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Linux/security/selinux/xfrm.c

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

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