kernel-ark/security/selinux/xfrm.c
Venkat Yekkirala 5b368e61c2 IPsec: correct semantics for SELinux policy matching
Currently when an IPSec policy rule doesn't specify a security
context, it is assumed to be "unlabeled" by SELinux, and so
the IPSec policy rule fails to match to a flow that it would
otherwise match to, unless one has explicitly added an SELinux
policy rule allowing the flow to "polmatch" to the "unlabeled"
IPSec policy rules. In the absence of such an explicitly added
SELinux policy rule, the IPSec policy rule fails to match and
so the packet(s) flow in clear text without the otherwise applicable
xfrm(s) applied.

The above SELinux behavior violates the SELinux security notion of
"deny by default" which should actually translate to "encrypt by
default" in the above case.

This was first reported by Evgeniy Polyakov and the way James Morris
was seeing the problem was when connecting via IPsec to a
confined service on an SELinux box (vsftpd), which did not have the
appropriate SELinux policy permissions to send packets via IPsec.

With this patch applied, SELinux "polmatching" of flows Vs. IPSec
policy rules will only come into play when there's a explicit context
specified for the IPSec policy rule (which also means there's corresponding
SELinux policy allowing appropriate domains/flows to polmatch to this context).

Secondly, when a security module is loaded (in this case, SELinux), the
security_xfrm_policy_lookup() hook can return errors other than access denied,
such as -EINVAL.  We were not handling that correctly, and in fact
inverting the return logic and propagating a false "ok" back up to
xfrm_lookup(), which then allowed packets to pass as if they were not
associated with an xfrm policy.

The solution for this is to first ensure that errno values are
correctly propagated all the way back up through the various call chains
from security_xfrm_policy_lookup(), and handled correctly.

Then, flow_cache_lookup() is modified, so that if the policy resolver
fails (typically a permission denied via the security module), the flow
cache entry is killed rather than having a null policy assigned (which
indicates that the packet can pass freely).  This also forces any future
lookups for the same flow to consult the security module (e.g. SELinux)
for current security policy (rather than, say, caching the error on the
flow cache entry).

This patch: Fix the selinux side of things.

This makes sure SELinux polmatching of flow contexts to IPSec policy
rules comes into play only when an explicit context is associated
with the IPSec policy rule.

Also, this no longer defaults the context of a socket policy to
the context of the socket since the "no explicit context" case
is now handled properly.

Signed-off-by: Venkat Yekkirala <vyekkirala@TrustedCS.com>
Signed-off-by: James Morris <jmorris@namei.org>
2006-10-11 23:59:37 -07:00

573 lines
12 KiB
C

/*
* 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/module.h>
#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/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 <asm/semaphore.h>
#include "avc.h"
#include "objsec.h"
#include "xfrm.h"
/*
* 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_policy *xp, u32 fl_secid, u8 dir)
{
int rc;
u32 sel_sid;
struct xfrm_sec_ctx *ctx;
/* Context sid is either set to label or ANY_ASSOC */
if ((ctx = xp->security)) {
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)
rc = -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,
struct flowi *fl)
{
u32 state_sid;
u32 pol_sid;
int err;
if (xp->security) {
if (!x->security)
/* unlabeled SA and labeled policy can't match */
return 0;
else
state_sid = x->security->ctx_sid;
pol_sid = xp->security->ctx_sid;
} else
if (x->security)
/* unlabeled policy and labeled SA can't match */
return 0;
else
/* unlabeled policy and unlabeled SA match all flows */
return 1;
err = avc_has_perm(state_sid, pol_sid, SECCLASS_ASSOCIATION,
ASSOCIATION__POLMATCH,
NULL);
if (err)
return 0;
err = avc_has_perm(fl->secid, state_sid, SECCLASS_ASSOCIATION,
ASSOCIATION__SENDTO,
NULL)? 0:1;
return err;
}
/*
* LSM hook implementation that authorizes that a particular outgoing flow
* can use a given security association.
*/
int selinux_xfrm_flow_state_match(struct flowi *fl, struct xfrm_state *xfrm,
struct xfrm_policy *xp)
{
int rc = 0;
u32 sel_sid = SECINITSID_UNLABELED;
struct xfrm_sec_ctx *ctx;
if (!xp->security)
if (!xfrm->security)
return 1;
else
return 0;
else
if (!xfrm->security)
return 0;
/* Context sid is either set to label or ANY_ASSOC */
if ((ctx = xfrm->security)) {
if (!selinux_authorizable_ctx(ctx))
return 0;
sel_sid = ctx->ctx_sid;
}
rc = avc_has_perm(fl->secid, sel_sid, SECCLASS_ASSOCIATION,
ASSOCIATION__SENDTO,
NULL)? 0:1;
return rc;
}
/*
* LSM hook implementation that determines the sid for the session.
*/
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, struct xfrm_sec_ctx *pol, u32 sid)
{
int rc = 0;
struct task_security_struct *tsec = current->security;
struct xfrm_sec_ctx *ctx = NULL;
char *ctx_str = NULL;
u32 str_len;
u32 ctx_sid;
BUG_ON(uctx && pol);
if (!uctx)
goto not_from_user;
if (uctx->ctx_doi != XFRM_SC_ALG_SELINUX)
return -EINVAL;
if (uctx->ctx_len >= PAGE_SIZE)
return -ENOMEM;
*ctxp = ctx = kmalloc(sizeof(*ctx) +
uctx->ctx_len,
GFP_KERNEL);
if (!ctx)
return -ENOMEM;
ctx->ctx_doi = uctx->ctx_doi;
ctx->ctx_len = uctx->ctx_len;
ctx->ctx_alg = uctx->ctx_alg;
memcpy(ctx->ctx_str,
uctx+1,
ctx->ctx_len);
rc = security_context_to_sid(ctx->ctx_str,
ctx->ctx_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:
if (pol) {
rc = security_sid_mls_copy(pol->ctx_sid, sid, &ctx_sid);
if (rc)
goto out;
}
else
ctx_sid = sid;
rc = security_sid_to_context(ctx_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 = ctx_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_policy *xp,
struct xfrm_user_sec_ctx *uctx, struct sock *sk)
{
int err;
u32 sid;
BUG_ON(!xp);
BUG_ON(uctx && sk);
if (sk) {
struct sk_security_struct *ssec = sk->sk_security;
sid = ssec->sid;
}
else
sid = SECSID_NULL;
err = selinux_xfrm_sec_ctx_alloc(&xp->security, uctx, NULL, sid);
return err;
}
/*
* LSM hook implementation that copies security data structure from old to
* new for policy cloning.
*/
int selinux_xfrm_policy_clone(struct xfrm_policy *old, struct xfrm_policy *new)
{
struct xfrm_sec_ctx *old_ctx, *new_ctx;
old_ctx = old->security;
if (old_ctx) {
new_ctx = new->security = kmalloc(sizeof(*new_ctx) +
old_ctx->ctx_len,
GFP_KERNEL);
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);
}
return 0;
}
/*
* LSM hook implementation that frees xfrm_policy security information.
*/
void selinux_xfrm_policy_free(struct xfrm_policy *xp)
{
struct xfrm_sec_ctx *ctx = xp->security;
if (ctx)
kfree(ctx);
}
/*
* LSM hook implementation that authorizes deletion of labeled policies.
*/
int selinux_xfrm_policy_delete(struct xfrm_policy *xp)
{
struct task_security_struct *tsec = current->security;
struct xfrm_sec_ctx *ctx = xp->security;
int rc = 0;
if (ctx)
rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
SECCLASS_ASSOCIATION,
ASSOCIATION__SETCONTEXT, NULL);
return rc;
}
/*
* 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,
struct xfrm_sec_ctx *pol, u32 secid)
{
int err;
BUG_ON(!x);
err = selinux_xfrm_sec_ctx_alloc(&x->security, uctx, pol, secid);
return err;
}
/*
* LSM hook implementation that frees xfrm_state security information.
*/
void selinux_xfrm_state_free(struct xfrm_state *x)
{
struct xfrm_sec_ctx *ctx = x->security;
if (ctx)
kfree(ctx);
}
/*
* SELinux internal function to retrieve the context of a connected
* (sk->sk_state == TCP_ESTABLISHED) TCP socket based on its security
* association used to connect to the remote socket.
*
* Retrieve via getsockopt SO_PEERSEC.
*/
u32 selinux_socket_getpeer_stream(struct sock *sk)
{
struct dst_entry *dst, *dst_test;
u32 peer_sid = SECSID_NULL;
if (sk->sk_state != TCP_ESTABLISHED)
goto out;
dst = sk_dst_get(sk);
if (!dst)
goto out;
for (dst_test = dst; dst_test != 0;
dst_test = dst_test->child) {
struct xfrm_state *x = dst_test->xfrm;
if (x && selinux_authorizable_xfrm(x)) {
struct xfrm_sec_ctx *ctx = x->security;
peer_sid = ctx->ctx_sid;
break;
}
}
dst_release(dst);
out:
return peer_sid;
}
/*
* SELinux internal function to retrieve the context of a UDP packet
* based on its security association used to connect to the remote socket.
*
* Retrieve via setsockopt IP_PASSSEC and recvmsg with control message
* type SCM_SECURITY.
*/
u32 selinux_socket_getpeer_dgram(struct sk_buff *skb)
{
struct sec_path *sp;
if (skb == NULL)
return SECSID_NULL;
if (skb->sk->sk_protocol != IPPROTO_UDP)
return SECSID_NULL;
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;
return ctx->ctx_sid;
}
}
}
return SECSID_NULL;
}
/*
* LSM hook implementation that authorizes deletion of labeled SAs.
*/
int selinux_xfrm_state_delete(struct xfrm_state *x)
{
struct task_security_struct *tsec = current->security;
struct xfrm_sec_ctx *ctx = x->security;
int rc = 0;
if (ctx)
rc = avc_has_perm(tsec->sid, ctx->ctx_sid,
SECCLASS_ASSOCIATION,
ASSOCIATION__SETCONTEXT, NULL);
return rc;
}
/*
* 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 avc_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;
}
}
}
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 xfrm_policy_lookup hook.
*/
int selinux_xfrm_postroute_last(u32 isec_sid, struct sk_buff *skb,
struct avc_audit_data *ad)
{
struct dst_entry *dst;
int rc = 0;
dst = skb->dst;
if (dst) {
struct dst_entry *dst_test;
for (dst_test = dst; dst_test != 0;
dst_test = dst_test->child) {
struct xfrm_state *x = dst_test->xfrm;
if (x && selinux_authorizable_xfrm(x))
goto out;
}
}
rc = avc_has_perm(isec_sid, SECINITSID_UNLABELED, SECCLASS_ASSOCIATION,
ASSOCIATION__SENDTO, ad);
out:
return rc;
}