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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                                    gfp_t gfp)
 83 {
 84         int rc;
 85         const struct task_security_struct *tsec = current_security();
 86         struct xfrm_sec_ctx *ctx = NULL;
 87         u32 str_len;
 88 
 89         if (ctxp == NULL || uctx == NULL ||
 90             uctx->ctx_doi != XFRM_SC_DOI_LSM ||
 91             uctx->ctx_alg != XFRM_SC_ALG_SELINUX)
 92                 return -EINVAL;
 93 
 94         str_len = uctx->ctx_len;
 95         if (str_len >= PAGE_SIZE)
 96                 return -ENOMEM;
 97 
 98         ctx = kmalloc(sizeof(*ctx) + str_len + 1, gfp);
 99         if (!ctx)
100                 return -ENOMEM;
101 
102         ctx->ctx_doi = XFRM_SC_DOI_LSM;
103         ctx->ctx_alg = XFRM_SC_ALG_SELINUX;
104         ctx->ctx_len = str_len;
105         memcpy(ctx->ctx_str, &uctx[1], str_len);
106         ctx->ctx_str[str_len] = '\0';
107         rc = security_context_to_sid(ctx->ctx_str, str_len, &ctx->ctx_sid, gfp);
108         if (rc)
109                 goto err;
110 
111         rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
112                           SECCLASS_ASSOCIATION, ASSOCIATION__SETCONTEXT, NULL);
113         if (rc)
114                 goto err;
115 
116         *ctxp = ctx;
117         atomic_inc(&selinux_xfrm_refcount);
118         return 0;
119 
120 err:
121         kfree(ctx);
122         return rc;
123 }
124 
125 /*
126  * Free the xfrm_sec_ctx structure.
127  */
128 static void selinux_xfrm_free(struct xfrm_sec_ctx *ctx)
129 {
130         if (!ctx)
131                 return;
132 
133         atomic_dec(&selinux_xfrm_refcount);
134         kfree(ctx);
135 }
136 
137 /*
138  * Authorize the deletion of a labeled SA or policy rule.
139  */
140 static int selinux_xfrm_delete(struct xfrm_sec_ctx *ctx)
141 {
142         const struct task_security_struct *tsec = current_security();
143 
144         if (!ctx)
145                 return 0;
146 
147         return avc_has_perm(tsec->sid, ctx->ctx_sid,
148                             SECCLASS_ASSOCIATION, ASSOCIATION__SETCONTEXT,
149                             NULL);
150 }
151 
152 /*
153  * LSM hook implementation that authorizes that a flow can use a xfrm policy
154  * rule.
155  */
156 int selinux_xfrm_policy_lookup(struct xfrm_sec_ctx *ctx, u32 fl_secid, u8 dir)
157 {
158         int rc;
159 
160         /* All flows should be treated as polmatch'ing an otherwise applicable
161          * "non-labeled" policy. This would prevent inadvertent "leaks". */
162         if (!ctx)
163                 return 0;
164 
165         /* Context sid is either set to label or ANY_ASSOC */
166         if (!selinux_authorizable_ctx(ctx))
167                 return -EINVAL;
168 
169         rc = avc_has_perm(fl_secid, ctx->ctx_sid,
170                           SECCLASS_ASSOCIATION, ASSOCIATION__POLMATCH, NULL);
171         return (rc == -EACCES ? -ESRCH : rc);
172 }
173 
174 /*
175  * LSM hook implementation that authorizes that a state matches
176  * the given policy, flow combo.
177  */
178 int selinux_xfrm_state_pol_flow_match(struct xfrm_state *x,
179                                       struct xfrm_policy *xp,
180                                       const struct flowi *fl)
181 {
182         u32 state_sid;
183 
184         if (!xp->security)
185                 if (x->security)
186                         /* unlabeled policy and labeled SA can't match */
187                         return 0;
188                 else
189                         /* unlabeled policy and unlabeled SA match all flows */
190                         return 1;
191         else
192                 if (!x->security)
193                         /* unlabeled SA and labeled policy can't match */
194                         return 0;
195                 else
196                         if (!selinux_authorizable_xfrm(x))
197                                 /* Not a SELinux-labeled SA */
198                                 return 0;
199 
200         state_sid = x->security->ctx_sid;
201 
202         if (fl->flowi_secid != state_sid)
203                 return 0;
204 
205         /* We don't need a separate SA Vs. policy polmatch check since the SA
206          * is now of the same label as the flow and a flow Vs. policy polmatch
207          * check had already happened in selinux_xfrm_policy_lookup() above. */
208         return (avc_has_perm(fl->flowi_secid, state_sid,
209                             SECCLASS_ASSOCIATION, ASSOCIATION__SENDTO,
210                             NULL) ? 0 : 1);
211 }
212 
213 static u32 selinux_xfrm_skb_sid_egress(struct sk_buff *skb)
214 {
215         struct dst_entry *dst = skb_dst(skb);
216         struct xfrm_state *x;
217 
218         if (dst == NULL)
219                 return SECSID_NULL;
220         x = dst->xfrm;
221         if (x == NULL || !selinux_authorizable_xfrm(x))
222                 return SECSID_NULL;
223 
224         return x->security->ctx_sid;
225 }
226 
227 static int selinux_xfrm_skb_sid_ingress(struct sk_buff *skb,
228                                         u32 *sid, int ckall)
229 {
230         u32 sid_session = SECSID_NULL;
231         struct sec_path *sp = skb->sp;
232 
233         if (sp) {
234                 int i;
235 
236                 for (i = sp->len - 1; i >= 0; i--) {
237                         struct xfrm_state *x = sp->xvec[i];
238                         if (selinux_authorizable_xfrm(x)) {
239                                 struct xfrm_sec_ctx *ctx = x->security;
240 
241                                 if (sid_session == SECSID_NULL) {
242                                         sid_session = ctx->ctx_sid;
243                                         if (!ckall)
244                                                 goto out;
245                                 } else if (sid_session != ctx->ctx_sid) {
246                                         *sid = SECSID_NULL;
247                                         return -EINVAL;
248                                 }
249                         }
250                 }
251         }
252 
253 out:
254         *sid = sid_session;
255         return 0;
256 }
257 
258 /*
259  * LSM hook implementation that checks and/or returns the xfrm sid for the
260  * incoming packet.
261  */
262 int selinux_xfrm_decode_session(struct sk_buff *skb, u32 *sid, int ckall)
263 {
264         if (skb == NULL) {
265                 *sid = SECSID_NULL;
266                 return 0;
267         }
268         return selinux_xfrm_skb_sid_ingress(skb, sid, ckall);
269 }
270 
271 int selinux_xfrm_skb_sid(struct sk_buff *skb, u32 *sid)
272 {
273         int rc;
274 
275         rc = selinux_xfrm_skb_sid_ingress(skb, sid, 0);
276         if (rc == 0 && *sid == SECSID_NULL)
277                 *sid = selinux_xfrm_skb_sid_egress(skb);
278 
279         return rc;
280 }
281 
282 /*
283  * LSM hook implementation that allocs and transfers uctx spec to xfrm_policy.
284  */
285 int selinux_xfrm_policy_alloc(struct xfrm_sec_ctx **ctxp,
286                               struct xfrm_user_sec_ctx *uctx,
287                               gfp_t gfp)
288 {
289         return selinux_xfrm_alloc_user(ctxp, uctx, gfp);
290 }
291 
292 /*
293  * LSM hook implementation that copies security data structure from old to new
294  * for policy cloning.
295  */
296 int selinux_xfrm_policy_clone(struct xfrm_sec_ctx *old_ctx,
297                               struct xfrm_sec_ctx **new_ctxp)
298 {
299         struct xfrm_sec_ctx *new_ctx;
300 
301         if (!old_ctx)
302                 return 0;
303 
304         new_ctx = kmemdup(old_ctx, sizeof(*old_ctx) + old_ctx->ctx_len,
305                           GFP_ATOMIC);
306         if (!new_ctx)
307                 return -ENOMEM;
308         atomic_inc(&selinux_xfrm_refcount);
309         *new_ctxp = new_ctx;
310 
311         return 0;
312 }
313 
314 /*
315  * LSM hook implementation that frees xfrm_sec_ctx security information.
316  */
317 void selinux_xfrm_policy_free(struct xfrm_sec_ctx *ctx)
318 {
319         selinux_xfrm_free(ctx);
320 }
321 
322 /*
323  * LSM hook implementation that authorizes deletion of labeled policies.
324  */
325 int selinux_xfrm_policy_delete(struct xfrm_sec_ctx *ctx)
326 {
327         return selinux_xfrm_delete(ctx);
328 }
329 
330 /*
331  * LSM hook implementation that allocates a xfrm_sec_state, populates it using
332  * the supplied security context, and assigns it to the xfrm_state.
333  */
334 int selinux_xfrm_state_alloc(struct xfrm_state *x,
335                              struct xfrm_user_sec_ctx *uctx)
336 {
337         return selinux_xfrm_alloc_user(&x->security, uctx, GFP_KERNEL);
338 }
339 
340 /*
341  * LSM hook implementation that allocates a xfrm_sec_state and populates based
342  * on a secid.
343  */
344 int selinux_xfrm_state_alloc_acquire(struct xfrm_state *x,
345                                      struct xfrm_sec_ctx *polsec, u32 secid)
346 {
347         int rc;
348         struct xfrm_sec_ctx *ctx;
349         char *ctx_str = NULL;
350         int str_len;
351 
352         if (!polsec)
353                 return 0;
354 
355         if (secid == 0)
356                 return -EINVAL;
357 
358         rc = security_sid_to_context(secid, &ctx_str, &str_len);
359         if (rc)
360                 return rc;
361 
362         ctx = kmalloc(sizeof(*ctx) + str_len, GFP_ATOMIC);
363         if (!ctx) {
364                 rc = -ENOMEM;
365                 goto out;
366         }
367 
368         ctx->ctx_doi = XFRM_SC_DOI_LSM;
369         ctx->ctx_alg = XFRM_SC_ALG_SELINUX;
370         ctx->ctx_sid = secid;
371         ctx->ctx_len = str_len;
372         memcpy(ctx->ctx_str, ctx_str, str_len);
373 
374         x->security = ctx;
375         atomic_inc(&selinux_xfrm_refcount);
376 out:
377         kfree(ctx_str);
378         return rc;
379 }
380 
381 /*
382  * LSM hook implementation that frees xfrm_state security information.
383  */
384 void selinux_xfrm_state_free(struct xfrm_state *x)
385 {
386         selinux_xfrm_free(x->security);
387 }
388 
389 /*
390  * LSM hook implementation that authorizes deletion of labeled SAs.
391  */
392 int selinux_xfrm_state_delete(struct xfrm_state *x)
393 {
394         return selinux_xfrm_delete(x->security);
395 }
396 
397 /*
398  * LSM hook that controls access to unlabelled packets.  If
399  * a xfrm_state is authorizable (defined by macro) then it was
400  * already authorized by the IPSec process.  If not, then
401  * we need to check for unlabelled access since this may not have
402  * gone thru the IPSec process.
403  */
404 int selinux_xfrm_sock_rcv_skb(u32 sk_sid, struct sk_buff *skb,
405                               struct common_audit_data *ad)
406 {
407         int i;
408         struct sec_path *sp = skb->sp;
409         u32 peer_sid = SECINITSID_UNLABELED;
410 
411         if (sp) {
412                 for (i = 0; i < sp->len; i++) {
413                         struct xfrm_state *x = sp->xvec[i];
414 
415                         if (x && selinux_authorizable_xfrm(x)) {
416                                 struct xfrm_sec_ctx *ctx = x->security;
417                                 peer_sid = ctx->ctx_sid;
418                                 break;
419                         }
420                 }
421         }
422 
423         /* This check even when there's no association involved is intended,
424          * according to Trent Jaeger, to make sure a process can't engage in
425          * non-IPsec communication unless explicitly allowed by policy. */
426         return avc_has_perm(sk_sid, peer_sid,
427                             SECCLASS_ASSOCIATION, ASSOCIATION__RECVFROM, ad);
428 }
429 
430 /*
431  * POSTROUTE_LAST hook's XFRM processing:
432  * If we have no security association, then we need to determine
433  * whether the socket is allowed to send to an unlabelled destination.
434  * If we do have a authorizable security association, then it has already been
435  * checked in the selinux_xfrm_state_pol_flow_match hook above.
436  */
437 int selinux_xfrm_postroute_last(u32 sk_sid, struct sk_buff *skb,
438                                 struct common_audit_data *ad, u8 proto)
439 {
440         struct dst_entry *dst;
441 
442         switch (proto) {
443         case IPPROTO_AH:
444         case IPPROTO_ESP:
445         case IPPROTO_COMP:
446                 /* We should have already seen this packet once before it
447                  * underwent xfrm(s). No need to subject it to the unlabeled
448                  * check. */
449                 return 0;
450         default:
451                 break;
452         }
453 
454         dst = skb_dst(skb);
455         if (dst) {
456                 struct dst_entry *iter;
457 
458                 for (iter = dst; iter != NULL; iter = iter->child) {
459                         struct xfrm_state *x = iter->xfrm;
460 
461                         if (x && selinux_authorizable_xfrm(x))
462                                 return 0;
463                 }
464         }
465 
466         /* This check even when there's no association involved is intended,
467          * according to Trent Jaeger, to make sure a process can't engage in
468          * non-IPsec communication unless explicitly allowed by policy. */
469         return avc_has_perm(sk_sid, SECINITSID_UNLABELED,
470                             SECCLASS_ASSOCIATION, ASSOCIATION__SENDTO, ad);
471 }
472 

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