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                                 }
 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         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         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_sec_ctx *ctx)
 337 {
 338         struct task_security_struct *tsec = current->security;
 339         int rc = 0;
 340
 341         if (ctx) {
 342                 rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
 343                                   SECCLASS_ASSOCIATION,
 344                                   ASSOCIATION__SETCONTEXT, NULL);
 345                 if (rc == 0)
 346                         atomic_dec(&selinux_xfrm_refcount);
 347         }
 348
 349         return rc;
 350 }
 351
 352 /*
 353  * LSM hook implementation that allocs and transfers sec_ctx spec to
 354  * xfrm_state.
 355  */
 356 int selinux_xfrm_state_alloc(struct xfrm_state *x, struct xfrm_user_sec_ctx *uctx,
 357                 u32 secid)
 358 {
 359         int err;
 360
 361         BUG_ON(!x);
 362
 363         err = selinux_xfrm_sec_ctx_alloc(&x->security, uctx, secid);
 364         if (err == 0)
 365                 atomic_inc(&selinux_xfrm_refcount);
 366         return err;
 367 }
 368
 369 /*
 370  * LSM hook implementation that frees xfrm_state security information.
 371  */
 372 void selinux_xfrm_state_free(struct xfrm_state *x)
 373 {
 374         struct xfrm_sec_ctx *ctx = x->security;
 375         if (ctx)
 376                 kfree(ctx);
 377 }
 378
 379  /*
 380   * LSM hook implementation that authorizes deletion of labeled SAs.
 381   */
 382 int selinux_xfrm_state_delete(struct xfrm_state *x)
 383 {
 384         struct task_security_struct *tsec = current->security;
 385         struct xfrm_sec_ctx *ctx = x->security;
 386         int rc = 0;
 387
 388         if (ctx) {
 389                 rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
 390                                   SECCLASS_ASSOCIATION,
 391                                   ASSOCIATION__SETCONTEXT, NULL);
 392                 if (rc == 0)
 393                         atomic_dec(&selinux_xfrm_refcount);
 394         }
 395
 396         return rc;
 397 }
 398
 399 /*
 400  * LSM hook that controls access to unlabelled packets.  If
 401  * a xfrm_state is authorizable (defined by macro) then it was
 402  * already authorized by the IPSec process.  If not, then
 403  * we need to check for unlabelled access since this may not have
 404  * gone thru the IPSec process.
 405  */
 406 int selinux_xfrm_sock_rcv_skb(u32 isec_sid, struct sk_buff *skb,
 407                                 struct avc_audit_data *ad)
 408 {
 409         int i, rc = 0;
 410         struct sec_path *sp;
 411         u32 sel_sid = SECINITSID_UNLABELED;
 412
 413         sp = skb->sp;
 414
 415         if (sp) {
 416                 for (i = 0; i < sp->len; i++) {
 417                         struct xfrm_state *x = sp->xvec[i];
 418
 419                         if (x && selinux_authorizable_xfrm(x)) {
 420                                 struct xfrm_sec_ctx *ctx = x->security;
 421                                 sel_sid = ctx->ctx_sid;
 422                                 break;
 423                         }
 424                 }
 425         }
 426
 427         /*
 428          * This check even when there's no association involved is
 429          * intended, according to Trent Jaeger, to make sure a
 430          * process can't engage in non-ipsec communication unless
 431          * explicitly allowed by policy.
 432          */
 433
 434         rc = avc_has_perm(isec_sid, sel_sid, SECCLASS_ASSOCIATION,
 435                           ASSOCIATION__RECVFROM, ad);
 436
 437         return rc;
 438 }
 439
 440 /*
 441  * POSTROUTE_LAST hook's XFRM processing:
 442  * If we have no security association, then we need to determine
 443  * whether the socket is allowed to send to an unlabelled destination.
 444  * If we do have a authorizable security association, then it has already been
 445  * checked in the selinux_xfrm_state_pol_flow_match hook above.
 446  */
 447 int selinux_xfrm_postroute_last(u32 isec_sid, struct sk_buff *skb,
 448                                         struct avc_audit_data *ad, u8 proto)
 449 {
 450         struct dst_entry *dst;
 451         int rc = 0;
 452
 453         dst = skb->dst;
 454
 455         if (dst) {
 456                 struct dst_entry *dst_test;
 457
 458                 for (dst_test = dst; dst_test != NULL;
 459                      dst_test = dst_test->child) {
 460                         struct xfrm_state *x = dst_test->xfrm;
 461
 462                         if (x && selinux_authorizable_xfrm(x))
 463                                 goto out;
 464                 }
 465         }
 466
 467         switch (proto) {
 468         case IPPROTO_AH:
 469         case IPPROTO_ESP:
 470         case IPPROTO_COMP:
 471                 /*
 472                  * We should have already seen this packet once before
 473                  * it underwent xfrm(s). No need to subject it to the
 474                  * unlabeled check.
 475                  */
 476                 goto out;
 477         default:
 478                 break;
 479         }
 480
 481         /*
 482          * This check even when there's no association involved is
 483          * intended, according to Trent Jaeger, to make sure a
 484          * process can't engage in non-ipsec communication unless
 485          * explicitly allowed by policy.
 486          */
 487
 488         rc = avc_has_perm(isec_sid, SECINITSID_UNLABELED, SECCLASS_ASSOCIATION,
 489                           ASSOCIATION__SENDTO, ad);
 490 out:
 491         return rc;
 492 }