1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  *  NSA 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 	const struct task_security_struct *tsec = selinux_cred(current_cred());
80 	struct xfrm_sec_ctx *ctx = NULL;
81 	u32 str_len;
82 
83 	if (ctxp == NULL || uctx == NULL ||
84 	    uctx->ctx_doi != XFRM_SC_DOI_LSM ||
85 	    uctx->ctx_alg != XFRM_SC_ALG_SELINUX)
86 		return -EINVAL;
87 
88 	str_len = uctx->ctx_len;
89 	if (str_len >= PAGE_SIZE)
90 		return -ENOMEM;
91 
92 	ctx = kmalloc(struct_size(ctx, ctx_str, str_len + 1), gfp);
93 	if (!ctx)
94 		return -ENOMEM;
95 
96 	ctx->ctx_doi = XFRM_SC_DOI_LSM;
97 	ctx->ctx_alg = XFRM_SC_ALG_SELINUX;
98 	ctx->ctx_len = str_len;
99 	memcpy(ctx->ctx_str, &uctx[1], str_len);
100 	ctx->ctx_str[str_len] = '\0';
101 	rc = security_context_to_sid(&selinux_state, ctx->ctx_str, str_len,
102 				     &ctx->ctx_sid, gfp);
103 	if (rc)
104 		goto err;
105 
106 	rc = avc_has_perm(&selinux_state,
107 			  tsec->sid, ctx->ctx_sid,
108 			  SECCLASS_ASSOCIATION, ASSOCIATION__SETCONTEXT, NULL);
109 	if (rc)
110 		goto err;
111 
112 	*ctxp = ctx;
113 	atomic_inc(&selinux_xfrm_refcount);
114 	return 0;
115 
116 err:
117 	kfree(ctx);
118 	return rc;
119 }
120 
121 /*
122  * Free the xfrm_sec_ctx structure.
123  */
selinux_xfrm_free(struct xfrm_sec_ctx * ctx)124 static void selinux_xfrm_free(struct xfrm_sec_ctx *ctx)
125 {
126 	if (!ctx)
127 		return;
128 
129 	atomic_dec(&selinux_xfrm_refcount);
130 	kfree(ctx);
131 }
132 
133 /*
134  * Authorize the deletion of a labeled SA or policy rule.
135  */
selinux_xfrm_delete(struct xfrm_sec_ctx * ctx)136 static int selinux_xfrm_delete(struct xfrm_sec_ctx *ctx)
137 {
138 	const struct task_security_struct *tsec = selinux_cred(current_cred());
139 
140 	if (!ctx)
141 		return 0;
142 
143 	return avc_has_perm(&selinux_state,
144 			    tsec->sid, ctx->ctx_sid,
145 			    SECCLASS_ASSOCIATION, ASSOCIATION__SETCONTEXT,
146 			    NULL);
147 }
148 
149 /*
150  * LSM hook implementation that authorizes that a flow can use a xfrm policy
151  * rule.
152  */
selinux_xfrm_policy_lookup(struct xfrm_sec_ctx * ctx,u32 fl_secid)153 int selinux_xfrm_policy_lookup(struct xfrm_sec_ctx *ctx, u32 fl_secid)
154 {
155 	int rc;
156 
157 	/* All flows should be treated as polmatch'ing an otherwise applicable
158 	 * "non-labeled" policy. This would prevent inadvertent "leaks". */
159 	if (!ctx)
160 		return 0;
161 
162 	/* Context sid is either set to label or ANY_ASSOC */
163 	if (!selinux_authorizable_ctx(ctx))
164 		return -EINVAL;
165 
166 	rc = avc_has_perm(&selinux_state,
167 			  fl_secid, ctx->ctx_sid,
168 			  SECCLASS_ASSOCIATION, ASSOCIATION__POLMATCH, NULL);
169 	return (rc == -EACCES ? -ESRCH : rc);
170 }
171 
172 /*
173  * LSM hook implementation that authorizes that a state matches
174  * the given policy, flow combo.
175  */
selinux_xfrm_state_pol_flow_match(struct xfrm_state * x,struct xfrm_policy * xp,const struct flowi_common * flic)176 int selinux_xfrm_state_pol_flow_match(struct xfrm_state *x,
177 				      struct xfrm_policy *xp,
178 				      const struct flowi_common *flic)
179 {
180 	u32 state_sid;
181 	u32 flic_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 	flic_sid = flic->flowic_secid;
201 
202 	if (flic_sid != 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(&selinux_state, flic_sid, state_sid,
209 			     SECCLASS_ASSOCIATION, ASSOCIATION__SENDTO,
210 			     NULL) ? 0 : 1);
211 }
212 
selinux_xfrm_skb_sid_egress(struct sk_buff * skb)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 
selinux_xfrm_skb_sid_ingress(struct sk_buff * skb,u32 * sid,int ckall)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_sec_path(skb);
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  */
selinux_xfrm_decode_session(struct sk_buff * skb,u32 * sid,int ckall)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 
selinux_xfrm_skb_sid(struct sk_buff * skb,u32 * sid)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  */
selinux_xfrm_policy_alloc(struct xfrm_sec_ctx ** ctxp,struct xfrm_user_sec_ctx * uctx,gfp_t gfp)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  */
selinux_xfrm_policy_clone(struct xfrm_sec_ctx * old_ctx,struct xfrm_sec_ctx ** new_ctxp)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  */
selinux_xfrm_policy_free(struct xfrm_sec_ctx * ctx)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  */
selinux_xfrm_policy_delete(struct xfrm_sec_ctx * ctx)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  */
selinux_xfrm_state_alloc(struct xfrm_state * x,struct xfrm_user_sec_ctx * uctx)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  */
selinux_xfrm_state_alloc_acquire(struct xfrm_state * x,struct xfrm_sec_ctx * polsec,u32 secid)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 	u32 str_len;
351 
352 	if (!polsec)
353 		return 0;
354 
355 	if (secid == 0)
356 		return -EINVAL;
357 
358 	rc = security_sid_to_context(&selinux_state, secid, &ctx_str,
359 				     &str_len);
360 	if (rc)
361 		return rc;
362 
363 	ctx = kmalloc(struct_size(ctx, ctx_str, str_len), GFP_ATOMIC);
364 	if (!ctx) {
365 		rc = -ENOMEM;
366 		goto out;
367 	}
368 
369 	ctx->ctx_doi = XFRM_SC_DOI_LSM;
370 	ctx->ctx_alg = XFRM_SC_ALG_SELINUX;
371 	ctx->ctx_sid = secid;
372 	ctx->ctx_len = str_len;
373 	memcpy(ctx->ctx_str, ctx_str, str_len);
374 
375 	x->security = ctx;
376 	atomic_inc(&selinux_xfrm_refcount);
377 out:
378 	kfree(ctx_str);
379 	return rc;
380 }
381 
382 /*
383  * LSM hook implementation that frees xfrm_state security information.
384  */
selinux_xfrm_state_free(struct xfrm_state * x)385 void selinux_xfrm_state_free(struct xfrm_state *x)
386 {
387 	selinux_xfrm_free(x->security);
388 }
389 
390 /*
391  * LSM hook implementation that authorizes deletion of labeled SAs.
392  */
selinux_xfrm_state_delete(struct xfrm_state * x)393 int selinux_xfrm_state_delete(struct xfrm_state *x)
394 {
395 	return selinux_xfrm_delete(x->security);
396 }
397 
398 /*
399  * LSM hook that controls access to unlabelled packets.  If
400  * a xfrm_state is authorizable (defined by macro) then it was
401  * already authorized by the IPSec process.  If not, then
402  * we need to check for unlabelled access since this may not have
403  * gone thru the IPSec process.
404  */
selinux_xfrm_sock_rcv_skb(u32 sk_sid,struct sk_buff * skb,struct common_audit_data * ad)405 int selinux_xfrm_sock_rcv_skb(u32 sk_sid, struct sk_buff *skb,
406 			      struct common_audit_data *ad)
407 {
408 	int i;
409 	struct sec_path *sp = skb_sec_path(skb);
410 	u32 peer_sid = SECINITSID_UNLABELED;
411 
412 	if (sp) {
413 		for (i = 0; i < sp->len; i++) {
414 			struct xfrm_state *x = sp->xvec[i];
415 
416 			if (x && selinux_authorizable_xfrm(x)) {
417 				struct xfrm_sec_ctx *ctx = x->security;
418 				peer_sid = ctx->ctx_sid;
419 				break;
420 			}
421 		}
422 	}
423 
424 	/* This check even when there's no association involved is intended,
425 	 * according to Trent Jaeger, to make sure a process can't engage in
426 	 * non-IPsec communication unless explicitly allowed by policy. */
427 	return avc_has_perm(&selinux_state,
428 			    sk_sid, peer_sid,
429 			    SECCLASS_ASSOCIATION, ASSOCIATION__RECVFROM, ad);
430 }
431 
432 /*
433  * POSTROUTE_LAST hook's XFRM processing:
434  * If we have no security association, then we need to determine
435  * whether the socket is allowed to send to an unlabelled destination.
436  * If we do have a authorizable security association, then it has already been
437  * checked in the selinux_xfrm_state_pol_flow_match hook above.
438  */
selinux_xfrm_postroute_last(u32 sk_sid,struct sk_buff * skb,struct common_audit_data * ad,u8 proto)439 int selinux_xfrm_postroute_last(u32 sk_sid, struct sk_buff *skb,
440 				struct common_audit_data *ad, u8 proto)
441 {
442 	struct dst_entry *dst;
443 
444 	switch (proto) {
445 	case IPPROTO_AH:
446 	case IPPROTO_ESP:
447 	case IPPROTO_COMP:
448 		/* We should have already seen this packet once before it
449 		 * underwent xfrm(s). No need to subject it to the unlabeled
450 		 * check. */
451 		return 0;
452 	default:
453 		break;
454 	}
455 
456 	dst = skb_dst(skb);
457 	if (dst) {
458 		struct dst_entry *iter;
459 
460 		for (iter = dst; iter != NULL; iter = xfrm_dst_child(iter)) {
461 			struct xfrm_state *x = iter->xfrm;
462 
463 			if (x && selinux_authorizable_xfrm(x))
464 				return 0;
465 		}
466 	}
467 
468 	/* This check even when there's no association involved is intended,
469 	 * according to Trent Jaeger, to make sure a process can't engage in
470 	 * non-IPsec communication unless explicitly allowed by policy. */
471 	return avc_has_perm(&selinux_state, sk_sid, SECINITSID_UNLABELED,
472 			    SECCLASS_ASSOCIATION, ASSOCIATION__SENDTO, ad);
473 }
474