security/selinux/xfrm.c

   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 __read_mostly = 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)
 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_common *flic)
 179 {
 180         u32 state_sid;
 181         u32 flic_sid;
 182
 183         if (!xp->security)
 184                 if (x->security)
 185                         /* unlabeled policy and labeled SA can't match */
 186                         return 0;
 187                 else
 188                         /* unlabeled policy and unlabeled SA match all flows */
 189                         return 1;
 190         else
 191                 if (!x->security)
 192                         /* unlabeled SA and labeled policy can't match */
 193                         return 0;
 194                 else
 195                         if (!selinux_authorizable_xfrm(x))
 196                                 /* Not a SELinux-labeled SA */
 197                                 return 0;
 198
 199         state_sid = x->security->ctx_sid;
 200         flic_sid = flic->flowic_secid;
 201
 202         if (flic_sid != state_sid)
 203                 return 0;
 204
 205         /* We don't need a separate SA Vs. policy polmatch check since the SA
 206          * is now of the same label as the flow and a flow Vs. policy polmatch
 207          * check had already happened in selinux_xfrm_policy_lookup() above. */
 208         return (avc_has_perm(&selinux_state, flic_sid, state_sid,
 209                              SECCLASS_ASSOCIATION, ASSOCIATION__SENDTO,
 210                              NULL) ? 0 : 1);
 211 }
 212
 213 static u32 selinux_xfrm_skb_sid_egress(struct sk_buff *skb)
 214 {
 215         struct dst_entry *dst = skb_dst(skb);
 216         struct xfrm_state *x;
 217
 218         if (dst == NULL)
 219                 return SECSID_NULL;
 220         x = dst->xfrm;
 221         if (x == NULL || !selinux_authorizable_xfrm(x))
 222                 return SECSID_NULL;
 223
 224         return x->security->ctx_sid;
 225 }
 226
 227 static int selinux_xfrm_skb_sid_ingress(struct sk_buff *skb,
 228                                         u32 *sid, int ckall)
 229 {
 230         u32 sid_session = SECSID_NULL;
 231         struct sec_path *sp = skb_sec_path(skb);
 232
 233         if (sp) {
 234                 int i;
 235
 236                 for (i = sp->len - 1; i >= 0; i--) {
 237                         struct xfrm_state *x = sp->xvec[i];
 238                         if (selinux_authorizable_xfrm(x)) {
 239                                 struct xfrm_sec_ctx *ctx = x->security;
 240
 241                                 if (sid_session == SECSID_NULL) {
 242                                         sid_session = ctx->ctx_sid;
 243                                         if (!ckall)
 244                                                 goto out;
 245                                 } else if (sid_session != ctx->ctx_sid) {
 246                                         *sid = SECSID_NULL;
 247                                         return -EINVAL;
 248                                 }
 249                         }
 250                 }
 251         }
 252
 253 out:
 254         *sid = sid_session;
 255         return 0;
 256 }
 257
 258 /*
 259  * LSM hook implementation that checks and/or returns the xfrm sid for the
 260  * incoming packet.
 261  */
 262 int selinux_xfrm_decode_session(struct sk_buff *skb, u32 *sid, int ckall)
 263 {
 264         if (skb == NULL) {
 265                 *sid = SECSID_NULL;
 266                 return 0;
 267         }
 268         return selinux_xfrm_skb_sid_ingress(skb, sid, ckall);
 269 }
 270
 271 int selinux_xfrm_skb_sid(struct sk_buff *skb, u32 *sid)
 272 {
 273         int rc;
 274
 275         rc = selinux_xfrm_skb_sid_ingress(skb, sid, 0);
 276         if (rc == 0 && *sid == SECSID_NULL)
 277                 *sid = selinux_xfrm_skb_sid_egress(skb);
 278
 279         return rc;
 280 }
 281
 282 /*
 283  * LSM hook implementation that allocs and transfers uctx spec to xfrm_policy.
 284  */
 285 int selinux_xfrm_policy_alloc(struct xfrm_sec_ctx **ctxp,
 286                               struct xfrm_user_sec_ctx *uctx,
 287                               gfp_t gfp)
 288 {
 289         return selinux_xfrm_alloc_user(ctxp, uctx, gfp);
 290 }
 291
 292 /*
 293  * LSM hook implementation that copies security data structure from old to new
 294  * for policy cloning.
 295  */
 296 int selinux_xfrm_policy_clone(struct xfrm_sec_ctx *old_ctx,
 297                               struct xfrm_sec_ctx **new_ctxp)
 298 {
 299         struct xfrm_sec_ctx *new_ctx;
 300
 301         if (!old_ctx)
 302                 return 0;
 303
 304         new_ctx = kmemdup(old_ctx, sizeof(*old_ctx) + old_ctx->ctx_len,
 305                           GFP_ATOMIC);
 306         if (!new_ctx)
 307                 return -ENOMEM;
 308         atomic_inc(&selinux_xfrm_refcount);
 309         *new_ctxp = new_ctx;
 310
 311         return 0;
 312 }
 313
 314 /*
 315  * LSM hook implementation that frees xfrm_sec_ctx security information.
 316  */
 317 void selinux_xfrm_policy_free(struct xfrm_sec_ctx *ctx)
 318 {
 319         selinux_xfrm_free(ctx);
 320 }
 321
 322 /*
 323  * LSM hook implementation that authorizes deletion of labeled policies.
 324  */
 325 int selinux_xfrm_policy_delete(struct xfrm_sec_ctx *ctx)
 326 {
 327         return selinux_xfrm_delete(ctx);
 328 }
 329
 330 /*
 331  * LSM hook implementation that allocates a xfrm_sec_state, populates it using
 332  * the supplied security context, and assigns it to the xfrm_state.
 333  */
 334 int selinux_xfrm_state_alloc(struct xfrm_state *x,
 335                              struct xfrm_user_sec_ctx *uctx)
 336 {
 337         return selinux_xfrm_alloc_user(&x->security, uctx, GFP_KERNEL);
 338 }
 339
 340 /*
 341  * LSM hook implementation that allocates a xfrm_sec_state and populates based
 342  * on a secid.
 343  */
 344 int selinux_xfrm_state_alloc_acquire(struct xfrm_state *x,
 345                                      struct xfrm_sec_ctx *polsec, u32 secid)
 346 {
 347         int rc;
 348         struct xfrm_sec_ctx *ctx;
 349         char *ctx_str = NULL;
 350         u32 str_len;
 351
 352         if (!polsec)
 353                 return 0;
 354
 355         if (secid == 0)
 356                 return -EINVAL;
 357
 358         rc = security_sid_to_context(&selinux_state, secid, &ctx_str,
 359                                      &str_len);
 360         if (rc)
 361                 return rc;
 362
 363         ctx = kmalloc(sizeof(*ctx) + str_len, GFP_ATOMIC);
 364         if (!ctx) {
 365                 rc = -ENOMEM;
 366                 goto out;
 367         }
 368
 369         ctx->ctx_doi = XFRM_SC_DOI_LSM;
 370         ctx->ctx_alg = XFRM_SC_ALG_SELINUX;
 371         ctx->ctx_sid = secid;
 372         ctx->ctx_len = str_len;
 373         memcpy(ctx->ctx_str, ctx_str, str_len);
 374
 375         x->security = ctx;
 376         atomic_inc(&selinux_xfrm_refcount);
 377 out:
 378         kfree(ctx_str);
 379         return rc;
 380 }
 381
 382 /*
 383  * LSM hook implementation that frees xfrm_state security information.
 384  */
 385 void selinux_xfrm_state_free(struct xfrm_state *x)
 386 {
 387         selinux_xfrm_free(x->security);
 388 }
 389
 390 /*
 391  * LSM hook implementation that authorizes deletion of labeled SAs.
 392  */
 393 int selinux_xfrm_state_delete(struct xfrm_state *x)
 394 {
 395         return selinux_xfrm_delete(x->security);
 396 }
 397
 398 /*
 399  * LSM hook that controls access to unlabelled packets.  If
 400  * a xfrm_state is authorizable (defined by macro) then it was
 401  * already authorized by the IPSec process.  If not, then
 402  * we need to check for unlabelled access since this may not have
 403  * gone thru the IPSec process.
 404  */
 405 int selinux_xfrm_sock_rcv_skb(u32 sk_sid, struct sk_buff *skb,
 406                               struct common_audit_data *ad)
 407 {
 408         int i;
 409         struct sec_path *sp = skb_sec_path(skb);
 410         u32 peer_sid = SECINITSID_UNLABELED;
 411
 412         if (sp) {
 413                 for (i = 0; i < sp->len; i++) {
 414                         struct xfrm_state *x = sp->xvec[i];
 415
 416                         if (x && selinux_authorizable_xfrm(x)) {
 417                                 struct xfrm_sec_ctx *ctx = x->security;
 418                                 peer_sid = ctx->ctx_sid;
 419                                 break;
 420                         }
 421                 }
 422         }
 423
 424         /* This check even when there's no association involved is intended,
 425          * according to Trent Jaeger, to make sure a process can't engage in
 426          * non-IPsec communication unless explicitly allowed by policy. */
 427         return avc_has_perm(&selinux_state,
 428                             sk_sid, peer_sid,
 429                             SECCLASS_ASSOCIATION, ASSOCIATION__RECVFROM, ad);
 430 }
 431
 432 /*
 433  * POSTROUTE_LAST hook's XFRM processing:
 434  * If we have no security association, then we need to determine
 435  * whether the socket is allowed to send to an unlabelled destination.
 436  * If we do have a authorizable security association, then it has already been
 437  * checked in the selinux_xfrm_state_pol_flow_match hook above.
 438  */
 439 int selinux_xfrm_postroute_last(u32 sk_sid, struct sk_buff *skb,
 440                                 struct common_audit_data *ad, u8 proto)
 441 {
 442         struct dst_entry *dst;
 443
 444         switch (proto) {
 445         case IPPROTO_AH:
 446         case IPPROTO_ESP:
 447         case IPPROTO_COMP:
 448                 /* We should have already seen this packet once before it
 449                  * underwent xfrm(s). No need to subject it to the unlabeled
 450                  * check. */
 451                 return 0;
 452         default:
 453                 break;
 454         }
 455
 456         dst = skb_dst(skb);
 457         if (dst) {
 458                 struct dst_entry *iter;
 459
 460                 for (iter = dst; iter != NULL; iter = xfrm_dst_child(iter)) {
 461                         struct xfrm_state *x = iter->xfrm;
 462
 463                         if (x && selinux_authorizable_xfrm(x))
 464                                 return 0;
 465                 }
 466         }
 467
 468         /* This check even when there's no association involved is intended,
 469          * according to Trent Jaeger, to make sure a process can't engage in
 470          * non-IPsec communication unless explicitly allowed by policy. */
 471         return avc_has_perm(&selinux_state, sk_sid, SECINITSID_UNLABELED,
 472                             SECCLASS_ASSOCIATION, ASSOCIATION__SENDTO, ad);
 473 }