/*
 *  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/netfilter.h>
#include <linux/netfilter_ipv4.h>
#include <linux/netfilter_ipv6.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 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);
}

/*
 * 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;
        u32 sel_sid;

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

                sel_sid = ctx->ctx_sid;
        } else
                /*
                 * All flows should be treated as polmatch'ing an
                 * otherwise applicable "non-labeled" policy. This
                 * would prevent inadvertent "leaks".
                 */
                return 0;

        rc = avc_has_perm(fl_secid, sel_sid, SECCLASS_ASSOCIATION,
                          ASSOCIATION__POLMATCH,
                          NULL);

        if (rc == -EACCES)
                return -ESRCH;

        return 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;
        int rc;

        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;

        rc = avc_has_perm(fl->flowi_secid, state_sid, SECCLASS_ASSOCIATION,
                          ASSOCIATION__SENDTO,
                          NULL)? 0:1;

        /*
         * 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 rc;
}

/*
 * 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)
{
        struct sec_path *sp;

        *sid = SECSID_NULL;

        if (skb == NULL)
                return 0;

        sp = skb->sp;
        if (sp) {
                int i, sid_set = 0;

                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_set) {
                                        *sid = ctx->ctx_sid;
                                        sid_set = 1;

                                        if (!ckall)
                                                break;
                                } else if (*sid != ctx->ctx_sid)
                                        return -EINVAL;
                        }
                }
        }

        return 0;
}

/*
 * Security blob allocation for xfrm_policy and xfrm_state
 * CTX does not have a meaningful value on input
 */
static int selinux_xfrm_sec_ctx_alloc(struct xfrm_sec_ctx **ctxp,
        struct xfrm_user_sec_ctx *uctx, u32 sid)
{
        int rc = 0;
        const struct task_security_struct *tsec = current_security();
        struct xfrm_sec_ctx *ctx = NULL;
        char *ctx_str = NULL;
        u32 str_len;

        BUG_ON(uctx && sid);

        if (!uctx)
                goto not_from_user;

        if (uctx->ctx_alg != XFRM_SC_ALG_SELINUX)
                return -EINVAL;

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

        *ctxp = ctx = kmalloc(sizeof(*ctx) +
                              str_len + 1,
                              GFP_KERNEL);

        if (!ctx)
                return -ENOMEM;

        ctx->ctx_doi = uctx->ctx_doi;
        ctx->ctx_len = str_len;
        ctx->ctx_alg = uctx->ctx_alg;

        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);

        if (rc)
                goto out;

        /*
         * Does the subject have permission to set security context?
         */
        rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
                          SECCLASS_ASSOCIATION,
                          ASSOCIATION__SETCONTEXT, NULL);
        if (rc)
                goto out;

        return rc;

not_from_user:
        rc = security_sid_to_context(sid, &ctx_str, &str_len);
        if (rc)
                goto out;

        *ctxp = 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 = sid;
        ctx->ctx_len = str_len;
        memcpy(ctx->ctx_str,
               ctx_str,
               str_len);

        goto out2;

out:
        *ctxp = NULL;
        kfree(ctx);
out2:
        kfree(ctx_str);
        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)
{
        int err;

        BUG_ON(!uctx);

        err = selinux_xfrm_sec_ctx_alloc(ctxp, uctx, 0);
        if (err == 0)
                atomic_inc(&selinux_xfrm_refcount);

        return err;
}


/*
 * 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) {
                new_ctx = kmalloc(sizeof(*old_ctx) + old_ctx->ctx_len,
                                  GFP_ATOMIC);
                if (!new_ctx)
                        return -ENOMEM;

                memcpy(new_ctx, old_ctx, sizeof(*new_ctx));
                memcpy(new_ctx->ctx_str, old_ctx->ctx_str, new_ctx->ctx_len);
                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)
{
        atomic_dec(&selinux_xfrm_refcount);
        kfree(ctx);
}

/*
 * LSM hook implementation that authorizes deletion of labeled policies.
 */
int selinux_xfrm_policy_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 allocs and transfers sec_ctx spec to
 * xfrm_state.
 */
int selinux_xfrm_state_alloc(struct xfrm_state *x, struct xfrm_user_sec_ctx *uctx,
                u32 secid)
{
        int err;

        BUG_ON(!x);

        err = selinux_xfrm_sec_ctx_alloc(&x->security, uctx, secid);
        if (err == 0)
                atomic_inc(&selinux_xfrm_refcount);
        return err;
}

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

 /*
  * LSM hook implementation that authorizes deletion of labeled SAs.
  */
int selinux_xfrm_state_delete(struct xfrm_state *x)
{
        const struct task_security_struct *tsec = current_security();
        struct xfrm_sec_ctx *ctx = x->security;

        if (!ctx)
                return 0;

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

/*
 * 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 isec_sid, struct sk_buff *skb,
                                struct common_audit_data *ad)
{
        int i, rc = 0;
        struct sec_path *sp;
        u32 sel_sid = SECINITSID_UNLABELED;

        sp = skb->sp;

        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;
                                sel_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.
         */

        rc = avc_has_perm(isec_sid, sel_sid, SECCLASS_ASSOCIATION,
                          ASSOCIATION__RECVFROM, ad);

        return rc;
}

/*
 * 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 isec_sid, struct sk_buff *skb,
                                        struct common_audit_data *ad, u8 proto)
{
        struct dst_entry *dst;
        int rc = 0;

        dst = skb_dst(skb);

        if (dst) {
                struct dst_entry *dst_test;

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

                        if (x && selinux_authorizable_xfrm(x))
                                goto out;
                }
        }

        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.
                 */
                goto out;
        default:
                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.
         */

        rc = avc_has_perm(isec_sid, SECINITSID_UNLABELED, SECCLASS_ASSOCIATION,
                          ASSOCIATION__SENDTO, ad);
out:
        return rc;
}