security/selinux/xfrm.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 *  Security-Enhanced Linux (SELinux) security module
 *
 *  This file contains the SELinux XFRM hook function implementations.
 *
 *  Authors:  Serge Hallyn <sergeh@us.ibm.com>
 *	      Trent Jaeger <jaegert@us.ibm.com>
 *
 *  Updated: Venkat Yekkirala <vyekkirala@TrustedCS.com>
 *
 *           Granular IPSec Associations for use in MLS environments.
 *
 *  Copyright (C) 2005 International Business Machines Corporation
 *  Copyright (C) 2006 Trusted Computer Solutions, Inc.
 */

/*
 * USAGE:
 * NOTES:
 *   1. Make sure to enable the following options in your kernel config:
 *	CONFIG_SECURITY=y
 *	CONFIG_SECURITY_NETWORK=y
 *	CONFIG_SECURITY_NETWORK_XFRM=y
 *	CONFIG_SECURITY_SELINUX=m/y
 * ISSUES:
 *   1. Caching packets, so they are not dropped during negotiation
 *   2. Emulating a reasonable SO_PEERSEC across machines
 *   3. Testing addition of sk_policy's with security context via setsockopt
 */
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/security.h>
#include <linux/types.h>
#include <linux/slab.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/skbuff.h>
#include <linux/xfrm.h>
#include <net/xfrm.h>
#include <net/checksum.h>
#include <net/udp.h>
#include <linux/atomic.h>

#include "avc.h"
#include "objsec.h"
#include "xfrm.h"

/* Labeled XFRM instance counter */
atomic_t selinux_xfrm_refcount __read_mostly = ATOMIC_INIT(0);

/*
 * Returns true if the context is an LSM/SELinux context.
 */
static inline int selinux_authorizable_ctx(struct xfrm_sec_ctx *ctx)
{
	return (ctx &&
		(ctx->ctx_doi == XFRM_SC_DOI_LSM) &&
		(ctx->ctx_alg == XFRM_SC_ALG_SELINUX));
}

/*
 * Returns true if the xfrm contains a security blob for SELinux.
 */
static inline int selinux_authorizable_xfrm(struct xfrm_state *x)
{
	return selinux_authorizable_ctx(x->security);
}

/*
 * Allocates a xfrm_sec_state and populates it using the supplied security
 * xfrm_user_sec_ctx context.
 */
static int selinux_xfrm_alloc_user(struct xfrm_sec_ctx **ctxp,
				   struct xfrm_user_sec_ctx *uctx,
				   gfp_t gfp)
{
	int rc;
	struct xfrm_sec_ctx *ctx = NULL;
	u32 str_len;

	if (ctxp == NULL || uctx == NULL ||
	    uctx->ctx_doi != XFRM_SC_DOI_LSM ||
	    uctx->ctx_alg != XFRM_SC_ALG_SELINUX)
		return -EINVAL;

	str_len = uctx->ctx_len;
	if (str_len >= PAGE_SIZE)
		return -ENOMEM;

	ctx = kmalloc(struct_size(ctx, ctx_str, str_len + 1), gfp);
	if (!ctx)
		return -ENOMEM;

	ctx->ctx_doi = XFRM_SC_DOI_LSM;
	ctx->ctx_alg = XFRM_SC_ALG_SELINUX;
	ctx->ctx_len = str_len;
	memcpy(ctx->ctx_str, &uctx[1], str_len);
	ctx->ctx_str[str_len] = '\0';
	rc = security_context_to_sid(ctx->ctx_str, str_len,
				     &ctx->ctx_sid, gfp);
	if (rc)
		goto err;

	rc = avc_has_perm(current_sid(), ctx->ctx_sid,
			  SECCLASS_ASSOCIATION, ASSOCIATION__SETCONTEXT, NULL);
	if (rc)
		goto err;

	*ctxp = ctx;
	atomic_inc(&selinux_xfrm_refcount);
	return 0;

err:
	kfree(ctx);
	return rc;
}

/*
 * Free the xfrm_sec_ctx structure.
 */
static void selinux_xfrm_free(struct xfrm_sec_ctx *ctx)
{
	if (!ctx)
		return;

	atomic_dec(&selinux_xfrm_refcount);
	kfree(ctx);
}

/*
 * Authorize the deletion of a labeled SA or policy rule.
 */
static int selinux_xfrm_delete(struct xfrm_sec_ctx *ctx)
{
	if (!ctx)
		return 0;

	return avc_has_perm(current_sid(), ctx->ctx_sid,
			    SECCLASS_ASSOCIATION, ASSOCIATION__SETCONTEXT,
			    NULL);
}

/*
 * LSM hook implementation that authorizes that a flow can use a xfrm policy
 * rule.
 */
int selinux_xfrm_policy_lookup(struct xfrm_sec_ctx *ctx, u32 fl_secid)
{
	int rc;

	/* All flows should be treated as polmatch'ing an otherwise applicable
	 * "non-labeled" policy. This would prevent inadvertent "leaks". */
	if (!ctx)
		return 0;

	/* Context sid is either set to label or ANY_ASSOC */
	if (!selinux_authorizable_ctx(ctx))
		return -EINVAL;

	rc = avc_has_perm(fl_secid, ctx->ctx_sid,
			  SECCLASS_ASSOCIATION, ASSOCIATION__POLMATCH, NULL);
	return (rc == -EACCES ? -ESRCH : rc);
}

/*
 * LSM hook implementation that authorizes that a state matches
 * the given policy, flow combo.
 */
int selinux_xfrm_state_pol_flow_match(struct xfrm_state *x,
				      struct xfrm_policy *xp,
				      const struct flowi_common *flic)
{
	u32 state_sid;
	u32 flic_sid;

	if (!xp->security)
		if (x->security)
			/* unlabeled policy and labeled SA can't match */
			return 0;
		else
			/* unlabeled policy and unlabeled SA match all flows */
			return 1;
	else
		if (!x->security)
			/* unlabeled SA and labeled policy can't match */
			return 0;
		else
			if (!selinux_authorizable_xfrm(x))
				/* Not a SELinux-labeled SA */
				return 0;

	state_sid = x->security->ctx_sid;
	flic_sid = flic->flowic_secid;

	if (flic_sid != state_sid)
		return 0;

	/* We don't need a separate SA Vs. policy polmatch check since the SA
	 * is now of the same label as the flow and a flow Vs. policy polmatch
	 * check had already happened in selinux_xfrm_policy_lookup() above. */
	return (avc_has_perm(flic_sid, state_sid,
			     SECCLASS_ASSOCIATION, ASSOCIATION__SENDTO,
			     NULL) ? 0 : 1);
}

static u32 selinux_xfrm_skb_sid_egress(struct sk_buff *skb)
{
	struct dst_entry *dst = skb_dst(skb);
	struct xfrm_state *x;

	if (dst == NULL)
		return SECSID_NULL;
	x = dst->xfrm;
	if (x == NULL || !selinux_authorizable_xfrm(x))
		return SECSID_NULL;

	return x->security->ctx_sid;
}

static int selinux_xfrm_skb_sid_ingress(struct sk_buff *skb,
					u32 *sid, int ckall)
{
	u32 sid_session = SECSID_NULL;
	struct sec_path *sp = skb_sec_path(skb);

	if (sp) {
		int i;

		for (i = sp->len - 1; i >= 0; i--) {
			struct xfrm_state *x = sp->xvec[i];
			if (selinux_authorizable_xfrm(x)) {
				struct xfrm_sec_ctx *ctx = x->security;

				if (sid_session == SECSID_NULL) {
					sid_session = ctx->ctx_sid;
					if (!ckall)
						goto out;
				} else if (sid_session != ctx->ctx_sid) {
					*sid = SECSID_NULL;
					return -EINVAL;
				}
			}
		}
	}

out:
	*sid = sid_session;
	return 0;
}

/*
 * LSM hook implementation that checks and/or returns the xfrm sid for the
 * incoming packet.
 */
int selinux_xfrm_decode_session(struct sk_buff *skb, u32 *sid, int ckall)
{
	if (skb == NULL) {
		*sid = SECSID_NULL;
		return 0;
	}
	return selinux_xfrm_skb_sid_ingress(skb, sid, ckall);
}

int selinux_xfrm_skb_sid(struct sk_buff *skb, u32 *sid)
{
	int rc;

	rc = selinux_xfrm_skb_sid_ingress(skb, sid, 0);
	if (rc == 0 && *sid == SECSID_NULL)
		*sid = selinux_xfrm_skb_sid_egress(skb);

	return rc;
}

/*
 * LSM hook implementation that allocs and transfers uctx spec to xfrm_policy.
 */
int selinux_xfrm_policy_alloc(struct xfrm_sec_ctx **ctxp,
			      struct xfrm_user_sec_ctx *uctx,
			      gfp_t gfp)
{
	return selinux_xfrm_alloc_user(ctxp, uctx, gfp);
}

/*
 * LSM hook implementation that copies security data structure from old to new
 * for policy cloning.
 */
int selinux_xfrm_policy_clone(struct xfrm_sec_ctx *old_ctx,
			      struct xfrm_sec_ctx **new_ctxp)
{
	struct xfrm_sec_ctx *new_ctx;

	if (!old_ctx)
		return 0;

	new_ctx = kmemdup(old_ctx, sizeof(*old_ctx) + old_ctx->ctx_len,
			  GFP_ATOMIC);
	if (!new_ctx)
		return -ENOMEM;
	atomic_inc(&selinux_xfrm_refcount);
	*new_ctxp = new_ctx;

	return 0;
}

/*
 * LSM hook implementation that frees xfrm_sec_ctx security information.
 */
void selinux_xfrm_policy_free(struct xfrm_sec_ctx *ctx)
{
	selinux_xfrm_free(ctx);
}

/*
 * LSM hook implementation that authorizes deletion of labeled policies.
 */
int selinux_xfrm_policy_delete(struct xfrm_sec_ctx *ctx)
{
	return selinux_xfrm_delete(ctx);
}

/*
 * LSM hook implementation that allocates a xfrm_sec_state, populates it using
 * the supplied security context, and assigns it to the xfrm_state.
 */
int selinux_xfrm_state_alloc(struct xfrm_state *x,
			     struct xfrm_user_sec_ctx *uctx)
{
	return selinux_xfrm_alloc_user(&x->security, uctx, GFP_KERNEL);
}

/*
 * LSM hook implementation that allocates a xfrm_sec_state and populates based
 * on a secid.
 */
int selinux_xfrm_state_alloc_acquire(struct xfrm_state *x,
				     struct xfrm_sec_ctx *polsec, u32 secid)
{
	int rc;
	struct xfrm_sec_ctx *ctx;
	char *ctx_str = NULL;
	u32 str_len;

	if (!polsec)
		return 0;

	if (secid == 0)
		return -EINVAL;

	rc = security_sid_to_context(secid, &ctx_str,
				     &str_len);
	if (rc)
		return rc;

	ctx = kmalloc(struct_size(ctx, ctx_str, str_len), GFP_ATOMIC);
	if (!ctx) {
		rc = -ENOMEM;
		goto out;
	}

	ctx->ctx_doi = XFRM_SC_DOI_LSM;
	ctx->ctx_alg = XFRM_SC_ALG_SELINUX;
	ctx->ctx_sid = secid;
	ctx->ctx_len = str_len;
	memcpy(ctx->ctx_str, ctx_str, str_len);

	x->security = ctx;
	atomic_inc(&selinux_xfrm_refcount);
out:
	kfree(ctx_str);
	return rc;
}

/*
 * LSM hook implementation that frees xfrm_state security information.
 */
void selinux_xfrm_state_free(struct xfrm_state *x)
{
	selinux_xfrm_free(x->security);
}

/*
 * LSM hook implementation that authorizes deletion of labeled SAs.
 */
int selinux_xfrm_state_delete(struct xfrm_state *x)
{
	return selinux_xfrm_delete(x->security);
}

/*
 * LSM hook that controls access to unlabelled packets.  If
 * a xfrm_state is authorizable (defined by macro) then it was
 * already authorized by the IPSec process.  If not, then
 * we need to check for unlabelled access since this may not have
 * gone thru the IPSec process.
 */
int selinux_xfrm_sock_rcv_skb(u32 sk_sid, struct sk_buff *skb,
			      struct common_audit_data *ad)
{
	int i;
	struct sec_path *sp = skb_sec_path(skb);
	u32 peer_sid = SECINITSID_UNLABELED;

	if (sp) {
		for (i = 0; i < sp->len; i++) {
			struct xfrm_state *x = sp->xvec[i];

			if (x && selinux_authorizable_xfrm(x)) {
				struct xfrm_sec_ctx *ctx = x->security;
				peer_sid = ctx->ctx_sid;
				break;
			}
		}
	}

	/* This check even when there's no association involved is intended,
	 * according to Trent Jaeger, to make sure a process can't engage in
	 * non-IPsec communication unless explicitly allowed by policy. */
	return avc_has_perm(sk_sid, peer_sid,
			    SECCLASS_ASSOCIATION, ASSOCIATION__RECVFROM, ad);
}

/*
 * POSTROUTE_LAST hook's XFRM processing:
 * If we have no security association, then we need to determine
 * whether the socket is allowed to send to an unlabelled destination.
 * If we do have a authorizable security association, then it has already been
 * checked in the selinux_xfrm_state_pol_flow_match hook above.
 */
int selinux_xfrm_postroute_last(u32 sk_sid, struct sk_buff *skb,
				struct common_audit_data *ad, u8 proto)
{
	struct dst_entry *dst;

	switch (proto) {
	case IPPROTO_AH:
	case IPPROTO_ESP:
	case IPPROTO_COMP:
		/* We should have already seen this packet once before it
		 * underwent xfrm(s). No need to subject it to the unlabeled
		 * check. */
		return 0;
	default:
		break;
	}

	dst = skb_dst(skb);
	if (dst) {
		struct dst_entry *iter;

		for (iter = dst; iter != NULL; iter = xfrm_dst_child(iter)) {
			struct xfrm_state *x = iter->xfrm;

			if (x && selinux_authorizable_xfrm(x))
				return 0;
		}
	}

	/* This check even when there's no association involved is intended,
	 * according to Trent Jaeger, to make sure a process can't engage in
	 * non-IPsec communication unless explicitly allowed by policy. */
	return avc_has_perm(sk_sid, SECINITSID_UNLABELED,
			    SECCLASS_ASSOCIATION, ASSOCIATION__SENDTO, ad);
}