// 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_flex(*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 + 1;
        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_flex(*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);
}