0;
 171
 172                 for (i = sp->len-1; i >= 0; i--) {
 173                         struct xfrm_state *x = sp->xvec[i];
 174                         if (selinux_authorizable_xfrm(x)) {
 175                                 struct xfrm_sec_ctx *ctx = x->security;
 176
 177                                 if (!sid_set) {
 178                                         *sid = ctx->ctx_sid;
 179                                         sid_set = 1;
 180
 181                                         if (!ckall)
 182                                                 break;
 183                                 }
 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         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         if (uctx->ctx_len >= PAGE_SIZE)
 215                 return -ENOMEM;
 216
 217         *ctxp = ctx = kmalloc(sizeof(*ctx) +
 218                               uctx->ctx_len + 1,
 219                               GFP_KERNEL);
 220
 221         if (!ctx)
 222                 return -ENOMEM;
 223
 224         ctx->ctx_doi = uctx->ctx_doi;
 225         ctx->ctx_len = uctx->ctx_len;
 226         ctx->ctx_alg = uctx->ctx_alg;
 227
 228         memcpy(ctx->ctx_str,
 229                uctx+1,
 230                ctx->ctx_len);
 231         ctx->ctx_str[ctx->ctx_len] = 0;
 232         rc = security_context_to_sid(ctx->ctx_str,
 233                                      ctx->ctx_len,
 234                                      &ctx->ctx_sid);
 235
 236         if (rc)
 237                 goto out;
 238
 239         /*
 240          * Does the subject have permission to set security context?
 241          */
 242         rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
 243                           SECCLASS_ASSOCIATION,
 244                           ASSOCIATION__SETCONTEXT, NULL);
 245         if (rc)
 246                 goto out;
 247
 248         return rc;
 249
 250 not_from_user:
 251         rc = security_sid_to_context(sid, &ctx_str, &str_len);
 252         if (rc)
 253                 goto out;
 254
 255         *ctxp = ctx = kmalloc(sizeof(*ctx) +
 256                               str_len,
 257                               GFP_ATOMIC);
 258
 259         if (!ctx) {
 260                 rc = -ENOMEM;
 261                 goto out;
 262         }
 263
 264         ctx->ctx_doi = XFRM_SC_DOI_LSM;
 265         ctx->ctx_alg = XFRM_SC_ALG_SELINUX;
 266         ctx->ctx_sid = sid;
 267         ctx->ctx_len = str_len;
 268         memcpy(ctx->ctx_str,
 269                ctx_str,
 270                str_len);
 271
 272         goto out2;
 273
 274 out:
 275         *ctxp = NULL;
 276         kfree(ctx);
 277 out2:
 278         kfree(ctx_str);
 279         return rc;
 280 }
 281
 282 /*
 283  * LSM hook implementation that allocs and transfers uctx spec to
 284  * xfrm_policy.
 285  */
 286 int selinux_xfrm_policy_alloc(struct xfrm_policy *xp,
 287                 struct xfrm_user_sec_ctx *uctx)
 288 {
 289         int err;
 290
 291         BUG_ON(!xp);
 292         BUG_ON(!uctx);
 293
 294         err = selinux_xfrm_sec_ctx_alloc(&xp->security, uctx, 0);
 295         return err;
 296 }
 297
 298
 299 /*
 300  * LSM hook implementation that copies security data structure from old to
 301  * new for policy cloning.
 302  */
 303 int selinux_xfrm_policy_clone(struct xfrm_policy *old, struct xfrm_policy *new)
 304 {
 305         struct xfrm_sec_ctx *old_ctx, *new_ctx;
 306
 307         old_ctx = old->security;
 308
 309         if (old_ctx) {
 310                 new_ctx = new->security = kmalloc(sizeof(*new_ctx) +
 311                                                   old_ctx->ctx_len,
 312                                                   GFP_KERNEL);
 313
 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         }
 320         return 0;
 321 }
 322
 323 /*
 324  * LSM hook implementation that frees xfrm_policy security information.
 325  */
 326 void selinux_xfrm_policy_free(struct xfrm_policy *xp)
 327 {
 328         struct xfrm_sec_ctx *ctx = xp->security;
 329         if (ctx)
 330                 kfree(ctx);
 331 }
 332
 333 /*
 334  * LSM hook implementation that authorizes deletion of labeled policies.
 335  */
 336 int selinux_xfrm_policy_delete(struct xfrm_policy *xp)
 337 {
 338         struct task_security_struct *tsec = current->security;
 339         struct xfrm_sec_ctx *ctx = xp->security;
 340         int rc = 0;
 341
 342         if (ctx)
 343                 rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
 344                                   SECCLASS_ASSOCIATION,
 345                                   ASSOCIATION__SETCONTEXT, NULL);
 346
 347         return rc;
 348 }
 349
 350 /*
 351  * LSM hook implementation that allocs and transfers sec_ctx spec to
 352  * xfrm_state.
 353  */
 354 int selinux_xfrm_state_alloc(struct xfrm_state *x, struct xfrm_user_sec_ctx *uctx,
 355                 u32 secid)
 356 {
 357         int err;
 358
 359         BUG_ON(!x);
 360
 361         err = selinux_xfrm_sec_ctx_alloc(&x->security, uctx, secid);
 362         return err;
 363 }
 364
 365 /*
 366  * LSM hook implementation that frees xfrm_state security information.
 367  */
 368 void selinux_xfrm_state_free(struct xfrm_state *x)
 369 {
 370         struct xfrm_sec_ctx *ctx = x->security;
 371         if (ctx)
 372                 kfree(ctx);
 373 }
 374
 375  /*
 376   * LSM hook implementation that authorizes deletion of labeled SAs.
 377   */
 378 int selinux_xfrm_state_delete(struct xfrm_state *x)
 379 {
 380         struct task_security_struct *tsec = current->security;
 381         struct xfrm_sec_ctx *ctx = x->security;
 382         int rc = 0;
 383
 384         if (ctx)
 385                 rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
 386                                   SECCLASS_ASSOCIATION,
 387                                   ASSOCIATION__SETCONTEXT, NULL);
 388
 389         return rc;
 390 }
 391
 392 /*
 393  * LSM hook that controls access to unlabelled packets.  If
 394  * a xfrm_state is authorizable (defined by macro) then it was
 395  * already authorized by the IPSec process.  If not, then
 396  * we need to check for unlabelled access since this may not have
 397  * gone thru the IPSec process.
 398  */
 399 int selinux_xfrm_sock_rcv_skb(u32 isec_sid, struct sk_buff *skb,
 400                                 struct avc_audit_data *ad)
 401 {
 402         int i, rc = 0;
 403         struct sec_path *sp;
 404         u32 sel_sid = SECINITSID_UNLABELED;
 405
 406         sp = skb->sp;
 407
 408         if (sp) {
 409                 for (i = 0; i < sp->len; i++) {
 410                         struct xfrm_state *x = sp->xvec[i];
 411
 412                         if (x && selinux_authorizable_xfrm(x)) {
 413                                 struct xfrm_sec_ctx *ctx = x->security;
 414                                 sel_sid = ctx->ctx_sid;
 415                                 break;
 416                         }
 417                 }
 418         }
 419
 420         /*
 421          * This check even when there's no association involved is
 422          * intended, according to Trent Jaeger, to make sure a
 423          * process can't engage in non-ipsec communication unless
 424          * explicitly allowed by policy.
 425          */
 426
 427         rc = avc_has_perm(isec_sid, sel_sid, SECCLASS_ASSOCIATION,
 428                           ASSOCIATION__RECVFROM, ad);
 429
 430         return rc;
 431 }
 432
 433 /*
 434  * POSTROUTE_LAST hook's XFRM processing:
 435  * If we have no security association, then we need to determine
 436  * whether the socket is allowed to send to an unlabelled destination.
 437  * If we do have a authorizable security association, then it has already been
 438  * checked in the selinux_xfrm_state_pol_flow_match hook above.
 439  */
 440 int selinux_xfrm_postroute_last(u32 isec_sid, struct sk_buff *skb,
 441                                         struct avc_audit_data *ad, u8 proto)
 442 {
 443         struct dst_entry *dst;
 444         int rc = 0;
 445
 446         dst = skb->dst;
 447
 448         if (dst) {
 449                 struct dst_entry *dst_test;
 450
 451                 for (dst_test = dst; dst_test != 0;
 452                      dst_test = dst_test->child) {
 453                         struct xfrm_state *x = dst_test->xfrm;
 454
 455                         if (x && selinux_authorizable_xfrm(x))
 456                                 goto out;
 457                 }
 458         }
 459
 460         switch (proto) {
 461         case IPPROTO_AH:
 462         case IPPROTO_ESP:
 463         case IPPROTO_COMP:
 464                 /*
 465                  * We should have already seen this packet once before
 466                  * it underwent xfrm(s). No need to subject it to the
 467                  * unlabeled check.
 468                  */
 469                 goto out;
 470         default:
 471                 break;
 472         }
 473
 474         /*
 475          * This check even when there's no association involved is
 476          * intended, according to Trent Jaeger, to make sure a
 477          * process can't engage in non-ipsec communication unless
 478          * explicitly allowed by policy.
 479          */
 480
 481         rc = avc_has_perm(isec_sid, SECINITSID_UNLABELED, SECCLASS_ASSOCIATION,
 482                           ASSOCIATION__SENDTO, ad);
 483 out:
 484         return rc;
 485 }