On Tue, 2017-10-31 at 09:43 -0400, Stephen Smalley wrote:

On Tue, 2017-10-31 at 12:11 +0100, Florian Westphal wrote:

quoted

Stephen Smalley [off-list ref] wrote:

quoted

Since 4.14-rc1, the selinux-testsuite has been encountering
sporadic
failures during testing of labeled IPSEC. git bisect pointed to
commit ec30d78c14a813db39a647b6a348b4286 ("xfrm: add xdst pcpu
cache").
The xdst pcpu cache is only checking that the policies are the
same,
but does not validate that the policy, state, and flow match with
respect
to security context labeling.??As a result, the wrong SA could be
used
and the receiver could end up performing permission checking and
providing SO_PEERSEC or SCM_SECURITY values for the wrong
security
context.
security_xfrm_state_pol_flow_match() exists for this purpose and
is
already called from xfrm_state_look_at() for matching purposes.
Further, xfrm_state_look_at() also performs a
xfrm_selector_match()
test,
which is also missing from the xdst pcpu cache logic.??Add calls
to
both
of these functions when validating the cache entry.??With these
changes,
the selinux-testsuite passes all tests again.

Fixes: ec30d78c14a813db39a647b6a348b4286ba4abf5 ("xfrm: add xdst
pcpu cache")
Signed-off-by: Stephen Smalley <redacted>
---
This is an RFC because I am not entirely confident in the fix,
e.g.
is it
sufficient to perform this matching only on the first xfrm or do
they all
need to be walked as in xfrm_bundle_ok()???Also, should we
perform
this
matching before (as in this patch) or after calling
xfrm_bundle_ok()? Also,
do we need to test xfrm->sel.family before calling
xfrm_selector_match
(as in this patch) or not - xfrm_state_look_at() does so when the
state is XFRM_STATE_VALID but not when it is _ERROR or _EXPIRED?

No idea.

I looked at the old flow cache but i don't see any of these extra
checks there either.

However, old flow cache stored flowi struct as key, and that
contains
a
flowi_secid,??populated by the decode_session hooks.

Was it enough to check for identical flowi_secid in the flowi
structs
to
avoid this problem or am i missing something?

I'm not sure, but security_xfrm_state_pol_flow_match() ->
selinux_xfrm_state_pol_flow_match() does more than just compare flow
secids.

Also, there is the separate issue of the missing
xfrm_selector_match()
call, which can also cause the wrong SA to be used independent of
anything LSM/SELinux-related.

It is a regression; the correct SA was being used prior to the xdst
pcpu cache commit.??Reproducible using the selinux-testsuite, most
easily run on a Fedora VM,
git clone https://github.com/SELinuxProject/selinux-testsuite/
sudo dnf install perl-Test perl-Test-Harness perl-Test-Simple
selinux-policy-devel gcc libselinux-devel net-tools netlabel_tools
iptables

Actually, you should just run 'sudo make test' instead of the
individual commands below.  I was breaking out the individual commands
to avoid running the rest of the testsuite unrelated to networking, but
 that won't pick up all of the dependencies the first time.  Sorry.

sudo make -C policy load
cd tests/inet_socket
while sudo ./test; do : ; done

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