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