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    IPsec: correct semantics for SELinux policy matching · 5b368e61
    由 Venkat Yekkirala 提交于 
    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: NVenkat Yekkirala <vyekkirala@TrustedCS.com>
Signed-off-by: NJames Morris <jmorris@namei.org>
    5b368e61
xfrm.h 2.2 KB
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/*
 * SELinux support for the XFRM LSM hooks
 *
 * Author : Trent Jaeger, <jaegert@us.ibm.com>
 * Updated : Venkat Yekkirala, <vyekkirala@TrustedCS.com>
 */
#ifndef _SELINUX_XFRM_H_
#define _SELINUX_XFRM_H_

int selinux_xfrm_policy_alloc(struct xfrm_policy *xp,
		struct xfrm_user_sec_ctx *sec_ctx, struct sock *sk);
int selinux_xfrm_policy_clone(struct xfrm_policy *old, struct xfrm_policy *new);
void selinux_xfrm_policy_free(struct xfrm_policy *xp);
int selinux_xfrm_policy_delete(struct xfrm_policy *xp);
int selinux_xfrm_state_alloc(struct xfrm_state *x,
	struct xfrm_user_sec_ctx *sec_ctx, struct xfrm_sec_ctx *pol, u32 secid);
void selinux_xfrm_state_free(struct xfrm_state *x);
int selinux_xfrm_state_delete(struct xfrm_state *x);
int selinux_xfrm_policy_lookup(struct xfrm_policy *xp, u32 fl_secid, u8 dir);
int selinux_xfrm_state_pol_flow_match(struct xfrm_state *x,
			struct xfrm_policy *xp, struct flowi *fl);
int selinux_xfrm_flow_state_match(struct flowi *fl, struct xfrm_state *xfrm,
			struct xfrm_policy *xp);


/*
 * Extract the security blob from the sock (it's actually on the socket)
 */
static inline struct inode_security_struct *get_sock_isec(struct sock *sk)
{
	if (!sk->sk_socket)
		return NULL;

	return SOCK_INODE(sk->sk_socket)->i_security;
}

#ifdef CONFIG_SECURITY_NETWORK_XFRM
int selinux_xfrm_sock_rcv_skb(u32 sid, struct sk_buff *skb,
			struct avc_audit_data *ad);
int selinux_xfrm_postroute_last(u32 isec_sid, struct sk_buff *skb,
			struct avc_audit_data *ad);
u32 selinux_socket_getpeer_stream(struct sock *sk);
u32 selinux_socket_getpeer_dgram(struct sk_buff *skb);
int selinux_xfrm_decode_session(struct sk_buff *skb, u32 *sid, int ckall);
#else
static inline int selinux_xfrm_sock_rcv_skb(u32 isec_sid, struct sk_buff *skb,
			struct avc_audit_data *ad)
{
	return 0;
}

static inline int selinux_xfrm_postroute_last(u32 isec_sid, struct sk_buff *skb,
			struct avc_audit_data *ad)
{
	return 0;
}

static inline int selinux_socket_getpeer_stream(struct sock *sk)
{
	return SECSID_NULL;
}

static inline int selinux_socket_getpeer_dgram(struct sk_buff *skb)
{
	return SECSID_NULL;
}
static inline int selinux_xfrm_decode_session(struct sk_buff *skb, u32 *sid, int ckall)
{
	*sid = SECSID_NULL;
	return 0;
}
#endif

#endif /* _SELINUX_XFRM_H_ */
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