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  *  Copyright (C) 2005 International Business Machines Corporation
  10  *
  11  *      This program is free software; you can redistribute it and/or modify
  12  *      it under the terms of the GNU General Public License version 2,
  13  *      as published by the Free Software Foundation.
  14  */
  15
  16 /*
  17  * USAGE:
  18  * NOTES:
  19  *   1. Make sure to enable the following options in your kernel config:
  20  *      CONFIG_SECURITY=y
  21  *      CONFIG_SECURITY_NETWORK=y
  22  *      CONFIG_SECURITY_NETWORK_XFRM=y
  23  *      CONFIG_SECURITY_SELINUX=m/y
  24  * ISSUES:
  25  *   1. Caching packets, so they are not dropped during negotiation
  26  *   2. Emulating a reasonable SO_PEERSEC across machines
  27  *   3. Testing addition of sk_policy's with security context via setsockopt
  28  */
  29 #include <linux/module.h>
  30 #include <linux/kernel.h>
  31 #include <linux/init.h>
  32 #include <linux/security.h>
  33 #include <linux/types.h>
  34 #include <linux/netfilter.h>
  35 #include <linux/netfilter_ipv4.h>
  36 #include <linux/netfilter_ipv6.h>
  37 #include <linux/ip.h>
  38 #include <linux/tcp.h>
  39 #include <linux/skbuff.h>
  40 #include <linux/xfrm.h>
  41 #include <net/xfrm.h>
  42 #include <net/checksum.h>
  43 #include <net/udp.h>
  44 #include <asm/semaphore.h>
  45
  46 #include "avc.h"
  47 #include "objsec.h"
  48 #include "xfrm.h"
  49
  50
  51 /*
  52  * Returns true if an LSM/SELinux context
  53  */
  54 static inline int selinux_authorizable_ctx(struct xfrm_sec_ctx *ctx)
  55 {
  56         return (ctx &&
  57                 (ctx->ctx_doi == XFRM_SC_DOI_LSM) &&
  58                 (ctx->ctx_alg == XFRM_SC_ALG_SELINUX));
  59 }
  60
  61 /*
  62  * Returns true if the xfrm contains a security blob for SELinux
  63  */
  64 static inline int selinux_authorizable_xfrm(struct xfrm_state *x)
  65 {
  66         return selinux_authorizable_ctx(x->security);
  67 }
  68
  69 /*
  70  * LSM hook implementation that authorizes that a socket can be used
  71  * with the corresponding xfrm_sec_ctx and direction.
  72  */
  73 int selinux_xfrm_policy_lookup(struct xfrm_policy *xp, u32 sk_sid, u8 dir)
  74 {
  75         int rc = 0;
  76         u32 sel_sid = SECINITSID_UNLABELED;
  77         struct xfrm_sec_ctx *ctx;
  78
  79         /* Context sid is either set to label or ANY_ASSOC */
  80         if ((ctx = xp->security)) {
  81                 if (!selinux_authorizable_ctx(ctx))
  82                         return -EINVAL;
  83
  84                 sel_sid = ctx->ctx_sid;
  85         }
  86
  87         rc = avc_has_perm(sk_sid, sel_sid, SECCLASS_ASSOCIATION,
  88                           ((dir == FLOW_DIR_IN) ? ASSOCIATION__RECVFROM :
  89                            ((dir == FLOW_DIR_OUT) ?  ASSOCIATION__SENDTO :
  90                             (ASSOCIATION__SENDTO | ASSOCIATION__RECVFROM))),
  91                           NULL);
  92
  93         return rc;
  94 }
  95
  96 /*
  97  * Security blob allocation for xfrm_policy and xfrm_state
  98  * CTX does not have a meaningful value on input
  99  */
 100 static int selinux_xfrm_sec_ctx_alloc(struct xfrm_sec_ctx **ctxp, struct xfrm_user_sec_ctx *uctx)
 101 {
 102         int rc = 0;
 103         struct task_security_struct *tsec = current->security;
 104         struct xfrm_sec_ctx *ctx;
 105
 106         BUG_ON(!uctx);
 107         BUG_ON(uctx->ctx_doi != XFRM_SC_ALG_SELINUX);
 108
 109         if (uctx->ctx_len >= PAGE_SIZE)
 110                 return -ENOMEM;
 111
 112         *ctxp = ctx = kmalloc(sizeof(*ctx) +
 113                               uctx->ctx_len,
 114                               GFP_KERNEL);
 115
 116         if (!ctx)
 117                 return -ENOMEM;
 118
 119         ctx->ctx_doi = uctx->ctx_doi;
 120         ctx->ctx_len = uctx->ctx_len;
 121         ctx->ctx_alg = uctx->ctx_alg;
 122
 123         memcpy(ctx->ctx_str,
 124                uctx+1,
 125                ctx->ctx_len);
 126         rc = security_context_to_sid(ctx->ctx_str,
 127                                      ctx->ctx_len,
 128                                      &ctx->ctx_sid);
 129
 130         if (rc)
 131                 goto out;
 132
 133         /*
 134          * Does the subject have permission to set security context?
 135          */
 136         rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
 137                           SECCLASS_ASSOCIATION,
 138                           ASSOCIATION__SETCONTEXT, NULL);
 139         if (rc)
 140                 goto out;
 141
 142         return rc;
 143
 144 out:
 145         *ctxp = NULL;
 146         kfree(ctx);
 147         return rc;
 148 }
 149
 150 /*
 151  * LSM hook implementation that allocs and transfers uctx spec to
 152  * xfrm_policy.
 153  */
 154 int selinux_xfrm_policy_alloc(struct xfrm_policy *xp, struct xfrm_user_sec_ctx *uctx)
 155 {
 156         int err;
 157
 158         BUG_ON(!xp);
 159
 160         err = selinux_xfrm_sec_ctx_alloc(&xp->security, uctx);
 161         return err;
 162 }
 163
 164
 165 /*
 166  * LSM hook implementation that copies security data structure from old to
 167  * new for policy cloning.
 168  */
 169 int selinux_xfrm_policy_clone(struct xfrm_policy *old, struct xfrm_policy *new)
 170 {
 171         struct xfrm_sec_ctx *old_ctx, *new_ctx;
 172
 173         old_ctx = old->security;
 174
 175         if (old_ctx) {
 176                 new_ctx = new->security = kmalloc(sizeof(*new_ctx) +
 177                                                   old_ctx->ctx_len,
 178                                                   GFP_KERNEL);
 179
 180                 if (!new_ctx)
 181                         return -ENOMEM;
 182
 183                 memcpy(new_ctx, old_ctx, sizeof(*new_ctx));
 184                 memcpy(new_ctx->ctx_str, old_ctx->ctx_str, new_ctx->ctx_len);
 185         }
 186         return 0;
 187 }
 188
 189 /*
 190  * LSM hook implementation that frees xfrm_policy security information.
 191  */
 192 void selinux_xfrm_policy_free(struct xfrm_policy *xp)
 193 {
 194         struct xfrm_sec_ctx *ctx = xp->security;
 195         if (ctx)
 196                 kfree(ctx);
 197 }
 198
 199 /*
 200  * LSM hook implementation that authorizes deletion of labeled policies.
 201  */
 202 int selinux_xfrm_policy_delete(struct xfrm_policy *xp)
 203 {
 204         struct task_security_struct *tsec = current->security;
 205         struct xfrm_sec_ctx *ctx = xp->security;
 206         int rc = 0;
 207
 208         if (ctx)
 209                 rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
 210                                   SECCLASS_ASSOCIATION,
 211                                   ASSOCIATION__SETCONTEXT, NULL);
 212
 213         return rc;
 214 }
 215
 216 /*
 217  * LSM hook implementation that allocs and transfers sec_ctx spec to
 218  * xfrm_state.
 219  */
 220 int selinux_xfrm_state_alloc(struct xfrm_state *x, struct xfrm_user_sec_ctx *uctx)
 221 {
 222         int err;
 223
 224         BUG_ON(!x);
 225
 226         err = selinux_xfrm_sec_ctx_alloc(&x->security, uctx);
 227         return err;
 228 }
 229
 230 /*
 231  * LSM hook implementation that frees xfrm_state security information.
 232  */
 233 void selinux_xfrm_state_free(struct xfrm_state *x)
 234 {
 235         struct xfrm_sec_ctx *ctx = x->security;
 236         if (ctx)
 237                 kfree(ctx);
 238 }
 239
 240 /*
 241  * SELinux internal function to retrieve the context of a connected
 242  * (sk->sk_state == TCP_ESTABLISHED) TCP socket based on its security
 243  * association used to connect to the remote socket.
 244  *
 245  * Retrieve via getsockopt SO_PEERSEC.
 246  */
 247 u32 selinux_socket_getpeer_stream(struct sock *sk)
 248 {
 249         struct dst_entry *dst, *dst_test;
 250         u32 peer_sid = SECSID_NULL;
 251
 252         if (sk->sk_state != TCP_ESTABLISHED)
 253                 goto out;
 254
 255         dst = sk_dst_get(sk);
 256         if (!dst)
 257                 goto out;
 258
 259         for (dst_test = dst; dst_test != 0;
 260              dst_test = dst_test->child) {
 261                 struct xfrm_state *x = dst_test->xfrm;
 262
 263                 if (x && selinux_authorizable_xfrm(x)) {
 264                         struct xfrm_sec_ctx *ctx = x->security;
 265                         peer_sid = ctx->ctx_sid;
 266                         break;
 267                 }
 268         }
 269         dst_release(dst);
 270
 271 out:
 272         return peer_sid;
 273 }
 274
 275 /*
 276  * SELinux internal function to retrieve the context of a UDP packet
 277  * based on its security association used to connect to the remote socket.
 278  *
 279  * Retrieve via setsockopt IP_PASSSEC and recvmsg with control message
 280  * type SCM_SECURITY.
 281  */
 282 u32 selinux_socket_getpeer_dgram(struct sk_buff *skb)
 283 {
 284         struct sec_path *sp;
 285
 286         if (skb == NULL)
 287                 return SECSID_NULL;
 288
 289         if (skb->sk->sk_protocol != IPPROTO_UDP)
 290                 return SECSID_NULL;
 291
 292         sp = skb->sp;
 293         if (sp) {
 294                 int i;
 295
 296                 for (i = sp->len-1; i >= 0; i--) {
 297                         struct xfrm_state *x = sp->xvec[i];
 298                         if (selinux_authorizable_xfrm(x)) {
 299                                 struct xfrm_sec_ctx *ctx = x->security;
 300                                 return ctx->ctx_sid;
 301                         }
 302                 }
 303         }
 304
 305         return SECSID_NULL;
 306 }
 307
 308  /*
 309   * LSM hook implementation that authorizes deletion of labeled SAs.
 310   */
 311 int selinux_xfrm_state_delete(struct xfrm_state *x)
 312 {
 313         struct task_security_struct *tsec = current->security;
 314         struct xfrm_sec_ctx *ctx = x->security;
 315         int rc = 0;
 316
 317         if (ctx)
 318                 rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
 319                                   SECCLASS_ASSOCIATION,
 320                                   ASSOCIATION__SETCONTEXT, NULL);
 321
 322         return rc;
 323 }
 324
 325 /*
 326  * LSM hook that controls access to unlabelled packets.  If
 327  * a xfrm_state is authorizable (defined by macro) then it was
 328  * already authorized by the IPSec process.  If not, then
 329  * we need to check for unlabelled access since this may not have
 330  * gone thru the IPSec process.
 331  */
 332 int selinux_xfrm_sock_rcv_skb(u32 isec_sid, struct sk_buff *skb)
 333 {
 334         int i, rc = 0;
 335         struct sec_path *sp;
 336
 337         sp = skb->sp;
 338
 339         if (sp) {
 340                 /*
 341                  * __xfrm_policy_check does not approve unless xfrm_policy_ok
 342                  * says that spi's match for policy and the socket.
 343                  *
 344                  *  Only need to verify the existence of an authorizable sp.
 345                  */
 346                 for (i = 0; i < sp->len; i++) {
 347                         struct xfrm_state *x = sp->xvec[i];
 348
 349                         if (x && selinux_authorizable_xfrm(x))
 350                                 goto accept;
 351                 }
 352         }
 353
 354         /* check SELinux sock for unlabelled access */
 355         rc = avc_has_perm(isec_sid, SECINITSID_UNLABELED, SECCLASS_ASSOCIATION,
 356                           ASSOCIATION__RECVFROM, NULL);
 357         if (rc)
 358                 goto drop;
 359
 360 accept:
 361         return 0;
 362
 363 drop:
 364         return rc;
 365 }
 366
 367 /*
 368  * POSTROUTE_LAST hook's XFRM processing:
 369  * If we have no security association, then we need to determine
 370  * whether the socket is allowed to send to an unlabelled destination.
 371  * If we do have a authorizable security association, then it has already been
 372  * checked in xfrm_policy_lookup hook.
 373  */
 374 int selinux_xfrm_postroute_last(u32 isec_sid, struct sk_buff *skb)
 375 {
 376         struct dst_entry *dst;
 377         int rc = 0;
 378
 379         dst = skb->dst;
 380
 381         if (dst) {
 382                 struct dst_entry *dst_test;
 383
 384                 for (dst_test = dst; dst_test != 0;
 385                      dst_test = dst_test->child) {
 386                         struct xfrm_state *x = dst_test->xfrm;
 387
 388                         if (x && selinux_authorizable_xfrm(x))
 389                                 goto out;
 390                 }
 391         }
 392
 393         rc = avc_has_perm(isec_sid, SECINITSID_UNLABELED, SECCLASS_ASSOCIATION,
 394                           ASSOCIATION__SENDTO, NULL);
 395 out:
 396         return rc;
 397 }