xref: /linux/security/selinux/xfrm.c (revision ccae19c6239ae810242d2edc03b02bdcc12fc5ab)
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  *  Security-Enhanced Linux (SELinux) security module
4  *
5  *  This file contains the SELinux XFRM hook function implementations.
6  *
7  *  Authors:  Serge Hallyn <sergeh@us.ibm.com>
8  *	      Trent Jaeger <jaegert@us.ibm.com>
9  *
10  *  Updated: Venkat Yekkirala <vyekkirala@TrustedCS.com>
11  *
12  *           Granular IPSec Associations for use in MLS environments.
13  *
14  *  Copyright (C) 2005 International Business Machines Corporation
15  *  Copyright (C) 2006 Trusted Computer Solutions, Inc.
16  */
17 
18 /*
19  * USAGE:
20  * NOTES:
21  *   1. Make sure to enable the following options in your kernel config:
22  *	CONFIG_SECURITY=y
23  *	CONFIG_SECURITY_NETWORK=y
24  *	CONFIG_SECURITY_NETWORK_XFRM=y
25  *	CONFIG_SECURITY_SELINUX=m/y
26  * ISSUES:
27  *   1. Caching packets, so they are not dropped during negotiation
28  *   2. Emulating a reasonable SO_PEERSEC across machines
29  *   3. Testing addition of sk_policy's with security context via setsockopt
30  */
31 #include <linux/kernel.h>
32 #include <linux/init.h>
33 #include <linux/security.h>
34 #include <linux/types.h>
35 #include <linux/slab.h>
36 #include <linux/ip.h>
37 #include <linux/tcp.h>
38 #include <linux/skbuff.h>
39 #include <linux/xfrm.h>
40 #include <net/xfrm.h>
41 #include <net/checksum.h>
42 #include <net/udp.h>
43 #include <linux/atomic.h>
44 
45 #include "avc.h"
46 #include "objsec.h"
47 #include "xfrm.h"
48 
49 /* Labeled XFRM instance counter */
50 atomic_t selinux_xfrm_refcount __read_mostly = ATOMIC_INIT(0);
51 
52 /*
53  * Returns true if the context is an LSM/SELinux context.
54  */
selinux_authorizable_ctx(struct xfrm_sec_ctx * ctx)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  */
selinux_authorizable_xfrm(struct xfrm_state * x)65 static inline int selinux_authorizable_xfrm(struct xfrm_state *x)
66 {
67 	return selinux_authorizable_ctx(x->security);
68 }
69 
70 /*
71  * Allocates a xfrm_sec_state and populates it using the supplied security
72  * xfrm_user_sec_ctx context.
73  */
selinux_xfrm_alloc_user(struct xfrm_sec_ctx ** ctxp,struct xfrm_user_sec_ctx * uctx,gfp_t gfp)74 static int selinux_xfrm_alloc_user(struct xfrm_sec_ctx **ctxp,
75 				   struct xfrm_user_sec_ctx *uctx,
76 				   gfp_t gfp)
77 {
78 	int rc;
79 	struct xfrm_sec_ctx *ctx = NULL;
80 	u32 str_len;
81 
82 	if (ctxp == NULL || uctx == NULL ||
83 	    uctx->ctx_doi != XFRM_SC_DOI_LSM ||
84 	    uctx->ctx_alg != XFRM_SC_ALG_SELINUX)
85 		return -EINVAL;
86 
87 	str_len = uctx->ctx_len;
88 	if (str_len >= PAGE_SIZE)
89 		return -ENOMEM;
90 
91 	ctx = kmalloc(struct_size(ctx, ctx_str, str_len + 1), gfp);
92 	if (!ctx)
93 		return -ENOMEM;
94 
95 	ctx->ctx_doi = XFRM_SC_DOI_LSM;
96 	ctx->ctx_alg = XFRM_SC_ALG_SELINUX;
97 	ctx->ctx_len = str_len;
98 	memcpy(ctx->ctx_str, &uctx[1], str_len);
99 	ctx->ctx_str[str_len] = '\0';
100 	rc = security_context_to_sid(ctx->ctx_str, str_len,
101 				     &ctx->ctx_sid, gfp);
102 	if (rc)
103 		goto err;
104 
105 	rc = avc_has_perm(current_sid(), ctx->ctx_sid,
106 			  SECCLASS_ASSOCIATION, ASSOCIATION__SETCONTEXT, NULL);
107 	if (rc)
108 		goto err;
109 
110 	*ctxp = ctx;
111 	atomic_inc(&selinux_xfrm_refcount);
112 	return 0;
113 
114 err:
115 	kfree(ctx);
116 	return rc;
117 }
118 
119 /*
120  * Free the xfrm_sec_ctx structure.
121  */
selinux_xfrm_free(struct xfrm_sec_ctx * ctx)122 static void selinux_xfrm_free(struct xfrm_sec_ctx *ctx)
123 {
124 	if (!ctx)
125 		return;
126 
127 	atomic_dec(&selinux_xfrm_refcount);
128 	kfree(ctx);
129 }
130 
131 /*
132  * Authorize the deletion of a labeled SA or policy rule.
133  */
selinux_xfrm_delete(struct xfrm_sec_ctx * ctx)134 static int selinux_xfrm_delete(struct xfrm_sec_ctx *ctx)
135 {
136 	if (!ctx)
137 		return 0;
138 
139 	return avc_has_perm(current_sid(), ctx->ctx_sid,
140 			    SECCLASS_ASSOCIATION, ASSOCIATION__SETCONTEXT,
141 			    NULL);
142 }
143 
144 /*
145  * LSM hook implementation that authorizes that a flow can use a xfrm policy
146  * rule.
147  */
selinux_xfrm_policy_lookup(struct xfrm_sec_ctx * ctx,u32 fl_secid)148 int selinux_xfrm_policy_lookup(struct xfrm_sec_ctx *ctx, u32 fl_secid)
149 {
150 	int rc;
151 
152 	/* All flows should be treated as polmatch'ing an otherwise applicable
153 	 * "non-labeled" policy. This would prevent inadvertent "leaks". */
154 	if (!ctx)
155 		return 0;
156 
157 	/* Context sid is either set to label or ANY_ASSOC */
158 	if (!selinux_authorizable_ctx(ctx))
159 		return -EINVAL;
160 
161 	rc = avc_has_perm(fl_secid, ctx->ctx_sid,
162 			  SECCLASS_ASSOCIATION, ASSOCIATION__POLMATCH, NULL);
163 	return (rc == -EACCES ? -ESRCH : rc);
164 }
165 
166 /*
167  * LSM hook implementation that authorizes that a state matches
168  * the given policy, flow combo.
169  */
selinux_xfrm_state_pol_flow_match(struct xfrm_state * x,struct xfrm_policy * xp,const struct flowi_common * flic)170 int selinux_xfrm_state_pol_flow_match(struct xfrm_state *x,
171 				      struct xfrm_policy *xp,
172 				      const struct flowi_common *flic)
173 {
174 	u32 state_sid;
175 	u32 flic_sid;
176 
177 	if (!xp->security)
178 		if (x->security)
179 			/* unlabeled policy and labeled SA can't match */
180 			return 0;
181 		else
182 			/* unlabeled policy and unlabeled SA match all flows */
183 			return 1;
184 	else
185 		if (!x->security)
186 			/* unlabeled SA and labeled policy can't match */
187 			return 0;
188 		else
189 			if (!selinux_authorizable_xfrm(x))
190 				/* Not a SELinux-labeled SA */
191 				return 0;
192 
193 	state_sid = x->security->ctx_sid;
194 	flic_sid = flic->flowic_secid;
195 
196 	if (flic_sid != state_sid)
197 		return 0;
198 
199 	/* We don't need a separate SA Vs. policy polmatch check since the SA
200 	 * is now of the same label as the flow and a flow Vs. policy polmatch
201 	 * check had already happened in selinux_xfrm_policy_lookup() above. */
202 	return (avc_has_perm(flic_sid, state_sid,
203 			     SECCLASS_ASSOCIATION, ASSOCIATION__SENDTO,
204 			     NULL) ? 0 : 1);
205 }
206 
selinux_xfrm_skb_sid_egress(struct sk_buff * skb)207 static u32 selinux_xfrm_skb_sid_egress(struct sk_buff *skb)
208 {
209 	struct dst_entry *dst = skb_dst(skb);
210 	struct xfrm_state *x;
211 
212 	if (dst == NULL)
213 		return SECSID_NULL;
214 	x = dst->xfrm;
215 	if (x == NULL || !selinux_authorizable_xfrm(x))
216 		return SECSID_NULL;
217 
218 	return x->security->ctx_sid;
219 }
220 
selinux_xfrm_skb_sid_ingress(struct sk_buff * skb,u32 * sid,int ckall)221 static int selinux_xfrm_skb_sid_ingress(struct sk_buff *skb,
222 					u32 *sid, int ckall)
223 {
224 	u32 sid_session = SECSID_NULL;
225 	struct sec_path *sp = skb_sec_path(skb);
226 
227 	if (sp) {
228 		int i;
229 
230 		for (i = sp->len - 1; i >= 0; i--) {
231 			struct xfrm_state *x = sp->xvec[i];
232 			if (selinux_authorizable_xfrm(x)) {
233 				struct xfrm_sec_ctx *ctx = x->security;
234 
235 				if (sid_session == SECSID_NULL) {
236 					sid_session = ctx->ctx_sid;
237 					if (!ckall)
238 						goto out;
239 				} else if (sid_session != ctx->ctx_sid) {
240 					*sid = SECSID_NULL;
241 					return -EINVAL;
242 				}
243 			}
244 		}
245 	}
246 
247 out:
248 	*sid = sid_session;
249 	return 0;
250 }
251 
252 /*
253  * LSM hook implementation that checks and/or returns the xfrm sid for the
254  * incoming packet.
255  */
selinux_xfrm_decode_session(struct sk_buff * skb,u32 * sid,int ckall)256 int selinux_xfrm_decode_session(struct sk_buff *skb, u32 *sid, int ckall)
257 {
258 	if (skb == NULL) {
259 		*sid = SECSID_NULL;
260 		return 0;
261 	}
262 	return selinux_xfrm_skb_sid_ingress(skb, sid, ckall);
263 }
264 
selinux_xfrm_skb_sid(struct sk_buff * skb,u32 * sid)265 int selinux_xfrm_skb_sid(struct sk_buff *skb, u32 *sid)
266 {
267 	int rc;
268 
269 	rc = selinux_xfrm_skb_sid_ingress(skb, sid, 0);
270 	if (rc == 0 && *sid == SECSID_NULL)
271 		*sid = selinux_xfrm_skb_sid_egress(skb);
272 
273 	return rc;
274 }
275 
276 /*
277  * LSM hook implementation that allocs and transfers uctx spec to xfrm_policy.
278  */
selinux_xfrm_policy_alloc(struct xfrm_sec_ctx ** ctxp,struct xfrm_user_sec_ctx * uctx,gfp_t gfp)279 int selinux_xfrm_policy_alloc(struct xfrm_sec_ctx **ctxp,
280 			      struct xfrm_user_sec_ctx *uctx,
281 			      gfp_t gfp)
282 {
283 	return selinux_xfrm_alloc_user(ctxp, uctx, gfp);
284 }
285 
286 /*
287  * LSM hook implementation that copies security data structure from old to new
288  * for policy cloning.
289  */
selinux_xfrm_policy_clone(struct xfrm_sec_ctx * old_ctx,struct xfrm_sec_ctx ** new_ctxp)290 int selinux_xfrm_policy_clone(struct xfrm_sec_ctx *old_ctx,
291 			      struct xfrm_sec_ctx **new_ctxp)
292 {
293 	struct xfrm_sec_ctx *new_ctx;
294 
295 	if (!old_ctx)
296 		return 0;
297 
298 	new_ctx = kmemdup(old_ctx, sizeof(*old_ctx) + old_ctx->ctx_len,
299 			  GFP_ATOMIC);
300 	if (!new_ctx)
301 		return -ENOMEM;
302 	atomic_inc(&selinux_xfrm_refcount);
303 	*new_ctxp = new_ctx;
304 
305 	return 0;
306 }
307 
308 /*
309  * LSM hook implementation that frees xfrm_sec_ctx security information.
310  */
selinux_xfrm_policy_free(struct xfrm_sec_ctx * ctx)311 void selinux_xfrm_policy_free(struct xfrm_sec_ctx *ctx)
312 {
313 	selinux_xfrm_free(ctx);
314 }
315 
316 /*
317  * LSM hook implementation that authorizes deletion of labeled policies.
318  */
selinux_xfrm_policy_delete(struct xfrm_sec_ctx * ctx)319 int selinux_xfrm_policy_delete(struct xfrm_sec_ctx *ctx)
320 {
321 	return selinux_xfrm_delete(ctx);
322 }
323 
324 /*
325  * LSM hook implementation that allocates a xfrm_sec_state, populates it using
326  * the supplied security context, and assigns it to the xfrm_state.
327  */
selinux_xfrm_state_alloc(struct xfrm_state * x,struct xfrm_user_sec_ctx * uctx)328 int selinux_xfrm_state_alloc(struct xfrm_state *x,
329 			     struct xfrm_user_sec_ctx *uctx)
330 {
331 	return selinux_xfrm_alloc_user(&x->security, uctx, GFP_KERNEL);
332 }
333 
334 /*
335  * LSM hook implementation that allocates a xfrm_sec_state and populates based
336  * on a secid.
337  */
selinux_xfrm_state_alloc_acquire(struct xfrm_state * x,struct xfrm_sec_ctx * polsec,u32 secid)338 int selinux_xfrm_state_alloc_acquire(struct xfrm_state *x,
339 				     struct xfrm_sec_ctx *polsec, u32 secid)
340 {
341 	int rc;
342 	struct xfrm_sec_ctx *ctx;
343 	char *ctx_str = NULL;
344 	u32 str_len;
345 
346 	if (!polsec)
347 		return 0;
348 
349 	if (secid == 0)
350 		return -EINVAL;
351 
352 	rc = security_sid_to_context(secid, &ctx_str,
353 				     &str_len);
354 	if (rc)
355 		return rc;
356 
357 	ctx = kmalloc(struct_size(ctx, ctx_str, str_len), GFP_ATOMIC);
358 	if (!ctx) {
359 		rc = -ENOMEM;
360 		goto out;
361 	}
362 
363 	ctx->ctx_doi = XFRM_SC_DOI_LSM;
364 	ctx->ctx_alg = XFRM_SC_ALG_SELINUX;
365 	ctx->ctx_sid = secid;
366 	ctx->ctx_len = str_len;
367 	memcpy(ctx->ctx_str, ctx_str, str_len);
368 
369 	x->security = ctx;
370 	atomic_inc(&selinux_xfrm_refcount);
371 out:
372 	kfree(ctx_str);
373 	return rc;
374 }
375 
376 /*
377  * LSM hook implementation that frees xfrm_state security information.
378  */
selinux_xfrm_state_free(struct xfrm_state * x)379 void selinux_xfrm_state_free(struct xfrm_state *x)
380 {
381 	selinux_xfrm_free(x->security);
382 }
383 
384 /*
385  * LSM hook implementation that authorizes deletion of labeled SAs.
386  */
selinux_xfrm_state_delete(struct xfrm_state * x)387 int selinux_xfrm_state_delete(struct xfrm_state *x)
388 {
389 	return selinux_xfrm_delete(x->security);
390 }
391 
392 /*
393  * LSM hook that controls access to unlabelled packets.  If
394  * a xfrm_state is authorizable (defined by macro) then it was
395  * already authorized by the IPSec process.  If not, then
396  * we need to check for unlabelled access since this may not have
397  * gone thru the IPSec process.
398  */
selinux_xfrm_sock_rcv_skb(u32 sk_sid,struct sk_buff * skb,struct common_audit_data * ad)399 int selinux_xfrm_sock_rcv_skb(u32 sk_sid, struct sk_buff *skb,
400 			      struct common_audit_data *ad)
401 {
402 	int i;
403 	struct sec_path *sp = skb_sec_path(skb);
404 	u32 peer_sid = SECINITSID_UNLABELED;
405 
406 	if (sp) {
407 		for (i = 0; i < sp->len; i++) {
408 			struct xfrm_state *x = sp->xvec[i];
409 
410 			if (x && selinux_authorizable_xfrm(x)) {
411 				struct xfrm_sec_ctx *ctx = x->security;
412 				peer_sid = ctx->ctx_sid;
413 				break;
414 			}
415 		}
416 	}
417 
418 	/* This check even when there's no association involved is intended,
419 	 * according to Trent Jaeger, to make sure a process can't engage in
420 	 * non-IPsec communication unless explicitly allowed by policy. */
421 	return avc_has_perm(sk_sid, peer_sid,
422 			    SECCLASS_ASSOCIATION, ASSOCIATION__RECVFROM, ad);
423 }
424 
425 /*
426  * POSTROUTE_LAST hook's XFRM processing:
427  * If we have no security association, then we need to determine
428  * whether the socket is allowed to send to an unlabelled destination.
429  * If we do have a authorizable security association, then it has already been
430  * checked in the selinux_xfrm_state_pol_flow_match hook above.
431  */
selinux_xfrm_postroute_last(u32 sk_sid,struct sk_buff * skb,struct common_audit_data * ad,u8 proto)432 int selinux_xfrm_postroute_last(u32 sk_sid, struct sk_buff *skb,
433 				struct common_audit_data *ad, u8 proto)
434 {
435 	struct dst_entry *dst;
436 
437 	switch (proto) {
438 	case IPPROTO_AH:
439 	case IPPROTO_ESP:
440 	case IPPROTO_COMP:
441 		/* We should have already seen this packet once before it
442 		 * underwent xfrm(s). No need to subject it to the unlabeled
443 		 * check. */
444 		return 0;
445 	default:
446 		break;
447 	}
448 
449 	dst = skb_dst(skb);
450 	if (dst) {
451 		struct dst_entry *iter;
452 
453 		for (iter = dst; iter != NULL; iter = xfrm_dst_child(iter)) {
454 			struct xfrm_state *x = iter->xfrm;
455 
456 			if (x && selinux_authorizable_xfrm(x))
457 				return 0;
458 		}
459 	}
460 
461 	/* This check even when there's no association involved is intended,
462 	 * according to Trent Jaeger, to make sure a process can't engage in
463 	 * non-IPsec communication unless explicitly allowed by policy. */
464 	return avc_has_perm(sk_sid, SECINITSID_UNLABELED,
465 			    SECCLASS_ASSOCIATION, ASSOCIATION__SENDTO, ad);
466 }
467