root/security/selinux/xfrm.c

DEFINITIONS

1. selinux_authorizable_ctx
2. selinux_authorizable_xfrm
3. selinux_xfrm_alloc_user
4. selinux_xfrm_free
5. selinux_xfrm_delete
6. selinux_xfrm_policy_lookup
7. selinux_xfrm_state_pol_flow_match
8. selinux_xfrm_skb_sid_egress
9. selinux_xfrm_skb_sid_ingress
10. selinux_xfrm_decode_session
11. selinux_xfrm_skb_sid
12. selinux_xfrm_policy_alloc
13. selinux_xfrm_policy_clone
14. selinux_xfrm_policy_free
15. selinux_xfrm_policy_delete
16. selinux_xfrm_state_alloc
17. selinux_xfrm_state_alloc_acquire
18. selinux_xfrm_state_free
19. selinux_xfrm_state_delete
20. selinux_xfrm_sock_rcv_skb
21. selinux_xfrm_postroute_last

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  *  NSA Security-Enhanced Linux (SELinux) security module
   4  *
   5  *  This file contains the SELinux XFRM hook function implementations.
   6  *
   7  *  Authors:  Serge Hallyn <sergeh@us.ibm.com>
   8  *            Trent Jaeger <jaegert@us.ibm.com>
   9  *
  10  *  Updated: Venkat Yekkirala <vyekkirala@TrustedCS.com>
  11  *
  12  *           Granular IPSec Associations for use in MLS environments.
  13  *
  14  *  Copyright (C) 2005 International Business Machines Corporation
  15  *  Copyright (C) 2006 Trusted Computer Solutions, Inc.
  16  */
  17 
  18 /*
  19  * USAGE:
  20  * NOTES:
  21  *   1. Make sure to enable the following options in your kernel config:
  22  *      CONFIG_SECURITY=y
  23  *      CONFIG_SECURITY_NETWORK=y
  24  *      CONFIG_SECURITY_NETWORK_XFRM=y
  25  *      CONFIG_SECURITY_SELINUX=m/y
  26  * ISSUES:
  27  *   1. Caching packets, so they are not dropped during negotiation
  28  *   2. Emulating a reasonable SO_PEERSEC across machines
  29  *   3. Testing addition of sk_policy's with security context via setsockopt
  30  */
  31 #include <linux/kernel.h>
  32 #include <linux/init.h>
  33 #include <linux/security.h>
  34 #include <linux/types.h>
  35 #include <linux/slab.h>
  36 #include <linux/ip.h>
  37 #include <linux/tcp.h>
  38 #include <linux/skbuff.h>
  39 #include <linux/xfrm.h>
  40 #include <net/xfrm.h>
  41 #include <net/checksum.h>
  42 #include <net/udp.h>
  43 #include <linux/atomic.h>
  44 
  45 #include "avc.h"
  46 #include "objsec.h"
  47 #include "xfrm.h"
  48 
  49 /* Labeled XFRM instance counter */
  50 atomic_t selinux_xfrm_refcount = ATOMIC_INIT(0);
  51 
  52 /*
  53  * Returns true if the context is an LSM/SELinux context.
  54  */
  55 static inline int selinux_authorizable_ctx(struct xfrm_sec_ctx *ctx)
  56 {
  57         return (ctx &&
  58                 (ctx->ctx_doi == XFRM_SC_DOI_LSM) &&
  59                 (ctx->ctx_alg == XFRM_SC_ALG_SELINUX));
  60 }
  61 
  62 /*
  63  * Returns true if the xfrm contains a security blob for SELinux.
  64  */
  65 static inline int selinux_authorizable_xfrm(struct xfrm_state *x)
  66 {
  67         return selinux_authorizable_ctx(x->security);
  68 }
  69 
  70 /*
  71  * Allocates a xfrm_sec_state and populates it using the supplied security
  72  * xfrm_user_sec_ctx context.
  73  */
  74 static int selinux_xfrm_alloc_user(struct xfrm_sec_ctx **ctxp,
  75                                    struct xfrm_user_sec_ctx *uctx,
  76                                    gfp_t gfp)
  77 {
  78         int rc;
  79         const struct task_security_struct *tsec = selinux_cred(current_cred());
  80         struct xfrm_sec_ctx *ctx = NULL;
  81         u32 str_len;
  82 
  83         if (ctxp == NULL || uctx == NULL ||
  84             uctx->ctx_doi != XFRM_SC_DOI_LSM ||
  85             uctx->ctx_alg != XFRM_SC_ALG_SELINUX)
  86                 return -EINVAL;
  87 
  88         str_len = uctx->ctx_len;
  89         if (str_len >= PAGE_SIZE)
  90                 return -ENOMEM;
  91 
  92         ctx = kmalloc(sizeof(*ctx) + str_len + 1, gfp);
  93         if (!ctx)
  94                 return -ENOMEM;
  95 
  96         ctx->ctx_doi = XFRM_SC_DOI_LSM;
  97         ctx->ctx_alg = XFRM_SC_ALG_SELINUX;
  98         ctx->ctx_len = str_len;
  99         memcpy(ctx->ctx_str, &uctx[1], str_len);
 100         ctx->ctx_str[str_len] = '\0';
 101         rc = security_context_to_sid(&selinux_state, ctx->ctx_str, str_len,
 102                                      &ctx->ctx_sid, gfp);
 103         if (rc)
 104                 goto err;
 105 
 106         rc = avc_has_perm(&selinux_state,
 107                           tsec->sid, ctx->ctx_sid,
 108                           SECCLASS_ASSOCIATION, ASSOCIATION__SETCONTEXT, NULL);
 109         if (rc)
 110                 goto err;
 111 
 112         *ctxp = ctx;
 113         atomic_inc(&selinux_xfrm_refcount);
 114         return 0;
 115 
 116 err:
 117         kfree(ctx);
 118         return rc;
 119 }
 120 
 121 /*
 122  * Free the xfrm_sec_ctx structure.
 123  */
 124 static void selinux_xfrm_free(struct xfrm_sec_ctx *ctx)
 125 {
 126         if (!ctx)
 127                 return;
 128 
 129         atomic_dec(&selinux_xfrm_refcount);
 130         kfree(ctx);
 131 }
 132 
 133 /*
 134  * Authorize the deletion of a labeled SA or policy rule.
 135  */
 136 static int selinux_xfrm_delete(struct xfrm_sec_ctx *ctx)
 137 {
 138         const struct task_security_struct *tsec = selinux_cred(current_cred());
 139 
 140         if (!ctx)
 141                 return 0;
 142 
 143         return avc_has_perm(&selinux_state,
 144                             tsec->sid, ctx->ctx_sid,
 145                             SECCLASS_ASSOCIATION, ASSOCIATION__SETCONTEXT,
 146                             NULL);
 147 }
 148 
 149 /*
 150  * LSM hook implementation that authorizes that a flow can use a xfrm policy
 151  * rule.
 152  */
 153 int selinux_xfrm_policy_lookup(struct xfrm_sec_ctx *ctx, u32 fl_secid, u8 dir)
 154 {
 155         int rc;
 156 
 157         /* All flows should be treated as polmatch'ing an otherwise applicable
 158          * "non-labeled" policy. This would prevent inadvertent "leaks". */
 159         if (!ctx)
 160                 return 0;
 161 
 162         /* Context sid is either set to label or ANY_ASSOC */
 163         if (!selinux_authorizable_ctx(ctx))
 164                 return -EINVAL;
 165 
 166         rc = avc_has_perm(&selinux_state,
 167                           fl_secid, ctx->ctx_sid,
 168                           SECCLASS_ASSOCIATION, ASSOCIATION__POLMATCH, NULL);
 169         return (rc == -EACCES ? -ESRCH : rc);
 170 }
 171 
 172 /*
 173  * LSM hook implementation that authorizes that a state matches
 174  * the given policy, flow combo.
 175  */
 176 int selinux_xfrm_state_pol_flow_match(struct xfrm_state *x,
 177                                       struct xfrm_policy *xp,
 178                                       const struct flowi *fl)
 179 {
 180         u32 state_sid;
 181 
 182         if (!xp->security)
 183                 if (x->security)
 184                         /* unlabeled policy and labeled SA can't match */
 185                         return 0;
 186                 else
 187                         /* unlabeled policy and unlabeled SA match all flows */
 188                         return 1;
 189         else
 190                 if (!x->security)
 191                         /* unlabeled SA and labeled policy can't match */
 192                         return 0;
 193                 else
 194                         if (!selinux_authorizable_xfrm(x))
 195                                 /* Not a SELinux-labeled SA */
 196                                 return 0;
 197 
 198         state_sid = x->security->ctx_sid;
 199 
 200         if (fl->flowi_secid != state_sid)
 201                 return 0;
 202 
 203         /* We don't need a separate SA Vs. policy polmatch check since the SA
 204          * is now of the same label as the flow and a flow Vs. policy polmatch
 205          * check had already happened in selinux_xfrm_policy_lookup() above. */
 206         return (avc_has_perm(&selinux_state,
 207                              fl->flowi_secid, state_sid,
 208                             SECCLASS_ASSOCIATION, ASSOCIATION__SENDTO,
 209                             NULL) ? 0 : 1);
 210 }
 211 
 212 static u32 selinux_xfrm_skb_sid_egress(struct sk_buff *skb)
 213 {
 214         struct dst_entry *dst = skb_dst(skb);
 215         struct xfrm_state *x;
 216 
 217         if (dst == NULL)
 218                 return SECSID_NULL;
 219         x = dst->xfrm;
 220         if (x == NULL || !selinux_authorizable_xfrm(x))
 221                 return SECSID_NULL;
 222 
 223         return x->security->ctx_sid;
 224 }
 225 
 226 static int selinux_xfrm_skb_sid_ingress(struct sk_buff *skb,
 227                                         u32 *sid, int ckall)
 228 {
 229         u32 sid_session = SECSID_NULL;
 230         struct sec_path *sp = skb_sec_path(skb);
 231 
 232         if (sp) {
 233                 int i;
 234 
 235                 for (i = sp->len - 1; i >= 0; i--) {
 236                         struct xfrm_state *x = sp->xvec[i];
 237                         if (selinux_authorizable_xfrm(x)) {
 238                                 struct xfrm_sec_ctx *ctx = x->security;
 239 
 240                                 if (sid_session == SECSID_NULL) {
 241                                         sid_session = ctx->ctx_sid;
 242                                         if (!ckall)
 243                                                 goto out;
 244                                 } else if (sid_session != ctx->ctx_sid) {
 245                                         *sid = SECSID_NULL;
 246                                         return -EINVAL;
 247                                 }
 248                         }
 249                 }
 250         }
 251 
 252 out:
 253         *sid = sid_session;
 254         return 0;
 255 }
 256 
 257 /*
 258  * LSM hook implementation that checks and/or returns the xfrm sid for the
 259  * incoming packet.
 260  */
 261 int selinux_xfrm_decode_session(struct sk_buff *skb, u32 *sid, int ckall)
 262 {
 263         if (skb == NULL) {
 264                 *sid = SECSID_NULL;
 265                 return 0;
 266         }
 267         return selinux_xfrm_skb_sid_ingress(skb, sid, ckall);
 268 }
 269 
 270 int selinux_xfrm_skb_sid(struct sk_buff *skb, u32 *sid)
 271 {
 272         int rc;
 273 
 274         rc = selinux_xfrm_skb_sid_ingress(skb, sid, 0);
 275         if (rc == 0 && *sid == SECSID_NULL)
 276                 *sid = selinux_xfrm_skb_sid_egress(skb);
 277 
 278         return rc;
 279 }
 280 
 281 /*
 282  * LSM hook implementation that allocs and transfers uctx spec to xfrm_policy.
 283  */
 284 int selinux_xfrm_policy_alloc(struct xfrm_sec_ctx **ctxp,
 285                               struct xfrm_user_sec_ctx *uctx,
 286                               gfp_t gfp)
 287 {
 288         return selinux_xfrm_alloc_user(ctxp, uctx, gfp);
 289 }
 290 
 291 /*
 292  * LSM hook implementation that copies security data structure from old to new
 293  * for policy cloning.
 294  */
 295 int selinux_xfrm_policy_clone(struct xfrm_sec_ctx *old_ctx,
 296                               struct xfrm_sec_ctx **new_ctxp)
 297 {
 298         struct xfrm_sec_ctx *new_ctx;
 299 
 300         if (!old_ctx)
 301                 return 0;
 302 
 303         new_ctx = kmemdup(old_ctx, sizeof(*old_ctx) + old_ctx->ctx_len,
 304                           GFP_ATOMIC);
 305         if (!new_ctx)
 306                 return -ENOMEM;
 307         atomic_inc(&selinux_xfrm_refcount);
 308         *new_ctxp = new_ctx;
 309 
 310         return 0;
 311 }
 312 
 313 /*
 314  * LSM hook implementation that frees xfrm_sec_ctx security information.
 315  */
 316 void selinux_xfrm_policy_free(struct xfrm_sec_ctx *ctx)
 317 {
 318         selinux_xfrm_free(ctx);
 319 }
 320 
 321 /*
 322  * LSM hook implementation that authorizes deletion of labeled policies.
 323  */
 324 int selinux_xfrm_policy_delete(struct xfrm_sec_ctx *ctx)
 325 {
 326         return selinux_xfrm_delete(ctx);
 327 }
 328 
 329 /*
 330  * LSM hook implementation that allocates a xfrm_sec_state, populates it using
 331  * the supplied security context, and assigns it to the xfrm_state.
 332  */
 333 int selinux_xfrm_state_alloc(struct xfrm_state *x,
 334                              struct xfrm_user_sec_ctx *uctx)
 335 {
 336         return selinux_xfrm_alloc_user(&x->security, uctx, GFP_KERNEL);
 337 }
 338 
 339 /*
 340  * LSM hook implementation that allocates a xfrm_sec_state and populates based
 341  * on a secid.
 342  */
 343 int selinux_xfrm_state_alloc_acquire(struct xfrm_state *x,
 344                                      struct xfrm_sec_ctx *polsec, u32 secid)
 345 {
 346         int rc;
 347         struct xfrm_sec_ctx *ctx;
 348         char *ctx_str = NULL;
 349         int str_len;
 350 
 351         if (!polsec)
 352                 return 0;
 353 
 354         if (secid == 0)
 355                 return -EINVAL;
 356 
 357         rc = security_sid_to_context(&selinux_state, secid, &ctx_str,
 358                                      &str_len);
 359         if (rc)
 360                 return rc;
 361 
 362         ctx = kmalloc(sizeof(*ctx) + str_len, GFP_ATOMIC);
 363         if (!ctx) {
 364                 rc = -ENOMEM;
 365                 goto out;
 366         }
 367 
 368         ctx->ctx_doi = XFRM_SC_DOI_LSM;
 369         ctx->ctx_alg = XFRM_SC_ALG_SELINUX;
 370         ctx->ctx_sid = secid;
 371         ctx->ctx_len = str_len;
 372         memcpy(ctx->ctx_str, ctx_str, str_len);
 373 
 374         x->security = ctx;
 375         atomic_inc(&selinux_xfrm_refcount);
 376 out:
 377         kfree(ctx_str);
 378         return rc;
 379 }
 380 
 381 /*
 382  * LSM hook implementation that frees xfrm_state security information.
 383  */
 384 void selinux_xfrm_state_free(struct xfrm_state *x)
 385 {
 386         selinux_xfrm_free(x->security);
 387 }
 388 
 389 /*
 390  * LSM hook implementation that authorizes deletion of labeled SAs.
 391  */
 392 int selinux_xfrm_state_delete(struct xfrm_state *x)
 393 {
 394         return selinux_xfrm_delete(x->security);
 395 }
 396 
 397 /*
 398  * LSM hook that controls access to unlabelled packets.  If
 399  * a xfrm_state is authorizable (defined by macro) then it was
 400  * already authorized by the IPSec process.  If not, then
 401  * we need to check for unlabelled access since this may not have
 402  * gone thru the IPSec process.
 403  */
 404 int selinux_xfrm_sock_rcv_skb(u32 sk_sid, struct sk_buff *skb,
 405                               struct common_audit_data *ad)
 406 {
 407         int i;
 408         struct sec_path *sp = skb_sec_path(skb);
 409         u32 peer_sid = SECINITSID_UNLABELED;
 410 
 411         if (sp) {
 412                 for (i = 0; i < sp->len; i++) {
 413                         struct xfrm_state *x = sp->xvec[i];
 414 
 415                         if (x && selinux_authorizable_xfrm(x)) {
 416                                 struct xfrm_sec_ctx *ctx = x->security;
 417                                 peer_sid = ctx->ctx_sid;
 418                                 break;
 419                         }
 420                 }
 421         }
 422 
 423         /* This check even when there's no association involved is intended,
 424          * according to Trent Jaeger, to make sure a process can't engage in
 425          * non-IPsec communication unless explicitly allowed by policy. */
 426         return avc_has_perm(&selinux_state,
 427                             sk_sid, peer_sid,
 428                             SECCLASS_ASSOCIATION, ASSOCIATION__RECVFROM, ad);
 429 }
 430 
 431 /*
 432  * POSTROUTE_LAST hook's XFRM processing:
 433  * If we have no security association, then we need to determine
 434  * whether the socket is allowed to send to an unlabelled destination.
 435  * If we do have a authorizable security association, then it has already been
 436  * checked in the selinux_xfrm_state_pol_flow_match hook above.
 437  */
 438 int selinux_xfrm_postroute_last(u32 sk_sid, struct sk_buff *skb,
 439                                 struct common_audit_data *ad, u8 proto)
 440 {
 441         struct dst_entry *dst;
 442 
 443         switch (proto) {
 444         case IPPROTO_AH:
 445         case IPPROTO_ESP:
 446         case IPPROTO_COMP:
 447                 /* We should have already seen this packet once before it
 448                  * underwent xfrm(s). No need to subject it to the unlabeled
 449                  * check. */
 450                 return 0;
 451         default:
 452                 break;
 453         }
 454 
 455         dst = skb_dst(skb);
 456         if (dst) {
 457                 struct dst_entry *iter;
 458 
 459                 for (iter = dst; iter != NULL; iter = xfrm_dst_child(iter)) {
 460                         struct xfrm_state *x = iter->xfrm;
 461 
 462                         if (x && selinux_authorizable_xfrm(x))
 463                                 return 0;
 464                 }
 465         }
 466 
 467         /* This check even when there's no association involved is intended,
 468          * according to Trent Jaeger, to make sure a process can't engage in
 469          * non-IPsec communication unless explicitly allowed by policy. */
 470         return avc_has_perm(&selinux_state, sk_sid, SECINITSID_UNLABELED,
 471                             SECCLASS_ASSOCIATION, ASSOCIATION__SENDTO, ad);
 472 }