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 */
50atomic_t selinux_xfrm_refcount __read_mostly = ATOMIC_INIT(0);
51
52/*
53 * Returns true if the context is an LSM/SELinux context.
54 */
55static 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 */
65static 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 */
74static 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(ctx->ctx_str, str_len,
102				     &ctx->ctx_sid, gfp);
103	if (rc)
104		goto err;
105
106	rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
107			  SECCLASS_ASSOCIATION, ASSOCIATION__SETCONTEXT, NULL);
108	if (rc)
109		goto err;
110
111	*ctxp = ctx;
112	atomic_inc(&selinux_xfrm_refcount);
113	return 0;
114
115err:
116	kfree(ctx);
117	return rc;
118}
119
120/*
121 * Free the xfrm_sec_ctx structure.
122 */
123static void selinux_xfrm_free(struct xfrm_sec_ctx *ctx)
124{
125	if (!ctx)
126		return;
127
128	atomic_dec(&selinux_xfrm_refcount);
129	kfree(ctx);
130}
131
132/*
133 * Authorize the deletion of a labeled SA or policy rule.
134 */
135static int selinux_xfrm_delete(struct xfrm_sec_ctx *ctx)
136{
137	const struct task_security_struct *tsec = selinux_cred(current_cred());
138
139	if (!ctx)
140		return 0;
141
142	return avc_has_perm(tsec->sid, ctx->ctx_sid,
143			    SECCLASS_ASSOCIATION, ASSOCIATION__SETCONTEXT,
144			    NULL);
145}
146
147/*
148 * LSM hook implementation that authorizes that a flow can use a xfrm policy
149 * rule.
150 */
151int selinux_xfrm_policy_lookup(struct xfrm_sec_ctx *ctx, u32 fl_secid)
152{
153	int rc;
154
155	/* All flows should be treated as polmatch'ing an otherwise applicable
156	 * "non-labeled" policy. This would prevent inadvertent "leaks". */
157	if (!ctx)
158		return 0;
159
160	/* Context sid is either set to label or ANY_ASSOC */
161	if (!selinux_authorizable_ctx(ctx))
162		return -EINVAL;
163
164	rc = avc_has_perm(fl_secid, ctx->ctx_sid,
165			  SECCLASS_ASSOCIATION, ASSOCIATION__POLMATCH, NULL);
166	return (rc == -EACCES ? -ESRCH : rc);
167}
168
169/*
170 * LSM hook implementation that authorizes that a state matches
171 * the given policy, flow combo.
172 */
173int selinux_xfrm_state_pol_flow_match(struct xfrm_state *x,
174				      struct xfrm_policy *xp,
175				      const struct flowi_common *flic)
176{
177	u32 state_sid;
178	u32 flic_sid;
179
180	if (!xp->security)
181		if (x->security)
182			/* unlabeled policy and labeled SA can't match */
183			return 0;
184		else
185			/* unlabeled policy and unlabeled SA match all flows */
186			return 1;
187	else
188		if (!x->security)
189			/* unlabeled SA and labeled policy can't match */
190			return 0;
191		else
192			if (!selinux_authorizable_xfrm(x))
193				/* Not a SELinux-labeled SA */
194				return 0;
195
196	state_sid = x->security->ctx_sid;
197	flic_sid = flic->flowic_secid;
198
199	if (flic_sid != state_sid)
200		return 0;
201
202	/* We don't need a separate SA Vs. policy polmatch check since the SA
203	 * is now of the same label as the flow and a flow Vs. policy polmatch
204	 * check had already happened in selinux_xfrm_policy_lookup() above. */
205	return (avc_has_perm(flic_sid, state_sid,
206			     SECCLASS_ASSOCIATION, ASSOCIATION__SENDTO,
207			     NULL) ? 0 : 1);
208}
209
210static u32 selinux_xfrm_skb_sid_egress(struct sk_buff *skb)
211{
212	struct dst_entry *dst = skb_dst(skb);
213	struct xfrm_state *x;
214
215	if (dst == NULL)
216		return SECSID_NULL;
217	x = dst->xfrm;
218	if (x == NULL || !selinux_authorizable_xfrm(x))
219		return SECSID_NULL;
220
221	return x->security->ctx_sid;
222}
223
224static int selinux_xfrm_skb_sid_ingress(struct sk_buff *skb,
225					u32 *sid, int ckall)
226{
227	u32 sid_session = SECSID_NULL;
228	struct sec_path *sp = skb_sec_path(skb);
229
230	if (sp) {
231		int i;
232
233		for (i = sp->len - 1; i >= 0; i--) {
234			struct xfrm_state *x = sp->xvec[i];
235			if (selinux_authorizable_xfrm(x)) {
236				struct xfrm_sec_ctx *ctx = x->security;
237
238				if (sid_session == SECSID_NULL) {
239					sid_session = ctx->ctx_sid;
240					if (!ckall)
241						goto out;
242				} else if (sid_session != ctx->ctx_sid) {
243					*sid = SECSID_NULL;
244					return -EINVAL;
245				}
246			}
247		}
248	}
249
250out:
251	*sid = sid_session;
252	return 0;
253}
254
255/*
256 * LSM hook implementation that checks and/or returns the xfrm sid for the
257 * incoming packet.
258 */
259int selinux_xfrm_decode_session(struct sk_buff *skb, u32 *sid, int ckall)
260{
261	if (skb == NULL) {
262		*sid = SECSID_NULL;
263		return 0;
264	}
265	return selinux_xfrm_skb_sid_ingress(skb, sid, ckall);
266}
267
268int selinux_xfrm_skb_sid(struct sk_buff *skb, u32 *sid)
269{
270	int rc;
271
272	rc = selinux_xfrm_skb_sid_ingress(skb, sid, 0);
273	if (rc == 0 && *sid == SECSID_NULL)
274		*sid = selinux_xfrm_skb_sid_egress(skb);
275
276	return rc;
277}
278
279/*
280 * LSM hook implementation that allocs and transfers uctx spec to xfrm_policy.
281 */
282int selinux_xfrm_policy_alloc(struct xfrm_sec_ctx **ctxp,
283			      struct xfrm_user_sec_ctx *uctx,
284			      gfp_t gfp)
285{
286	return selinux_xfrm_alloc_user(ctxp, uctx, gfp);
287}
288
289/*
290 * LSM hook implementation that copies security data structure from old to new
291 * for policy cloning.
292 */
293int selinux_xfrm_policy_clone(struct xfrm_sec_ctx *old_ctx,
294			      struct xfrm_sec_ctx **new_ctxp)
295{
296	struct xfrm_sec_ctx *new_ctx;
297
298	if (!old_ctx)
299		return 0;
300
301	new_ctx = kmemdup(old_ctx, sizeof(*old_ctx) + old_ctx->ctx_len,
302			  GFP_ATOMIC);
303	if (!new_ctx)
304		return -ENOMEM;
305	atomic_inc(&selinux_xfrm_refcount);
306	*new_ctxp = new_ctx;
307
308	return 0;
309}
310
311/*
312 * LSM hook implementation that frees xfrm_sec_ctx security information.
313 */
314void selinux_xfrm_policy_free(struct xfrm_sec_ctx *ctx)
315{
316	selinux_xfrm_free(ctx);
317}
318
319/*
320 * LSM hook implementation that authorizes deletion of labeled policies.
321 */
322int selinux_xfrm_policy_delete(struct xfrm_sec_ctx *ctx)
323{
324	return selinux_xfrm_delete(ctx);
325}
326
327/*
328 * LSM hook implementation that allocates a xfrm_sec_state, populates it using
329 * the supplied security context, and assigns it to the xfrm_state.
330 */
331int selinux_xfrm_state_alloc(struct xfrm_state *x,
332			     struct xfrm_user_sec_ctx *uctx)
333{
334	return selinux_xfrm_alloc_user(&x->security, uctx, GFP_KERNEL);
335}
336
337/*
338 * LSM hook implementation that allocates a xfrm_sec_state and populates based
339 * on a secid.
340 */
341int selinux_xfrm_state_alloc_acquire(struct xfrm_state *x,
342				     struct xfrm_sec_ctx *polsec, u32 secid)
343{
344	int rc;
345	struct xfrm_sec_ctx *ctx;
346	char *ctx_str = NULL;
347	u32 str_len;
348
349	if (!polsec)
350		return 0;
351
352	if (secid == 0)
353		return -EINVAL;
354
355	rc = security_sid_to_context(secid, &ctx_str,
356				     &str_len);
357	if (rc)
358		return rc;
359
360	ctx = kmalloc(struct_size(ctx, ctx_str, 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);
374out:
375	kfree(ctx_str);
376	return rc;
377}
378
379/*
380 * LSM hook implementation that frees xfrm_state security information.
381 */
382void 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 */
390int 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 */
402int 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_sec_path(skb);
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 */
435int 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 = xfrm_dst_child(iter)) {
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