• Venkat Yekkirala's avatar
    IPsec: correct semantics for SELinux policy matching · 5b368e61
    Venkat Yekkirala authored
    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: default avatarVenkat Yekkirala <vyekkirala@TrustedCS.com>
    Signed-off-by: default avatarJames Morris <jmorris@namei.org>
    5b368e61
xfrm_user.c 49.4 KB