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 #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                                 }
 185                                 else if (*sid != ctx->ctx_sid)
 186                                         return -EINVAL;
 187                         }
 188                 }
 189         }
 190
 191         return 0;
 192 }
 193
 194 /*
 195  * Security blob allocation for xfrm_policy and xfrm_state
 196  * CTX does not have a meaningful value on input
 197  */
 198 static int selinux_xfrm_sec_ctx_alloc(struct xfrm_sec_ctx **ctxp,
 199         struct xfrm_user_sec_ctx *uctx, u32 sid)
 200 {
 201         int rc = 0;
 202         struct task_security_struct *tsec = current->security;
 203         struct xfrm_sec_ctx *ctx = NULL;
 204         char *ctx_str = NULL;
 205         u32 str_len;
 206
 207         BUG_ON(uctx && sid);
 208
 209         if (!uctx)
 210                 goto not_from_user;
 211
 212         if (uctx->ctx_doi != XFRM_SC_ALG_SELINUX)
 213                 return -EINVAL;
 214
 215         str_len = uctx->ctx_len;
 216         if (str_len >= PAGE_SIZE)
 217                 return -ENOMEM;
 218
 219         *ctxp = ctx = kmalloc(sizeof(*ctx) +
 220                               str_len + 1,
 221                               GFP_KERNEL);
 222
 223         if (!ctx)
 224                 return -ENOMEM;
 225
 226         ctx->ctx_doi = uctx->ctx_doi;
 227         ctx->ctx_len = str_len;
 228         ctx->ctx_alg = uctx->ctx_alg;
 229
 230         memcpy(ctx->ctx_str,
 231                uctx+1,
 232                str_len);
 233         ctx->ctx_str[str_len] = 0;
 234         rc = security_context_to_sid(ctx->ctx_str,
 235                                      str_len,
 236                                      &ctx->ctx_sid);
 237
 238         if (rc)
 239                 goto out;
 240
 241         /*
 242          * Does the subject have permission to set security context?
 243          */
 244         rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
 245                           SECCLASS_ASSOCIATION,
 246                           ASSOCIATION__SETCONTEXT, NULL);
 247         if (rc)
 248                 goto out;
 249
 250         return rc;
 251
 252 not_from_user:
 253         rc = security_sid_to_context(sid, &ctx_str, &str_len);
 254         if (rc)
 255                 goto out;
 256
 257         *ctxp = ctx = kmalloc(sizeof(*ctx) +
 258                               str_len,
 259                               GFP_ATOMIC);
 260
 261         if (!ctx) {
 262                 rc = -ENOMEM;
 263                 goto out;
 264         }
 265
 266         ctx->ctx_doi = XFRM_SC_DOI_LSM;
 267         ctx->ctx_alg = XFRM_SC_ALG_SELINUX;
 268         ctx->ctx_sid = sid;
 269         ctx->ctx_len = str_len;
 270         memcpy(ctx->ctx_str,
 271                ctx_str,
 272                str_len);
 273
 274         goto out2;
 275
 276 out:
 277         *ctxp = NULL;
 278         kfree(ctx);
 279 out2:
 280         kfree(ctx_str);
 281         return rc;
 282 }
 283
 284 /*
 285  * LSM hook implementation that allocs and transfers uctx spec to
 286  * xfrm_policy.
 287  */
 288 int selinux_xfrm_policy_alloc(struct xfrm_sec_ctx **ctxp,
 289                               struct xfrm_user_sec_ctx *uctx)
 290 {
 291         int err;
 292
 293         BUG_ON(!uctx);
 294
 295         err = selinux_xfrm_sec_ctx_alloc(ctxp, uctx, 0);
 296         if (err == 0)
 297                 atomic_inc(&selinux_xfrm_refcount);
 298
 299         return err;
 300 }
 301
 302
 303 /*
 304  * LSM hook implementation that copies security data structure from old to
 305  * new for policy cloning.
 306  */
 307 int selinux_xfrm_policy_clone(struct xfrm_sec_ctx *old_ctx,
 308                               struct xfrm_sec_ctx **new_ctxp)
 309 {
 310         struct xfrm_sec_ctx *new_ctx;
 311
 312         if (old_ctx) {
 313                 new_ctx = kmalloc(sizeof(*old_ctx) + old_ctx->ctx_len,
 314                                   GFP_KERNEL);
 315                 if (!new_ctx)
 316                         return -ENOMEM;
 317
 318                 memcpy(new_ctx, old_ctx, sizeof(*new_ctx));
 319                 memcpy(new_ctx->ctx_str, old_ctx->ctx_str, new_ctx->ctx_len);
 320                 *new_ctxp = new_ctx;
 321         }
 322         return 0;
 323 }
 324
 325 /*
 326  * LSM hook implementation that frees xfrm_sec_ctx security information.
 327  */
 328 void selinux_xfrm_policy_free(struct xfrm_sec_ctx *ctx)
 329 {
 330         if (ctx)
 331                 kfree(ctx);
 332 }
 333
 334 /*
 335  * LSM hook implementation that authorizes deletion of labeled policies.
 336  */
 337 int selinux_xfrm_policy_delete(struct xfrm_sec_ctx *ctx)
 338 {
 339         struct task_security_struct *tsec = current->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                 if (rc == 0)
 347                         atomic_dec(&selinux_xfrm_refcount);
 348         }
 349
 350         return rc;
 351 }
 352
 353 /*
 354  * LSM hook implementation that allocs and transfers sec_ctx spec to
 355  * xfrm_state.
 356  */
 357 int selinux_xfrm_state_alloc(struct xfrm_state *x, struct xfrm_user_sec_ctx *uctx,
 358                 u32 secid)
 359 {
 360         int err;
 361
 362         BUG_ON(!x);
 363
 364         err = selinux_xfrm_sec_ctx_alloc(&x->security, uctx, secid);
 365         if (err == 0)
 366                 atomic_inc(&selinux_xfrm_refcount);
 367         return err;
 368 }
 369
 370 /*
 371  * LSM hook implementation that frees xfrm_state security information.
 372  */
 373 void selinux_xfrm_state_free(struct xfrm_state *x)
 374 {
 375         struct xfrm_sec_ctx *ctx = x->security;
 376         if (ctx)
 377                 kfree(ctx);
 378 }
 379
 380  /*
 381   * LSM hook implementation that authorizes deletion of labeled SAs.
 382   */
 383 int selinux_xfrm_state_delete(struct xfrm_state *x)
 384 {
 385         struct task_security_struct *tsec = current->security;
 386         struct xfrm_sec_ctx *ctx = x->security;
 387         int rc = 0;
 388
 389         if (ctx) {
 390                 rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
 391                                   SECCLASS_ASSOCIATION,
 392                                   ASSOCIATION__SETCONTEXT, NULL);
 393                 if (rc == 0)
 394                         atomic_dec(&selinux_xfrm_refcount);
 395         }
 396
 397         return rc;
 398 }
 399
 400 /*
 401  * LSM hook that controls access to unlabelled packets.  If
 402  * a xfrm_state is authorizable (defined by macro) then it was
 403  * already authorized by the IPSec process.  If not, then
 404  * we need to check for unlabelled access since this may not have
 405  * gone thru the IPSec process.
 406  */
 407 int selinux_xfrm_sock_rcv_skb(u32 isec_sid, struct sk_buff *skb,
 408                                 struct avc_audit_data *ad)
 409 {
 410         int i, rc = 0;
 411         struct sec_path *sp;
 412         u32 sel_sid = SECINITSID_UNLABELED;
 413
 414         sp = skb->sp;
 415
 416         if (sp) {
 417                 for (i = 0; i < sp->len; i++) {
 418                         struct xfrm_state *x = sp->xvec[i];
 419
 420                         if (x && selinux_authorizable_xfrm(x)) {
 421                                 struct xfrm_sec_ctx *ctx = x->security;
 422                                 sel_sid = ctx->ctx_sid;
 423                                 break;
 424                         }
 425                 }
 426         }
 427
 428         /*
 429          * This check even when there's no association involved is
 430          * intended, according to Trent Jaeger, to make sure a
 431          * process can't engage in non-ipsec communication unless
 432          * explicitly allowed by policy.
 433          */
 434
 435         rc = avc_has_perm(isec_sid, sel_sid, SECCLASS_ASSOCIATION,
 436                           ASSOCIATION__RECVFROM, ad);
 437
 438         return rc;
 439 }
 440
 441 /*
 442  * POSTROUTE_LAST hook's XFRM processing:
 443  * If we have no security association, then we need to determine
 444  * whether the socket is allowed to send to an unlabelled destination.
 445  * If we do have a authorizable security association, then it has already been
 446  * checked in the selinux_xfrm_state_pol_flow_match hook above.
 447  */
 448 int selinux_xfrm_postroute_last(u32 isec_sid, struct sk_buff *skb,
 449                                         struct avc_audit_data *ad, u8 proto)
 450 {
 451         struct dst_entry *dst;
 452         int rc = 0;
 453
 454         dst = skb->dst;
 455
 456         if (dst) {
 457                 struct dst_entry *dst_test;
 458
 459                 for (dst_test = dst; dst_test != NULL;
 460                      dst_test = dst_test->child) {
 461                         struct xfrm_state *x = dst_test->xfrm;
 462
 463                         if (x && selinux_authorizable_xfrm(x))
 464                                 goto out;
 465                 }
 466         }
 467
 468         switch (proto) {
 469         case IPPROTO_AH:
 470         case IPPROTO_ESP:
 471         case IPPROTO_COMP:
 472                 /*
 473                  * We should have already seen this packet once before
 474                  * it underwent xfrm(s). No need to subject it to the
 475                  * unlabeled check.
 476                  */
 477                 goto out;
 478         default:
 479                 break;
 480         }
 481
 482         /*
 483          * This check even when there's no association involved is
 484          * intended, according to Trent Jaeger, to make sure a
 485          * process can't engage in non-ipsec communication unless
 486          * explicitly allowed by policy.
 487          */
 488
 489         rc = avc_has_perm(isec_sid, SECINITSID_UNLABELED, SECCLASS_ASSOCIATION,
 490                           ASSOCIATION__SENDTO, ad);
 491 out:
 492         return rc;
 493 }