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/slab.h>
  39 #include <linux/ip.h>
  40 #include <linux/tcp.h>
  41 #include <linux/skbuff.h>
  42 #include <linux/xfrm.h>
  43 #include <net/xfrm.h>
  44 #include <net/checksum.h>
  45 #include <net/udp.h>
  46 #include <linux/atomic.h>
  47
  48 #include "avc.h"
  49 #include "objsec.h"
  50 #include "xfrm.h"
  51
  52 /* Labeled XFRM instance counter */
  53 atomic_t selinux_xfrm_refcount = ATOMIC_INIT(0);
  54
  55 /*
  56  * Returns true if the context is 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  * Allocates a xfrm_sec_state and populates it using the supplied security
  75  * xfrm_user_sec_ctx context.
  76  */
  77 static int selinux_xfrm_alloc_user(struct xfrm_sec_ctx **ctxp,
  78                                    struct xfrm_user_sec_ctx *uctx,
  79                                    gfp_t gfp)
  80 {
  81         int rc;
  82         const struct task_security_struct *tsec = selinux_cred(current_cred());
  83         struct xfrm_sec_ctx *ctx = NULL;
  84         u32 str_len;
  85
  86         if (ctxp == NULL || uctx == NULL ||
  87             uctx->ctx_doi != XFRM_SC_DOI_LSM ||
  88             uctx->ctx_alg != XFRM_SC_ALG_SELINUX)
  89                 return -EINVAL;
  90
  91         str_len = uctx->ctx_len;
  92         if (str_len >= PAGE_SIZE)
  93                 return -ENOMEM;
  94
  95         ctx = kmalloc(sizeof(*ctx) + str_len + 1, gfp);
  96         if (!ctx)
  97                 return -ENOMEM;
  98
  99         ctx->ctx_doi = XFRM_SC_DOI_LSM;
 100         ctx->ctx_alg = XFRM_SC_ALG_SELINUX;
 101         ctx->ctx_len = str_len;
 102         memcpy(ctx->ctx_str, &uctx[1], str_len);
 103         ctx->ctx_str[str_len] = '\0';
 104         rc = security_context_to_sid(&selinux_state, ctx->ctx_str, str_len,
 105                                      &ctx->ctx_sid, gfp);
 106         if (rc)
 107                 goto err;
 108
 109         rc = avc_has_perm(&selinux_state,
 110                           tsec->sid, ctx->ctx_sid,
 111                           SECCLASS_ASSOCIATION, ASSOCIATION__SETCONTEXT, NULL);
 112         if (rc)
 113                 goto err;
 114
 115         *ctxp = ctx;
 116         atomic_inc(&selinux_xfrm_refcount);
 117         return 0;
 118
 119 err:
 120         kfree(ctx);
 121         return rc;
 122 }
 123
 124 /*
 125  * Free the xfrm_sec_ctx structure.
 126  */
 127 static void selinux_xfrm_free(struct xfrm_sec_ctx *ctx)
 128 {
 129         if (!ctx)
 130                 return;
 131
 132         atomic_dec(&selinux_xfrm_refcount);
 133         kfree(ctx);
 134 }
 135
 136 /*
 137  * Authorize the deletion of a labeled SA or policy rule.
 138  */
 139 static int selinux_xfrm_delete(struct xfrm_sec_ctx *ctx)
 140 {
 141         const struct task_security_struct *tsec = selinux_cred(current_cred());
 142
 143         if (!ctx)
 144                 return 0;
 145
 146         return avc_has_perm(&selinux_state,
 147                             tsec->sid, ctx->ctx_sid,
 148                             SECCLASS_ASSOCIATION, ASSOCIATION__SETCONTEXT,
 149                             NULL);
 150 }
 151
 152 /*
 153  * LSM hook implementation that authorizes that a flow can use a xfrm policy
 154  * rule.
 155  */
 156 int selinux_xfrm_policy_lookup(struct xfrm_sec_ctx *ctx, u32 fl_secid, u8 dir)
 157 {
 158         int rc;
 159
 160         /* All flows should be treated as polmatch'ing an otherwise applicable
 161          * "non-labeled" policy. This would prevent inadvertent "leaks". */
 162         if (!ctx)
 163                 return 0;
 164
 165         /* Context sid is either set to label or ANY_ASSOC */
 166         if (!selinux_authorizable_ctx(ctx))
 167                 return -EINVAL;
 168
 169         rc = avc_has_perm(&selinux_state,
 170                           fl_secid, ctx->ctx_sid,
 171                           SECCLASS_ASSOCIATION, ASSOCIATION__POLMATCH, NULL);
 172         return (rc == -EACCES ? -ESRCH : rc);
 173 }
 174
 175 /*
 176  * LSM hook implementation that authorizes that a state matches
 177  * the given policy, flow combo.
 178  */
 179 int selinux_xfrm_state_pol_flow_match(struct xfrm_state *x,
 180                                       struct xfrm_policy *xp,
 181                                       const struct flowi *fl)
 182 {
 183         u32 state_sid;
 184
 185         if (!xp->security)
 186                 if (x->security)
 187                         /* unlabeled policy and labeled SA can't match */
 188                         return 0;
 189                 else
 190                         /* unlabeled policy and unlabeled SA match all flows */
 191                         return 1;
 192         else
 193                 if (!x->security)
 194                         /* unlabeled SA and labeled policy can't match */
 195                         return 0;
 196                 else
 197                         if (!selinux_authorizable_xfrm(x))
 198                                 /* Not a SELinux-labeled SA */
 199                                 return 0;
 200
 201         state_sid = x->security->ctx_sid;
 202
 203         if (fl->flowi_secid != state_sid)
 204                 return 0;
 205
 206         /* We don't need a separate SA Vs. policy polmatch check since the SA
 207          * is now of the same label as the flow and a flow Vs. policy polmatch
 208          * check had already happened in selinux_xfrm_policy_lookup() above. */
 209         return (avc_has_perm(&selinux_state,
 210                              fl->flowi_secid, state_sid,
 211                             SECCLASS_ASSOCIATION, ASSOCIATION__SENDTO,
 212                             NULL) ? 0 : 1);
 213 }
 214
 215 static u32 selinux_xfrm_skb_sid_egress(struct sk_buff *skb)
 216 {
 217         struct dst_entry *dst = skb_dst(skb);
 218         struct xfrm_state *x;
 219
 220         if (dst == NULL)
 221                 return SECSID_NULL;
 222         x = dst->xfrm;
 223         if (x == NULL || !selinux_authorizable_xfrm(x))
 224                 return SECSID_NULL;
 225
 226         return x->security->ctx_sid;
 227 }
 228
 229 static int selinux_xfrm_skb_sid_ingress(struct sk_buff *skb,
 230                                         u32 *sid, int ckall)
 231 {
 232         u32 sid_session = SECSID_NULL;
 233         struct sec_path *sp = skb_sec_path(skb);
 234
 235         if (sp) {
 236                 int i;
 237
 238                 for (i = sp->len - 1; i >= 0; i--) {
 239                         struct xfrm_state *x = sp->xvec[i];
 240                         if (selinux_authorizable_xfrm(x)) {
 241                                 struct xfrm_sec_ctx *ctx = x->security;
 242
 243                                 if (sid_session == SECSID_NULL) {
 244                                         sid_session = ctx->ctx_sid;
 245                                         if (!ckall)
 246                                                 goto out;
 247                                 } else if (sid_session != ctx->ctx_sid) {
 248                                         *sid = SECSID_NULL;
 249                                         return -EINVAL;
 250                                 }
 251                         }
 252                 }
 253         }
 254
 255 out:
 256         *sid = sid_session;
 257         return 0;
 258 }
 259
 260 /*
 261  * LSM hook implementation that checks and/or returns the xfrm sid for the
 262  * incoming packet.
 263  */
 264 int selinux_xfrm_decode_session(struct sk_buff *skb, u32 *sid, int ckall)
 265 {
 266         if (skb == NULL) {
 267                 *sid = SECSID_NULL;
 268                 return 0;
 269         }
 270         return selinux_xfrm_skb_sid_ingress(skb, sid, ckall);
 271 }
 272
 273 int selinux_xfrm_skb_sid(struct sk_buff *skb, u32 *sid)
 274 {
 275         int rc;
 276
 277         rc = selinux_xfrm_skb_sid_ingress(skb, sid, 0);
 278         if (rc == 0 && *sid == SECSID_NULL)
 279                 *sid = selinux_xfrm_skb_sid_egress(skb);
 280
 281         return rc;
 282 }
 283
 284 /*
 285  * LSM hook implementation that allocs and transfers uctx spec to xfrm_policy.
 286  */
 287 int selinux_xfrm_policy_alloc(struct xfrm_sec_ctx **ctxp,
 288                               struct xfrm_user_sec_ctx *uctx,
 289                               gfp_t gfp)
 290 {
 291         return selinux_xfrm_alloc_user(ctxp, uctx, gfp);
 292 }
 293
 294 /*
 295  * LSM hook implementation that copies security data structure from old to new
 296  * for policy cloning.
 297  */
 298 int selinux_xfrm_policy_clone(struct xfrm_sec_ctx *old_ctx,
 299                               struct xfrm_sec_ctx **new_ctxp)
 300 {
 301         struct xfrm_sec_ctx *new_ctx;
 302
 303         if (!old_ctx)
 304                 return 0;
 305
 306         new_ctx = kmemdup(old_ctx, sizeof(*old_ctx) + old_ctx->ctx_len,
 307                           GFP_ATOMIC);
 308         if (!new_ctx)
 309                 return -ENOMEM;
 310         atomic_inc(&selinux_xfrm_refcount);
 311         *new_ctxp = new_ctx;
 312
 313         return 0;
 314 }
 315
 316 /*
 317  * LSM hook implementation that frees xfrm_sec_ctx security information.
 318  */
 319 void selinux_xfrm_policy_free(struct xfrm_sec_ctx *ctx)
 320 {
 321         selinux_xfrm_free(ctx);
 322 }
 323
 324 /*
 325  * LSM hook implementation that authorizes deletion of labeled policies.
 326  */
 327 int selinux_xfrm_policy_delete(struct xfrm_sec_ctx *ctx)
 328 {
 329         return selinux_xfrm_delete(ctx);
 330 }
 331
 332 /*
 333  * LSM hook implementation that allocates a xfrm_sec_state, populates it using
 334  * the supplied security context, and assigns it to the xfrm_state.
 335  */
 336 int selinux_xfrm_state_alloc(struct xfrm_state *x,
 337                              struct xfrm_user_sec_ctx *uctx)
 338 {
 339         return selinux_xfrm_alloc_user(&x->security, uctx, GFP_KERNEL);
 340 }
 341
 342 /*
 343  * LSM hook implementation that allocates a xfrm_sec_state and populates based
 344  * on a secid.
 345  */
 346 int selinux_xfrm_state_alloc_acquire(struct xfrm_state *x,
 347                                      struct xfrm_sec_ctx *polsec, u32 secid)
 348 {
 349         int rc;
 350         struct xfrm_sec_ctx *ctx;
 351         char *ctx_str = NULL;
 352         int str_len;
 353
 354         if (!polsec)
 355                 return 0;
 356
 357         if (secid == 0)
 358                 return -EINVAL;
 359
 360         rc = security_sid_to_context(&selinux_state, secid, &ctx_str,
 361                                      &str_len);
 362         if (rc)
 363                 return rc;
 364
 365         ctx = kmalloc(sizeof(*ctx) + str_len, GFP_ATOMIC);
 366         if (!ctx) {
 367                 rc = -ENOMEM;
 368                 goto out;
 369         }
 370
 371         ctx->ctx_doi = XFRM_SC_DOI_LSM;
 372         ctx->ctx_alg = XFRM_SC_ALG_SELINUX;
 373         ctx->ctx_sid = secid;
 374         ctx->ctx_len = str_len;
 375         memcpy(ctx->ctx_str, ctx_str, str_len);
 376
 377         x->security = ctx;
 378         atomic_inc(&selinux_xfrm_refcount);
 379 out:
 380         kfree(ctx_str);
 381         return rc;
 382 }
 383
 384 /*
 385  * LSM hook implementation that frees xfrm_state security information.
 386  */
 387 void selinux_xfrm_state_free(struct xfrm_state *x)
 388 {
 389         selinux_xfrm_free(x->security);
 390 }
 391
 392 /*
 393  * LSM hook implementation that authorizes deletion of labeled SAs.
 394  */
 395 int selinux_xfrm_state_delete(struct xfrm_state *x)
 396 {
 397         return selinux_xfrm_delete(x->security);
 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 sk_sid, struct sk_buff *skb,
 408                               struct common_audit_data *ad)
 409 {
 410         int i;
 411         struct sec_path *sp = skb_sec_path(skb);
 412         u32 peer_sid = SECINITSID_UNLABELED;
 413
 414         if (sp) {
 415                 for (i = 0; i < sp->len; i++) {
 416                         struct xfrm_state *x = sp->xvec[i];
 417
 418                         if (x && selinux_authorizable_xfrm(x)) {
 419                                 struct xfrm_sec_ctx *ctx = x->security;
 420                                 peer_sid = ctx->ctx_sid;
 421                                 break;
 422                         }
 423                 }
 424         }
 425
 426         /* This check even when there's no association involved is intended,
 427          * according to Trent Jaeger, to make sure a process can't engage in
 428          * non-IPsec communication unless explicitly allowed by policy. */
 429         return avc_has_perm(&selinux_state,
 430                             sk_sid, peer_sid,
 431                             SECCLASS_ASSOCIATION, ASSOCIATION__RECVFROM, ad);
 432 }
 433
 434 /*
 435  * POSTROUTE_LAST hook's XFRM processing:
 436  * If we have no security association, then we need to determine
 437  * whether the socket is allowed to send to an unlabelled destination.
 438  * If we do have a authorizable security association, then it has already been
 439  * checked in the selinux_xfrm_state_pol_flow_match hook above.
 440  */
 441 int selinux_xfrm_postroute_last(u32 sk_sid, struct sk_buff *skb,
 442                                 struct common_audit_data *ad, u8 proto)
 443 {
 444         struct dst_entry *dst;
 445
 446         switch (proto) {
 447         case IPPROTO_AH:
 448         case IPPROTO_ESP:
 449         case IPPROTO_COMP:
 450                 /* We should have already seen this packet once before it
 451                  * underwent xfrm(s). No need to subject it to the unlabeled
 452                  * check. */
 453                 return 0;
 454         default:
 455                 break;
 456         }
 457
 458         dst = skb_dst(skb);
 459         if (dst) {
 460                 struct dst_entry *iter;
 461
 462                 for (iter = dst; iter != NULL; iter = xfrm_dst_child(iter)) {
 463                         struct xfrm_state *x = iter->xfrm;
 464
 465                         if (x && selinux_authorizable_xfrm(x))
 466                                 return 0;
 467                 }
 468         }
 469
 470         /* This check even when there's no association involved is intended,
 471          * according to Trent Jaeger, to make sure a process can't engage in
 472          * non-IPsec communication unless explicitly allowed by policy. */
 473         return avc_has_perm(&selinux_state, sk_sid, SECINITSID_UNLABELED,
 474                             SECCLASS_ASSOCIATION, ASSOCIATION__SENDTO, ad);
 475 }