security,lockdown,selinux: implement SELinux lockdown

Implement a SELinux hook for lockdown.  If the lockdown module is also
enabled, then a denial by the lockdown module will take precedence over
SELinux, so SELinux can only further restrict lockdown decisions.
The SELinux hook only distinguishes at the granularity of integrity
versus confidentiality similar to the lockdown module, but includes the
full lockdown reason as part of the audit record as a hint in diagnosing
what triggered the denial.  To support this auditing, move the
lockdown_reasons[] string array from being private to the lockdown
module to the security framework so that it can be used by the lsm audit
code and so that it is always available even when the lockdown module
is disabled.

Note that the SELinux implementation allows the integrity and
confidentiality reasons to be controlled independently from one another.
Thus, in an SELinux policy, one could allow operations that specify
an integrity reason while blocking operations that specify a
confidentiality reason. The SELinux hook implementation is
stricter than the lockdown module in validating the provided reason value.

Sample AVC audit output from denials:
avc:  denied  { integrity } for pid=3402 comm="fwupd"
 lockdown_reason="/dev/mem,kmem,port" scontext=system_u:system_r:fwupd_t:s0
 tcontext=system_u:system_r:fwupd_t:s0 tclass=lockdown permissive=0

avc:  denied  { confidentiality } for pid=4628 comm="cp"
 lockdown_reason="/proc/kcore access"
 scontext=unconfined_u:unconfined_r:test_lockdown_integrity_t:s0-s0:c0.c1023
 tcontext=unconfined_u:unconfined_r:test_lockdown_integrity_t:s0-s0:c0.c1023
 tclass=lockdown permissive=0

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Reviewed-by: James Morris <jamorris@linux.microsoft.com>
[PM: some merge fuzz do the the perf hooks]
Signed-off-by: Paul Moore <paul@paul-moore.com>

1 files changed, 30 insertions, 0 deletions

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 116b4d644f68..9e1c4780dc20 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -6795,6 +6795,34 @@ static void selinux_bpf_prog_free(struct bpf_prog_aux *aux)
 }
 #endif
 
+static int selinux_lockdown(enum lockdown_reason what)
+{
+	struct common_audit_data ad;
+	u32 sid = current_sid();
+	int invalid_reason = (what <= LOCKDOWN_NONE) ||
+			     (what == LOCKDOWN_INTEGRITY_MAX) ||
+			     (what >= LOCKDOWN_CONFIDENTIALITY_MAX);
+
+	if (WARN(invalid_reason, "Invalid lockdown reason")) {
+		audit_log(audit_context(),
+			  GFP_ATOMIC, AUDIT_SELINUX_ERR,
+			  "lockdown_reason=invalid");
+		return -EINVAL;
+	}
+
+	ad.type = LSM_AUDIT_DATA_LOCKDOWN;
+	ad.u.reason = what;
+
+	if (what <= LOCKDOWN_INTEGRITY_MAX)
+		return avc_has_perm(&selinux_state,
+				    sid, sid, SECCLASS_LOCKDOWN,
+				    LOCKDOWN__INTEGRITY, &ad);
+	else
+		return avc_has_perm(&selinux_state,
+				    sid, sid, SECCLASS_LOCKDOWN,
+				    LOCKDOWN__CONFIDENTIALITY, &ad);
+}
+
 struct lsm_blob_sizes selinux_blob_sizes __lsm_ro_after_init = {
 	.lbs_cred = sizeof(struct task_security_struct),
 	.lbs_file = sizeof(struct file_security_struct),
@@ -7107,6 +7135,8 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(perf_event_read, selinux_perf_event_read),
 	LSM_HOOK_INIT(perf_event_write, selinux_perf_event_write),
 #endif
+
+	LSM_HOOK_INIT(locked_down, selinux_lockdown),
 };
 
 static __init int selinux_init(void)