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_policy *xp, u32 fl_secid, u8 dir)
  81 {
  82         int rc;
  83         u32 sel_sid;
  84         struct xfrm_sec_ctx *ctx;
  85
  86         /* Context sid is either set to label or ANY_ASSOC */
  87         if ((ctx = xp->security)) {
  88                 if (!selinux_authorizable_ctx(ctx))
  89                         return -EINVAL;
  90
  91                 sel_sid = ctx->ctx_sid;
  92         }
  93         else
  94                 /*
  95                  * All flows should be treated as polmatch'ing an
  96                  * otherwise applicable "non-labeled" policy. This
  97                  * would prevent inadvertent "leaks".
  98                  */
  99                 return 0;
 100
 101         rc = avc_has_perm(fl_secid, sel_sid, SECCLASS_ASSOCIATION,
 102                           ASSOCIATION__POLMATCH,
 103                           NULL);
 104
 105         if (rc == -EACCES)
 106                 rc = -ESRCH;
 107
 108         return rc;
 109 }
 110
 111 /*
 112  * LSM hook implementation that authorizes that a state matches
 113  * the given policy, flow combo.
 114  */
 115
 116 int selinux_xfrm_state_pol_flow_match(struct xfrm_state *x, struct xfrm_policy *xp,
 117                         struct flowi *fl)
 118 {
 119         u32 state_sid;
 120         int rc;
 121
 122         if (!xp->security)
 123                 if (x->security)
 124                         /* unlabeled policy and labeled SA can't match */
 125                         return 0;
 126                 else
 127                         /* unlabeled policy and unlabeled SA match all flows */
 128                         return 1;
 129         else
 130                 if (!x->security)
 131                         /* unlabeled SA and labeled policy can't match */
 132                         return 0;
 133                 else
 134                         if (!selinux_authorizable_xfrm(x))
 135                                 /* Not a SELinux-labeled SA */
 136                                 return 0;
 137
 138         state_sid = x->security->ctx_sid;
 139
 140         if (fl->secid != state_sid)
 141                 return 0;
 142
 143         rc = avc_has_perm(fl->secid, state_sid, SECCLASS_ASSOCIATION,
 144                           ASSOCIATION__SENDTO,
 145                           NULL)? 0:1;
 146
 147         /*
 148          * We don't need a separate SA Vs. policy polmatch check
 149          * since the SA is now of the same label as the flow and
 150          * a flow Vs. policy polmatch check had already happened
 151          * in selinux_xfrm_policy_lookup() above.
 152          */
 153
 154         return rc;
 155 }
 156
 157 /*
 158  * LSM hook implementation that checks and/or returns the xfrm sid for the
 159  * incoming packet.
 160  */
 161
 162 int selinux_xfrm_decode_session(struct sk_buff *skb, u32 *sid, int ckall)
 163 {
 164         struct sec_path *sp;
 165
 166         *sid = SECSID_NULL;
 167
 168         if (skb == NULL)
 169                 return 0;
 170
 171         sp = skb->sp;
 172         if (sp) {
 173                 int i, sid_set = 0;
 174
 175                 for (i = sp->len-1; i >= 0; i--) {
 176                         struct xfrm_state *x = sp->xvec[i];
 177                         if (selinux_authorizable_xfrm(x)) {
 178                                 struct xfrm_sec_ctx *ctx = x->security;
 179
 180                                 if (!sid_set) {
 181                                         *sid = ctx->ctx_sid;
 182                                         sid_set = 1;
 183
 184                                         if (!ckall)
 185                                                 break;
 186                                 }
 187                                 else if (*sid != ctx->ctx_sid)
 188                                         return -EINVAL;
 189                         }
 190                 }
 191         }
 192
 193         return 0;
 194 }
 195
 196 /*
 197  * Security blob allocation for xfrm_policy and xfrm_state
 198  * CTX does not have a meaningful value on input
 199  */
 200 static int selinux_xfrm_sec_ctx_alloc(struct xfrm_sec_ctx **ctxp,
 201         struct xfrm_user_sec_ctx *uctx, u32 sid)
 202 {
 203         int rc = 0;
 204         struct task_security_struct *tsec = current->security;
 205         struct xfrm_sec_ctx *ctx = NULL;
 206         char *ctx_str = NULL;
 207         u32 str_len;
 208
 209         BUG_ON(uctx && sid);
 210
 211         if (!uctx)
 212                 goto not_from_user;
 213
 214         if (uctx->ctx_doi != XFRM_SC_ALG_SELINUX)
 215                 return -EINVAL;
 216
 217         str_len = uctx->ctx_len;
 218         if (str_len >= PAGE_SIZE)
 219                 return -ENOMEM;
 220
 221         *ctxp = ctx = kmalloc(sizeof(*ctx) +
 222                               str_len + 1,
 223                               GFP_KERNEL);
 224
 225         if (!ctx)
 226                 return -ENOMEM;
 227
 228         ctx->ctx_doi = uctx->ctx_doi;
 229         ctx->ctx_len = str_len;
 230         ctx->ctx_alg = uctx->ctx_alg;
 231
 232         memcpy(ctx->ctx_str,
 233                uctx+1,
 234                str_len);
 235         ctx->ctx_str[str_len] = 0;
 236         rc = security_context_to_sid(ctx->ctx_str,
 237                                      str_len,
 238                                      &ctx->ctx_sid);
 239
 240         if (rc)
 241                 goto out;
 242
 243         /*
 244          * Does the subject have permission to set security context?
 245          */
 246         rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
 247                           SECCLASS_ASSOCIATION,
 248                           ASSOCIATION__SETCONTEXT, NULL);
 249         if (rc)
 250                 goto out;
 251
 252         return rc;
 253
 254 not_from_user:
 255         rc = security_sid_to_context(sid, &ctx_str, &str_len);
 256         if (rc)
 257                 goto out;
 258
 259         *ctxp = ctx = kmalloc(sizeof(*ctx) +
 260                               str_len,
 261                               GFP_ATOMIC);
 262
 263         if (!ctx) {
 264                 rc = -ENOMEM;
 265                 goto out;
 266         }
 267
 268         ctx->ctx_doi = XFRM_SC_DOI_LSM;
 269         ctx->ctx_alg = XFRM_SC_ALG_SELINUX;
 270         ctx->ctx_sid = sid;
 271         ctx->ctx_len = str_len;
 272         memcpy(ctx->ctx_str,
 273                ctx_str,
 274                str_len);
 275
 276         goto out2;
 277
 278 out:
 279         *ctxp = NULL;
 280         kfree(ctx);
 281 out2:
 282         kfree(ctx_str);
 283         return rc;
 284 }
 285
 286 /*
 287  * LSM hook implementation that allocs and transfers uctx spec to
 288  * xfrm_policy.
 289  */
 290 int selinux_xfrm_policy_alloc(struct xfrm_policy *xp,
 291                 struct xfrm_user_sec_ctx *uctx)
 292 {
 293         int err;
 294
 295         BUG_ON(!xp);
 296         BUG_ON(!uctx);
 297
 298         err = selinux_xfrm_sec_ctx_alloc(&xp->security, uctx, 0);
 299         if (err == 0)
 300                 atomic_inc(&selinux_xfrm_refcount);
 301
 302         return err;
 303 }
 304
 305
 306 /*
 307  * LSM hook implementation that copies security data structure from old to
 308  * new for policy cloning.
 309  */
 310 int selinux_xfrm_policy_clone(struct xfrm_policy *old, struct xfrm_policy *new)
 311 {
 312         struct xfrm_sec_ctx *old_ctx, *new_ctx;
 313
 314         old_ctx = old->security;
 315
 316         if (old_ctx) {
 317                 new_ctx = new->security = kmalloc(sizeof(*new_ctx) +
 318                                                   old_ctx->ctx_len,
 319                                                   GFP_KERNEL);
 320
 321                 if (!new_ctx)
 322                         return -ENOMEM;
 323
 324                 memcpy(new_ctx, old_ctx, sizeof(*new_ctx));
 325                 memcpy(new_ctx->ctx_str, old_ctx->ctx_str, new_ctx->ctx_len);
 326         }
 327         return 0;
 328 }
 329
 330 /*
 331  * LSM hook implementation that frees xfrm_policy security information.
 332  */
 333 void selinux_xfrm_policy_free(struct xfrm_policy *xp)
 334 {
 335         struct xfrm_sec_ctx *ctx = xp->security;
 336         if (ctx)
 337                 kfree(ctx);
 338 }
 339
 340 /*
 341  * LSM hook implementation that authorizes deletion of labeled policies.
 342  */
 343 int selinux_xfrm_policy_delete(struct xfrm_policy *xp)
 344 {
 345         struct task_security_struct *tsec = current->security;
 346         struct xfrm_sec_ctx *ctx = xp->security;
 347         int rc = 0;
 348
 349         if (ctx) {
 350                 rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
 351                                   SECCLASS_ASSOCIATION,
 352                                   ASSOCIATION__SETCONTEXT, NULL);
 353                 if (rc == 0)
 354                         atomic_dec(&selinux_xfrm_refcount);
 355         }
 356
 357         return rc;
 358 }
 359
 360 /*
 361  * LSM hook implementation that allocs and transfers sec_ctx spec to
 362  * xfrm_state.
 363  */
 364 int selinux_xfrm_state_alloc(struct xfrm_state *x, struct xfrm_user_sec_ctx *uctx,
 365                 u32 secid)
 366 {
 367         int err;
 368
 369         BUG_ON(!x);
 370
 371         err = selinux_xfrm_sec_ctx_alloc(&x->security, uctx, secid);
 372         if (err == 0)
 373                 atomic_inc(&selinux_xfrm_refcount);
 374         return err;
 375 }
 376
 377 /*
 378  * LSM hook implementation that frees xfrm_state security information.
 379  */
 380 void selinux_xfrm_state_free(struct xfrm_state *x)
 381 {
 382         struct xfrm_sec_ctx *ctx = x->security;
 383         if (ctx)
 384                 kfree(ctx);
 385 }
 386
 387  /*
 388   * LSM hook implementation that authorizes deletion of labeled SAs.
 389   */
 390 int selinux_xfrm_state_delete(struct xfrm_state *x)
 391 {
 392         struct task_security_struct *tsec = current->security;
 393         struct xfrm_sec_ctx *ctx = x->security;
 394         int rc = 0;
 395
 396         if (ctx) {
 397                 rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
 398                                   SECCLASS_ASSOCIATION,
 399                                   ASSOCIATION__SETCONTEXT, NULL);
 400                 if (rc == 0)
 401                         atomic_dec(&selinux_xfrm_refcount);
 402         }
 403
 404         return rc;
 405 }
 406
 407 /*
 408  * LSM hook that controls access to unlabelled packets.  If
 409  * a xfrm_state is authorizable (defined by macro) then it was
 410  * already authorized by the IPSec process.  If not, then
 411  * we need to check for unlabelled access since this may not have
 412  * gone thru the IPSec process.
 413  */
 414 int selinux_xfrm_sock_rcv_skb(u32 isec_sid, struct sk_buff *skb,
 415                                 struct avc_audit_data *ad)
 416 {
 417         int i, rc = 0;
 418         struct sec_path *sp;
 419         u32 sel_sid = SECINITSID_UNLABELED;
 420
 421         sp = skb->sp;
 422
 423         if (sp) {
 424                 for (i = 0; i < sp->len; i++) {
 425                         struct xfrm_state *x = sp->xvec[i];
 426
 427                         if (x && selinux_authorizable_xfrm(x)) {
 428                                 struct xfrm_sec_ctx *ctx = x->security;
 429                                 sel_sid = ctx->ctx_sid;
 430                                 break;
 431                         }
 432                 }
 433         }
 434
 435         /*
 436          * This check even when there's no association involved is
 437          * intended, according to Trent Jaeger, to make sure a
 438          * process can't engage in non-ipsec communication unless
 439          * explicitly allowed by policy.
 440          */
 441
 442         rc = avc_has_perm(isec_sid, sel_sid, SECCLASS_ASSOCIATION,
 443                           ASSOCIATION__RECVFROM, ad);
 444
 445         return rc;
 446 }
 447
 448 /*
 449  * POSTROUTE_LAST hook's XFRM processing:
 450  * If we have no security association, then we need to determine
 451  * whether the socket is allowed to send to an unlabelled destination.
 452  * If we do have a authorizable security association, then it has already been
 453  * checked in the selinux_xfrm_state_pol_flow_match hook above.
 454  */
 455 int selinux_xfrm_postroute_last(u32 isec_sid, struct sk_buff *skb,
 456                                         struct avc_audit_data *ad, u8 proto)
 457 {
 458         struct dst_entry *dst;
 459         int rc = 0;
 460
 461         dst = skb->dst;
 462
 463         if (dst) {
 464                 struct dst_entry *dst_test;
 465
 466                 for (dst_test = dst; dst_test != NULL;
 467                      dst_test = dst_test->child) {
 468                         struct xfrm_state *x = dst_test->xfrm;
 469
 470                         if (x && selinux_authorizable_xfrm(x))
 471                                 goto out;
 472                 }
 473         }
 474
 475         switch (proto) {
 476         case IPPROTO_AH:
 477         case IPPROTO_ESP:
 478         case IPPROTO_COMP:
 479                 /*
 480                  * We should have already seen this packet once before
 481                  * it underwent xfrm(s). No need to subject it to the
 482                  * unlabeled check.
 483                  */
 484                 goto out;
 485         default:
 486                 break;
 487         }
 488
 489         /*
 490          * This check even when there's no association involved is
 491          * intended, according to Trent Jaeger, to make sure a
 492          * process can't engage in non-ipsec communication unless
 493          * explicitly allowed by policy.
 494          */
 495
 496         rc = avc_has_perm(isec_sid, SECINITSID_UNLABELED, SECCLASS_ASSOCIATION,
 497                           ASSOCIATION__SENDTO, ad);
 498 out:
 499         return rc;
 500 }