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/slab.h>
  42 #include <linux/ip.h>
  43 #include <linux/tcp.h>
  44 #include <linux/skbuff.h>
  45 #include <linux/xfrm.h>
  46 #include <net/xfrm.h>
  47 #include <net/checksum.h>
  48 #include <net/udp.h>
  49 #include <linux/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 the context is 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  * Allocates a xfrm_sec_state and populates it using the supplied security
  78  * xfrm_user_sec_ctx context.
  79  */
  80 static int selinux_xfrm_alloc_user(struct xfrm_sec_ctx **ctxp,
  81                                    struct xfrm_user_sec_ctx *uctx)
  82 {
  83         int rc;
  84         const struct task_security_struct *tsec = current_security();
  85         struct xfrm_sec_ctx *ctx = NULL;
  86         u32 str_len;
  87
  88         if (ctxp == NULL || uctx == NULL ||
  89             uctx->ctx_doi != XFRM_SC_DOI_LSM ||
  90             uctx->ctx_alg != XFRM_SC_ALG_SELINUX)
  91                 return -EINVAL;
  92
  93         str_len = uctx->ctx_len;
  94         if (str_len >= PAGE_SIZE)
  95                 return -ENOMEM;
  96
  97         ctx = kmalloc(sizeof(*ctx) + str_len + 1, GFP_KERNEL);
  98         if (!ctx)
  99                 return -ENOMEM;
 100
 101         ctx->ctx_doi = XFRM_SC_DOI_LSM;
 102         ctx->ctx_alg = XFRM_SC_ALG_SELINUX;
 103         ctx->ctx_len = str_len;
 104         memcpy(ctx->ctx_str, &uctx[1], str_len);
 105         ctx->ctx_str[str_len] = '\0';
 106         rc = security_context_to_sid(ctx->ctx_str, str_len, &ctx->ctx_sid);
 107         if (rc)
 108                 goto err;
 109
 110         rc = avc_has_perm(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 = current_security();
 142
 143         if (!ctx)
 144                 return 0;
 145
 146         return avc_has_perm(tsec->sid, ctx->ctx_sid,
 147                             SECCLASS_ASSOCIATION, ASSOCIATION__SETCONTEXT,
 148                             NULL);
 149 }
 150
 151 /*
 152  * LSM hook implementation that authorizes that a flow can use a xfrm policy
 153  * rule.
 154  */
 155 int selinux_xfrm_policy_lookup(struct xfrm_sec_ctx *ctx, u32 fl_secid, u8 dir)
 156 {
 157         int rc;
 158
 159         /* All flows should be treated as polmatch'ing an otherwise applicable
 160          * "non-labeled" policy. This would prevent inadvertent "leaks". */
 161         if (!ctx)
 162                 return 0;
 163
 164         /* Context sid is either set to label or ANY_ASSOC */
 165         if (!selinux_authorizable_ctx(ctx))
 166                 return -EINVAL;
 167
 168         rc = avc_has_perm(fl_secid, ctx->ctx_sid,
 169                           SECCLASS_ASSOCIATION, ASSOCIATION__POLMATCH, NULL);
 170         return (rc == -EACCES ? -ESRCH : rc);
 171 }
 172
 173 /*
 174  * LSM hook implementation that authorizes that a state matches
 175  * the given policy, flow combo.
 176  */
 177 int selinux_xfrm_state_pol_flow_match(struct xfrm_state *x,
 178                                       struct xfrm_policy *xp,
 179                                       const struct flowi *fl)
 180 {
 181         u32 state_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
 201         if (fl->flowi_secid != state_sid)
 202                 return 0;
 203
 204         /* We don't need a separate SA Vs. policy polmatch check since the SA
 205          * is now of the same label as the flow and a flow Vs. policy polmatch
 206          * check had already happened in selinux_xfrm_policy_lookup() above. */
 207         return (avc_has_perm(fl->flowi_secid, state_sid,
 208                             SECCLASS_ASSOCIATION, ASSOCIATION__SENDTO,
 209                             NULL) ? 0 : 1);
 210 }
 211
 212 /*
 213  * LSM hook implementation that checks and/or returns the xfrm sid for the
 214  * incoming packet.
 215  */
 216 int selinux_xfrm_decode_session(struct sk_buff *skb, u32 *sid, int ckall)
 217 {
 218         u32 sid_session = SECSID_NULL;
 219         struct sec_path *sp;
 220
 221         if (skb == NULL)
 222                 goto out;
 223
 224         sp = skb->sp;
 225         if (sp) {
 226                 int i;
 227
 228                 for (i = sp->len - 1; i >= 0; i--) {
 229                         struct xfrm_state *x = sp->xvec[i];
 230                         if (selinux_authorizable_xfrm(x)) {
 231                                 struct xfrm_sec_ctx *ctx = x->security;
 232
 233                                 if (sid_session == SECSID_NULL) {
 234                                         sid_session = ctx->ctx_sid;
 235                                         if (!ckall)
 236                                                 goto out;
 237                                 } else if (sid_session != ctx->ctx_sid) {
 238                                         *sid = SECSID_NULL;
 239                                         return -EINVAL;
 240                                 }
 241                         }
 242                 }
 243         }
 244
 245 out:
 246         *sid = sid_session;
 247         return 0;
 248 }
 249
 250 /*
 251  * LSM hook implementation that allocs and transfers uctx spec to xfrm_policy.
 252  */
 253 int selinux_xfrm_policy_alloc(struct xfrm_sec_ctx **ctxp,
 254                               struct xfrm_user_sec_ctx *uctx)
 255 {
 256         return selinux_xfrm_alloc_user(ctxp, uctx);
 257 }
 258
 259 /*
 260  * LSM hook implementation that copies security data structure from old to new
 261  * for policy cloning.
 262  */
 263 int selinux_xfrm_policy_clone(struct xfrm_sec_ctx *old_ctx,
 264                               struct xfrm_sec_ctx **new_ctxp)
 265 {
 266         struct xfrm_sec_ctx *new_ctx;
 267
 268         if (!old_ctx)
 269                 return 0;
 270
 271         new_ctx = kmemdup(old_ctx, sizeof(*old_ctx) + old_ctx->ctx_len,
 272                           GFP_ATOMIC);
 273         if (!new_ctx)
 274                 return -ENOMEM;
 275         atomic_inc(&selinux_xfrm_refcount);
 276         *new_ctxp = new_ctx;
 277
 278         return 0;
 279 }
 280
 281 /*
 282  * LSM hook implementation that frees xfrm_sec_ctx security information.
 283  */
 284 void selinux_xfrm_policy_free(struct xfrm_sec_ctx *ctx)
 285 {
 286         selinux_xfrm_free(ctx);
 287 }
 288
 289 /*
 290  * LSM hook implementation that authorizes deletion of labeled policies.
 291  */
 292 int selinux_xfrm_policy_delete(struct xfrm_sec_ctx *ctx)
 293 {
 294         return selinux_xfrm_delete(ctx);
 295 }
 296
 297 /*
 298  * LSM hook implementation that allocates a xfrm_sec_state, populates it using
 299  * the supplied security context, and assigns it to the xfrm_state.
 300  */
 301 int selinux_xfrm_state_alloc(struct xfrm_state *x,
 302                              struct xfrm_user_sec_ctx *uctx)
 303 {
 304         return selinux_xfrm_alloc_user(&x->security, uctx);
 305 }
 306
 307 /*
 308  * LSM hook implementation that allocates a xfrm_sec_state and populates based
 309  * on a secid.
 310  */
 311 int selinux_xfrm_state_alloc_acquire(struct xfrm_state *x,
 312                                      struct xfrm_sec_ctx *polsec, u32 secid)
 313 {
 314         int rc;
 315         struct xfrm_sec_ctx *ctx;
 316         char *ctx_str = NULL;
 317         int str_len;
 318
 319         if (!polsec)
 320                 return 0;
 321
 322         if (secid == 0)
 323                 return -EINVAL;
 324
 325         rc = security_sid_to_context(secid, &ctx_str, &str_len);
 326         if (rc)
 327                 return rc;
 328
 329         ctx = kmalloc(sizeof(*ctx) + str_len, GFP_ATOMIC);
 330         if (!ctx) {
 331                 rc = -ENOMEM;
 332                 goto out;
 333         }
 334
 335         ctx->ctx_doi = XFRM_SC_DOI_LSM;
 336         ctx->ctx_alg = XFRM_SC_ALG_SELINUX;
 337         ctx->ctx_sid = secid;
 338         ctx->ctx_len = str_len;
 339         memcpy(ctx->ctx_str, ctx_str, str_len);
 340
 341         x->security = ctx;
 342         atomic_inc(&selinux_xfrm_refcount);
 343 out:
 344         kfree(ctx_str);
 345         return rc;
 346 }
 347
 348 /*
 349  * LSM hook implementation that frees xfrm_state security information.
 350  */
 351 void selinux_xfrm_state_free(struct xfrm_state *x)
 352 {
 353         selinux_xfrm_free(x->security);
 354 }
 355
 356 /*
 357  * LSM hook implementation that authorizes deletion of labeled SAs.
 358  */
 359 int selinux_xfrm_state_delete(struct xfrm_state *x)
 360 {
 361         return selinux_xfrm_delete(x->security);
 362 }
 363
 364 /*
 365  * LSM hook that controls access to unlabelled packets.  If
 366  * a xfrm_state is authorizable (defined by macro) then it was
 367  * already authorized by the IPSec process.  If not, then
 368  * we need to check for unlabelled access since this may not have
 369  * gone thru the IPSec process.
 370  */
 371 int selinux_xfrm_sock_rcv_skb(u32 sk_sid, struct sk_buff *skb,
 372                               struct common_audit_data *ad)
 373 {
 374         int i;
 375         struct sec_path *sp = skb->sp;
 376         u32 peer_sid = SECINITSID_UNLABELED;
 377
 378         if (sp) {
 379                 for (i = 0; i < sp->len; i++) {
 380                         struct xfrm_state *x = sp->xvec[i];
 381
 382                         if (x && selinux_authorizable_xfrm(x)) {
 383                                 struct xfrm_sec_ctx *ctx = x->security;
 384                                 peer_sid = ctx->ctx_sid;
 385                                 break;
 386                         }
 387                 }
 388         }
 389
 390         /* This check even when there's no association involved is intended,
 391          * according to Trent Jaeger, to make sure a process can't engage in
 392          * non-IPsec communication unless explicitly allowed by policy. */
 393         return avc_has_perm(sk_sid, peer_sid,
 394                             SECCLASS_ASSOCIATION, ASSOCIATION__RECVFROM, ad);
 395 }
 396
 397 /*
 398  * POSTROUTE_LAST hook's XFRM processing:
 399  * If we have no security association, then we need to determine
 400  * whether the socket is allowed to send to an unlabelled destination.
 401  * If we do have a authorizable security association, then it has already been
 402  * checked in the selinux_xfrm_state_pol_flow_match hook above.
 403  */
 404 int selinux_xfrm_postroute_last(u32 sk_sid, struct sk_buff *skb,
 405                                 struct common_audit_data *ad, u8 proto)
 406 {
 407         struct dst_entry *dst;
 408
 409         switch (proto) {
 410         case IPPROTO_AH:
 411         case IPPROTO_ESP:
 412         case IPPROTO_COMP:
 413                 /* We should have already seen this packet once before it
 414                  * underwent xfrm(s). No need to subject it to the unlabeled
 415                  * check. */
 416                 return 0;
 417         default:
 418                 break;
 419         }
 420
 421         dst = skb_dst(skb);
 422         if (dst) {
 423                 struct dst_entry *iter;
 424
 425                 for (iter = dst; iter != NULL; iter = iter->child) {
 426                         struct xfrm_state *x = iter->xfrm;
 427
 428                         if (x && selinux_authorizable_xfrm(x))
 429                                 return 0;
 430                 }
 431         }
 432
 433         /* This check even when there's no association involved is intended,
 434          * according to Trent Jaeger, to make sure a process can't engage in
 435          * non-IPsec communication unless explicitly allowed by policy. */
 436         return avc_has_perm(sk_sid, SECINITSID_UNLABELED,
 437                             SECCLASS_ASSOCIATION, ASSOCIATION__SENDTO, ad);
 438 }