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 = current_security();
  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(ctx->ctx_str, str_len, &ctx->ctx_sid, gfp);
 105         if (rc)
 106                 goto err;
 107
 108         rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
 109                           SECCLASS_ASSOCIATION, ASSOCIATION__SETCONTEXT, NULL);
 110         if (rc)
 111                 goto err;
 112
 113         *ctxp = ctx;
 114         atomic_inc(&selinux_xfrm_refcount);
 115         return 0;
 116
 117 err:
 118         kfree(ctx);
 119         return rc;
 120 }
 121
 122 /*
 123  * Free the xfrm_sec_ctx structure.
 124  */
 125 static void selinux_xfrm_free(struct xfrm_sec_ctx *ctx)
 126 {
 127         if (!ctx)
 128                 return;
 129
 130         atomic_dec(&selinux_xfrm_refcount);
 131         kfree(ctx);
 132 }
 133
 134 /*
 135  * Authorize the deletion of a labeled SA or policy rule.
 136  */
 137 static int selinux_xfrm_delete(struct xfrm_sec_ctx *ctx)
 138 {
 139         const struct task_security_struct *tsec = current_security();
 140
 141         if (!ctx)
 142                 return 0;
 143
 144         return avc_has_perm(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(fl_secid, ctx->ctx_sid,
 167                           SECCLASS_ASSOCIATION, ASSOCIATION__POLMATCH, NULL);
 168         return (rc == -EACCES ? -ESRCH : rc);
 169 }
 170
 171 /*
 172  * LSM hook implementation that authorizes that a state matches
 173  * the given policy, flow combo.
 174  */
 175 int selinux_xfrm_state_pol_flow_match(struct xfrm_state *x,
 176                                       struct xfrm_policy *xp,
 177                                       const struct flowi *fl)
 178 {
 179         u32 state_sid;
 180
 181         if (!xp->security)
 182                 if (x->security)
 183                         /* unlabeled policy and labeled SA can't match */
 184                         return 0;
 185                 else
 186                         /* unlabeled policy and unlabeled SA match all flows */
 187                         return 1;
 188         else
 189                 if (!x->security)
 190                         /* unlabeled SA and labeled policy can't match */
 191                         return 0;
 192                 else
 193                         if (!selinux_authorizable_xfrm(x))
 194                                 /* Not a SELinux-labeled SA */
 195                                 return 0;
 196
 197         state_sid = x->security->ctx_sid;
 198
 199         if (fl->flowi_secid != state_sid)
 200                 return 0;
 201
 202         /* We don't need a separate SA Vs. policy polmatch check since the SA
 203          * is now of the same label as the flow and a flow Vs. policy polmatch
 204          * check had already happened in selinux_xfrm_policy_lookup() above. */
 205         return (avc_has_perm(fl->flowi_secid, state_sid,
 206                             SECCLASS_ASSOCIATION, ASSOCIATION__SENDTO,
 207                             NULL) ? 0 : 1);
 208 }
 209
 210 static u32 selinux_xfrm_skb_sid_egress(struct sk_buff *skb)
 211 {
 212         struct dst_entry *dst = skb_dst(skb);
 213         struct xfrm_state *x;
 214
 215         if (dst == NULL)
 216                 return SECSID_NULL;
 217         x = dst->xfrm;
 218         if (x == NULL || !selinux_authorizable_xfrm(x))
 219                 return SECSID_NULL;
 220
 221         return x->security->ctx_sid;
 222 }
 223
 224 static int selinux_xfrm_skb_sid_ingress(struct sk_buff *skb,
 225                                         u32 *sid, int ckall)
 226 {
 227         u32 sid_session = SECSID_NULL;
 228         struct sec_path *sp = skb->sp;
 229
 230         if (sp) {
 231                 int i;
 232
 233                 for (i = sp->len - 1; i >= 0; i--) {
 234                         struct xfrm_state *x = sp->xvec[i];
 235                         if (selinux_authorizable_xfrm(x)) {
 236                                 struct xfrm_sec_ctx *ctx = x->security;
 237
 238                                 if (sid_session == SECSID_NULL) {
 239                                         sid_session = ctx->ctx_sid;
 240                                         if (!ckall)
 241                                                 goto out;
 242                                 } else if (sid_session != ctx->ctx_sid) {
 243                                         *sid = SECSID_NULL;
 244                                         return -EINVAL;
 245                                 }
 246                         }
 247                 }
 248         }
 249
 250 out:
 251         *sid = sid_session;
 252         return 0;
 253 }
 254
 255 /*
 256  * LSM hook implementation that checks and/or returns the xfrm sid for the
 257  * incoming packet.
 258  */
 259 int selinux_xfrm_decode_session(struct sk_buff *skb, u32 *sid, int ckall)
 260 {
 261         if (skb == NULL) {
 262                 *sid = SECSID_NULL;
 263                 return 0;
 264         }
 265         return selinux_xfrm_skb_sid_ingress(skb, sid, ckall);
 266 }
 267
 268 int selinux_xfrm_skb_sid(struct sk_buff *skb, u32 *sid)
 269 {
 270         int rc;
 271
 272         rc = selinux_xfrm_skb_sid_ingress(skb, sid, 0);
 273         if (rc == 0 && *sid == SECSID_NULL)
 274                 *sid = selinux_xfrm_skb_sid_egress(skb);
 275
 276         return rc;
 277 }
 278
 279 /*
 280  * LSM hook implementation that allocs and transfers uctx spec to xfrm_policy.
 281  */
 282 int selinux_xfrm_policy_alloc(struct xfrm_sec_ctx **ctxp,
 283                               struct xfrm_user_sec_ctx *uctx,
 284                               gfp_t gfp)
 285 {
 286         return selinux_xfrm_alloc_user(ctxp, uctx, gfp);
 287 }
 288
 289 /*
 290  * LSM hook implementation that copies security data structure from old to new
 291  * for policy cloning.
 292  */
 293 int selinux_xfrm_policy_clone(struct xfrm_sec_ctx *old_ctx,
 294                               struct xfrm_sec_ctx **new_ctxp)
 295 {
 296         struct xfrm_sec_ctx *new_ctx;
 297
 298         if (!old_ctx)
 299                 return 0;
 300
 301         new_ctx = kmemdup(old_ctx, sizeof(*old_ctx) + old_ctx->ctx_len,
 302                           GFP_ATOMIC);
 303         if (!new_ctx)
 304                 return -ENOMEM;
 305         atomic_inc(&selinux_xfrm_refcount);
 306         *new_ctxp = new_ctx;
 307
 308         return 0;
 309 }
 310
 311 /*
 312  * LSM hook implementation that frees xfrm_sec_ctx security information.
 313  */
 314 void selinux_xfrm_policy_free(struct xfrm_sec_ctx *ctx)
 315 {
 316         selinux_xfrm_free(ctx);
 317 }
 318
 319 /*
 320  * LSM hook implementation that authorizes deletion of labeled policies.
 321  */
 322 int selinux_xfrm_policy_delete(struct xfrm_sec_ctx *ctx)
 323 {
 324         return selinux_xfrm_delete(ctx);
 325 }
 326
 327 /*
 328  * LSM hook implementation that allocates a xfrm_sec_state, populates it using
 329  * the supplied security context, and assigns it to the xfrm_state.
 330  */
 331 int selinux_xfrm_state_alloc(struct xfrm_state *x,
 332                              struct xfrm_user_sec_ctx *uctx)
 333 {
 334         return selinux_xfrm_alloc_user(&x->security, uctx, GFP_KERNEL);
 335 }
 336
 337 /*
 338  * LSM hook implementation that allocates a xfrm_sec_state and populates based
 339  * on a secid.
 340  */
 341 int selinux_xfrm_state_alloc_acquire(struct xfrm_state *x,
 342                                      struct xfrm_sec_ctx *polsec, u32 secid)
 343 {
 344         int rc;
 345         struct xfrm_sec_ctx *ctx;
 346         char *ctx_str = NULL;
 347         int str_len;
 348
 349         if (!polsec)
 350                 return 0;
 351
 352         if (secid == 0)
 353                 return -EINVAL;
 354
 355         rc = security_sid_to_context(secid, &ctx_str, &str_len);
 356         if (rc)
 357                 return rc;
 358
 359         ctx = kmalloc(sizeof(*ctx) + str_len, GFP_ATOMIC);
 360         if (!ctx) {
 361                 rc = -ENOMEM;
 362                 goto out;
 363         }
 364
 365         ctx->ctx_doi = XFRM_SC_DOI_LSM;
 366         ctx->ctx_alg = XFRM_SC_ALG_SELINUX;
 367         ctx->ctx_sid = secid;
 368         ctx->ctx_len = str_len;
 369         memcpy(ctx->ctx_str, ctx_str, str_len);
 370
 371         x->security = ctx;
 372         atomic_inc(&selinux_xfrm_refcount);
 373 out:
 374         kfree(ctx_str);
 375         return rc;
 376 }
 377
 378 /*
 379  * LSM hook implementation that frees xfrm_state security information.
 380  */
 381 void selinux_xfrm_state_free(struct xfrm_state *x)
 382 {
 383         selinux_xfrm_free(x->security);
 384 }
 385
 386 /*
 387  * LSM hook implementation that authorizes deletion of labeled SAs.
 388  */
 389 int selinux_xfrm_state_delete(struct xfrm_state *x)
 390 {
 391         return selinux_xfrm_delete(x->security);
 392 }
 393
 394 /*
 395  * LSM hook that controls access to unlabelled packets.  If
 396  * a xfrm_state is authorizable (defined by macro) then it was
 397  * already authorized by the IPSec process.  If not, then
 398  * we need to check for unlabelled access since this may not have
 399  * gone thru the IPSec process.
 400  */
 401 int selinux_xfrm_sock_rcv_skb(u32 sk_sid, struct sk_buff *skb,
 402                               struct common_audit_data *ad)
 403 {
 404         int i;
 405         struct sec_path *sp = skb->sp;
 406         u32 peer_sid = SECINITSID_UNLABELED;
 407
 408         if (sp) {
 409                 for (i = 0; i < sp->len; i++) {
 410                         struct xfrm_state *x = sp->xvec[i];
 411
 412                         if (x && selinux_authorizable_xfrm(x)) {
 413                                 struct xfrm_sec_ctx *ctx = x->security;
 414                                 peer_sid = ctx->ctx_sid;
 415                                 break;
 416                         }
 417                 }
 418         }
 419
 420         /* This check even when there's no association involved is intended,
 421          * according to Trent Jaeger, to make sure a process can't engage in
 422          * non-IPsec communication unless explicitly allowed by policy. */
 423         return avc_has_perm(sk_sid, peer_sid,
 424                             SECCLASS_ASSOCIATION, ASSOCIATION__RECVFROM, ad);
 425 }
 426
 427 /*
 428  * POSTROUTE_LAST hook's XFRM processing:
 429  * If we have no security association, then we need to determine
 430  * whether the socket is allowed to send to an unlabelled destination.
 431  * If we do have a authorizable security association, then it has already been
 432  * checked in the selinux_xfrm_state_pol_flow_match hook above.
 433  */
 434 int selinux_xfrm_postroute_last(u32 sk_sid, struct sk_buff *skb,
 435                                 struct common_audit_data *ad, u8 proto)
 436 {
 437         struct dst_entry *dst;
 438
 439         switch (proto) {
 440         case IPPROTO_AH:
 441         case IPPROTO_ESP:
 442         case IPPROTO_COMP:
 443                 /* We should have already seen this packet once before it
 444                  * underwent xfrm(s). No need to subject it to the unlabeled
 445                  * check. */
 446                 return 0;
 447         default:
 448                 break;
 449         }
 450
 451         dst = skb_dst(skb);
 452         if (dst) {
 453                 struct dst_entry *iter;
 454
 455                 for (iter = dst; iter != NULL; iter = iter->child) {
 456                         struct xfrm_state *x = iter->xfrm;
 457
 458                         if (x && selinux_authorizable_xfrm(x))
 459                                 return 0;
 460                 }
 461         }
 462
 463         /* This check even when there's no association involved is intended,
 464          * according to Trent Jaeger, to make sure a process can't engage in
 465          * non-IPsec communication unless explicitly allowed by policy. */
 466         return avc_has_perm(sk_sid, SECINITSID_UNLABELED,
 467                             SECCLASS_ASSOCIATION, ASSOCIATION__SENDTO, ad);
 468 }