/*
   *  NSA 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.

   *
   *	This program is free software; you can redistribute it and/or modify
   *	it under the terms of the GNU General Public License version 2,
   *	as published by the Free Software Foundation.
   */
  
  /*
   * 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 = 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;
  	const struct task_security_struct *tsec = current_security();
  	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(sizeof(*ctx) + 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(tsec->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)
  {
  	const struct task_security_struct *tsec = current_security();
  
  	if (!ctx)
  		return 0;
  
  	return avc_has_perm(tsec->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, u8 dir)

  {

  	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 *fl)

  {
  	u32 state_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;

  	if (fl->flowi_secid != 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(fl->flowi_secid, 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->sp;

  	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;
  	int 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(sizeof(*ctx) + 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->sp;
  	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 = iter->child) {
  			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);

  }