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/atomic.h>
  49
  50 #include "avc.h"
  51 #include "objsec.h"
  52 #include "xfrm.h"
  53
  54 /* Labeled XFRM instance counter */
  55 atomic_t selinux_xfrm_refcount = ATOMIC_INIT(0);
  56
  57 /*
  58  * Returns true if an LSM/SELinux context
  59  */
  60 static inline int selinux_authorizable_ctx(struct xfrm_sec_ctx *ctx)
  61 {
  62         return (ctx &&
  63                 (ctx->ctx_doi == XFRM_SC_DOI_LSM) &&
  64                 (ctx->ctx_alg == XFRM_SC_ALG_SELINUX));
  65 }
  66
  67 /*
  68  * Returns true if the xfrm contains a security blob for SELinux
  69  */
  70 static inline int selinux_authorizable_xfrm(struct xfrm_state *x)
  71 {
  72         return selinux_authorizable_ctx(x->security);
  73 }
  74
  75 /*
  76  * LSM hook implementation that authorizes that a flow can use
  77  * a xfrm policy rule.
  78  */
  79 int selinux_xfrm_policy_lookup(struct xfrm_sec_ctx *ctx, u32 fl_secid, u8 dir)
  80 {
  81         int rc;
  82         u32 sel_sid;
  83
  84         /* Context sid is either set to label or ANY_ASSOC */
  85         if (ctx) {
  86                 if (!selinux_authorizable_ctx(ctx))
  87                         return -EINVAL;
  88
  89                 sel_sid = ctx->ctx_sid;
  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                 return -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                                 } else if (*sid != ctx->ctx_sid)
 184                                         return -EINVAL;
 185                         }
 186                 }
 187         }
 188
 189         return 0;
 190 }
 191
 192 /*
 193  * Security blob allocation for xfrm_policy and xfrm_state
 194  * CTX does not have a meaningful value on input
 195  */
 196 static int selinux_xfrm_sec_ctx_alloc(struct xfrm_sec_ctx **ctxp,
 197         struct xfrm_user_sec_ctx *uctx, u32 sid)
 198 {
 199         int rc = 0;
 200         const struct task_security_struct *tsec = current_security();
 201         struct xfrm_sec_ctx *ctx = NULL;
 202         char *ctx_str = NULL;
 203         u32 str_len;
 204
 205         BUG_ON(uctx && sid);
 206
 207         if (!uctx)
 208                 goto not_from_user;
 209
 210         if (uctx->ctx_doi != XFRM_SC_ALG_SELINUX)
 211                 return -EINVAL;
 212
 213         str_len = uctx->ctx_len;
 214         if (str_len >= PAGE_SIZE)
 215                 return -ENOMEM;
 216
 217         *ctxp = ctx = kmalloc(sizeof(*ctx) +
 218                               str_len + 1,
 219                               GFP_KERNEL);
 220
 221         if (!ctx)
 222                 return -ENOMEM;
 223
 224         ctx->ctx_doi = uctx->ctx_doi;
 225         ctx->ctx_len = str_len;
 226         ctx->ctx_alg = uctx->ctx_alg;
 227
 228         memcpy(ctx->ctx_str,
 229                uctx+1,
 230                str_len);
 231         ctx->ctx_str[str_len] = 0;
 232         rc = security_context_to_sid(ctx->ctx_str,
 233                                      str_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_sec_ctx **ctxp,
 287                               struct xfrm_user_sec_ctx *uctx)
 288 {
 289         int err;
 290
 291         BUG_ON(!uctx);
 292
 293         err = selinux_xfrm_sec_ctx_alloc(ctxp, uctx, 0);
 294         if (err == 0)
 295                 atomic_inc(&selinux_xfrm_refcount);
 296
 297         return err;
 298 }
 299
 300
 301 /*
 302  * LSM hook implementation that copies security data structure from old to
 303  * new for policy cloning.
 304  */
 305 int selinux_xfrm_policy_clone(struct xfrm_sec_ctx *old_ctx,
 306                               struct xfrm_sec_ctx **new_ctxp)
 307 {
 308         struct xfrm_sec_ctx *new_ctx;
 309
 310         if (old_ctx) {
 311                 new_ctx = kmalloc(sizeof(*old_ctx) + old_ctx->ctx_len,
 312                                   GFP_KERNEL);
 313                 if (!new_ctx)
 314                         return -ENOMEM;
 315
 316                 memcpy(new_ctx, old_ctx, sizeof(*new_ctx));
 317                 memcpy(new_ctx->ctx_str, old_ctx->ctx_str, new_ctx->ctx_len);
 318                 *new_ctxp = new_ctx;
 319         }
 320         return 0;
 321 }
 322
 323 /*
 324  * LSM hook implementation that frees xfrm_sec_ctx security information.
 325  */
 326 void selinux_xfrm_policy_free(struct xfrm_sec_ctx *ctx)
 327 {
 328         kfree(ctx);
 329 }
 330
 331 /*
 332  * LSM hook implementation that authorizes deletion of labeled policies.
 333  */
 334 int selinux_xfrm_policy_delete(struct xfrm_sec_ctx *ctx)
 335 {
 336         const struct task_security_struct *tsec = current_security();
 337         int rc = 0;
 338
 339         if (ctx) {
 340                 rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
 341                                   SECCLASS_ASSOCIATION,
 342                                   ASSOCIATION__SETCONTEXT, NULL);
 343                 if (rc == 0)
 344                         atomic_dec(&selinux_xfrm_refcount);
 345         }
 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         if (err == 0)
 363                 atomic_inc(&selinux_xfrm_refcount);
 364         return err;
 365 }
 366
 367 /*
 368  * LSM hook implementation that frees xfrm_state security information.
 369  */
 370 void selinux_xfrm_state_free(struct xfrm_state *x)
 371 {
 372         struct xfrm_sec_ctx *ctx = x->security;
 373         kfree(ctx);
 374 }
 375
 376  /*
 377   * LSM hook implementation that authorizes deletion of labeled SAs.
 378   */
 379 int selinux_xfrm_state_delete(struct xfrm_state *x)
 380 {
 381         const struct task_security_struct *tsec = current_security();
 382         struct xfrm_sec_ctx *ctx = x->security;
 383         int rc = 0;
 384
 385         if (ctx) {
 386                 rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
 387                                   SECCLASS_ASSOCIATION,
 388                                   ASSOCIATION__SETCONTEXT, NULL);
 389                 if (rc == 0)
 390                         atomic_dec(&selinux_xfrm_refcount);
 391         }
 392
 393         return rc;
 394 }
 395
 396 /*
 397  * LSM hook that controls access to unlabelled packets.  If
 398  * a xfrm_state is authorizable (defined by macro) then it was
 399  * already authorized by the IPSec process.  If not, then
 400  * we need to check for unlabelled access since this may not have
 401  * gone thru the IPSec process.
 402  */
 403 int selinux_xfrm_sock_rcv_skb(u32 isec_sid, struct sk_buff *skb,
 404                                 struct common_audit_data *ad)
 405 {
 406         int i, rc = 0;
 407         struct sec_path *sp;
 408         u32 sel_sid = SECINITSID_UNLABELED;
 409
 410         sp = skb->sp;
 411
 412         if (sp) {
 413                 for (i = 0; i < sp->len; i++) {
 414                         struct xfrm_state *x = sp->xvec[i];
 415
 416                         if (x && selinux_authorizable_xfrm(x)) {
 417                                 struct xfrm_sec_ctx *ctx = x->security;
 418                                 sel_sid = ctx->ctx_sid;
 419                                 break;
 420                         }
 421                 }
 422         }
 423
 424         /*
 425          * This check even when there's no association involved is
 426          * intended, according to Trent Jaeger, to make sure a
 427          * process can't engage in non-ipsec communication unless
 428          * explicitly allowed by policy.
 429          */
 430
 431         rc = avc_has_perm(isec_sid, sel_sid, SECCLASS_ASSOCIATION,
 432                           ASSOCIATION__RECVFROM, ad);
 433
 434         return rc;
 435 }
 436
 437 /*
 438  * POSTROUTE_LAST hook's XFRM processing:
 439  * If we have no security association, then we need to determine
 440  * whether the socket is allowed to send to an unlabelled destination.
 441  * If we do have a authorizable security association, then it has already been
 442  * checked in the selinux_xfrm_state_pol_flow_match hook above.
 443  */
 444 int selinux_xfrm_postroute_last(u32 isec_sid, struct sk_buff *skb,
 445                                         struct common_audit_data *ad, u8 proto)
 446 {
 447         struct dst_entry *dst;
 448         int rc = 0;
 449
 450         dst = skb_dst(skb);
 451
 452         if (dst) {
 453                 struct dst_entry *dst_test;
 454
 455                 for (dst_test = dst; dst_test != NULL;
 456                      dst_test = dst_test->child) {
 457                         struct xfrm_state *x = dst_test->xfrm;
 458
 459                         if (x && selinux_authorizable_xfrm(x))
 460                                 goto out;
 461                 }
 462         }
 463
 464         switch (proto) {
 465         case IPPROTO_AH:
 466         case IPPROTO_ESP:
 467         case IPPROTO_COMP:
 468                 /*
 469                  * We should have already seen this packet once before
 470                  * it underwent xfrm(s). No need to subject it to the
 471                  * unlabeled check.
 472                  */
 473                 goto out;
 474         default:
 475                 break;
 476         }
 477
 478         /*
 479          * This check even when there's no association involved is
 480          * intended, according to Trent Jaeger, to make sure a
 481          * process can't engage in non-ipsec communication unless
 482          * explicitly allowed by policy.
 483          */
 484
 485         rc = avc_has_perm(isec_sid, SECINITSID_UNLABELED, SECCLASS_ASSOCIATION,
 486                           ASSOCIATION__SENDTO, ad);
 487 out:
 488         return rc;
 489 }