[PATCH] Permissive domain in userspace (Re: Some ideas in SE-PostgreSQL enhancement)

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KaiGai Kohei wrote:
> 4. Permissive domain in userspace
> 
> It is an issue got sleep for a few months.
>   http://marc.info/?l=selinux&m=122337314619667&w=2

It was discussed at the past a bit, but left it for several months.

Now we have a new idea of permissive domain which allows certain
domains to work as if being in permissive mode.
The in-kernel SELinux can handle it well, but userspace object
managers could not handler it because we don't have an interface
to tell what domain is permissive.

The attached patches are for the kernel and libselinux.

The kernel patch adds a flags field on av_decision, and returns
it as the sixth parameter on the reply of /selinux/access.

The libselinux patch enhance libselinux to understand it, and
two new interfaces are added.
 - security_compute_av_flags()
 - security_compute_av_flags_raw()
It also adds a new flags field on av_decision, but it is not
touched when we use the existing interfaces due to the binary
compatibility.

The standard userspace avc uses _flags interface, instead of
existing one, so it enables to control permissive domain.

IIRC, Eamon pointed out that it is preferable to put a new field
of 'permissive' than general purpose 'flags'. But it will require
interface changes, if we need more state in the future.
So, I don't change the implementation.

Please comment anything.

Thanks,
-- 
OSS Platform Development Division, NEC
KaiGai Kohei <kaigai@xxxxxxxxxxxxx>
 Signed-off-by: KaiGai Kohei <kaigai@xxxxxxxxxxxxx>
--
 libselinux/include/selinux/selinux.h |   15 ++++++
 libselinux/src/avc.c                 |   22 +++++---
 libselinux/src/compute_av.c          |   90 ++++++++++++++++++++++++++++------
 libselinux/src/selinux_internal.h    |    2 +
 4 files changed, 105 insertions(+), 24 deletions(-)

diff --git a/libselinux/include/selinux/selinux.h b/libselinux/include/selinux/selinux.h
index fab083e..7030f38 100644
--- a/libselinux/include/selinux/selinux.h
+++ b/libselinux/include/selinux/selinux.h
@@ -130,8 +130,12 @@ struct av_decision {
 	access_vector_t auditallow;
 	access_vector_t auditdeny;
 	unsigned int seqno;
+	unsigned int flags;
 };
 
+/* Definitions of av_decision.flags */
+#define SELINUX_AVD_FLAGS_PERMISSIVE	0x0001
+
 /* Structure for passing options, used by AVC and label subsystems */
 struct selinux_opt {
 	int type;
@@ -180,6 +184,17 @@ extern int security_compute_av_raw(security_context_t scon,
 				   access_vector_t requested,
 				   struct av_decision *avd);
 
+extern int security_compute_av_flags(security_context_t scon,
+				     security_context_t tcon,
+				     security_class_t tclass,
+				     access_vector_t requested,
+				     struct av_decision *avd);
+extern int security_compute_av_flags_raw(security_context_t scon,
+					 security_context_t tcon,
+					 security_class_t tclass,
+					 access_vector_t requested,
+					 struct av_decision *avd);
+
 /* Compute a labeling decision and set *newcon to refer to it.
    Caller must free via freecon. */
 extern int security_compute_create(security_context_t scon,
diff --git a/libselinux/src/avc.c b/libselinux/src/avc.c
index 1545dd3..f0e2d33 100644
--- a/libselinux/src/avc.c
+++ b/libselinux/src/avc.c
@@ -849,9 +849,9 @@ int avc_has_perm_noaudit(security_id_t ssid,
 				rc = -1;
 				goto out;
 			}
-			rc = security_compute_av_raw(ssid->ctx, tsid->ctx,
-						     tclass, requested,
-						     &entry.avd);
+			rc = security_compute_av_flags_raw(ssid->ctx, tsid->ctx,
+							   tclass, requested,
+							   &entry.avd);
 			if (rc)
 				goto out;
 			rc = avc_insert(ssid, tsid, tclass, &entry, aeref);
@@ -867,11 +867,13 @@ int avc_has_perm_noaudit(security_id_t ssid,
 	denied = requested & ~(ae->avd.allowed);
 
 	if (!requested || denied) {
-		if (avc_enforcing) {
+		if (!avc_enforcing ||
+		    (ae->avd.flags & SELINUX_AVD_FLAGS_PERMISSIVE))
+			ae->avd.allowed |= requested;
+		else {
 			errno = EACCES;
 			rc = -1;
-		} else
-			ae->avd.allowed |= requested;
+		}
 	}
 
       out:
@@ -885,9 +887,11 @@ int avc_has_perm(security_id_t ssid, security_id_t tsid,
 		 security_class_t tclass, access_vector_t requested,
 		 struct avc_entry_ref *aeref, void *auditdata)
 {
-	struct av_decision avd = { 0, 0, 0, 0, 0 };
+	struct av_decision avd;
 	int errsave, rc;
 
+	memset(&avd, 0, sizeof(avd));
+
 	rc = avc_has_perm_noaudit(ssid, tsid, tclass, requested, aeref, &avd);
 	errsave = errno;
 	avc_audit(ssid, tsid, tclass, requested, &avd, rc, auditdata);
@@ -917,8 +921,8 @@ int avc_compute_create(security_id_t ssid,  security_id_t tsid,
 	rc = avc_lookup(ssid, tsid, tclass, 0, &aeref);
 	if (rc) {
 		/* need to make a cache entry for this tuple */
-		rc = security_compute_av_raw(ssid->ctx, tsid->ctx,
-					     tclass, 0, &entry.avd);
+		rc = security_compute_av_flags_raw(ssid->ctx, tsid->ctx,
+						   tclass, 0, &entry.avd);
 		if (rc)
 			goto out;
 		rc = avc_insert(ssid, tsid, tclass, &entry, &aeref);
diff --git a/libselinux/src/compute_av.c b/libselinux/src/compute_av.c
index 45cd0db..a821d17 100644
--- a/libselinux/src/compute_av.c
+++ b/libselinux/src/compute_av.c
@@ -10,10 +10,11 @@
 #include "policy.h"
 #include "mapping.h"
 
-int security_compute_av_raw(security_context_t scon,
-			    security_context_t tcon,
-			    security_class_t tclass,
-			    access_vector_t requested, struct av_decision *avd)
+int security_compute_av_flags_raw(security_context_t scon,
+				  security_context_t tcon,
+				  security_class_t tclass,
+				  access_vector_t requested,
+				  struct av_decision *avd)
 {
 	char path[PATH_MAX];
 	char *buf;
@@ -49,12 +50,15 @@ int security_compute_av_raw(security_context_t scon,
 	if (ret < 0)
 		goto out2;
 
-	if (sscanf(buf, "%x %x %x %x %u", &avd->allowed,
-		   &avd->decided, &avd->auditallow, &avd->auditdeny,
-		   &avd->seqno) != 5) {
+	ret = sscanf(buf, "%x %x %x %x %u %x",
+		     &avd->allowed, &avd->decided,
+		     &avd->auditallow, &avd->auditdeny,
+		     &avd->seqno, &avd->flags);
+	if (ret < 5) {
 		ret = -1;
 		goto out2;
-	}
+	} else if (ret < 6)
+		avd->flags = 0;
 
 	map_decision(tclass, avd);
 
@@ -66,16 +70,44 @@ int security_compute_av_raw(security_context_t scon,
 	return ret;
 }
 
-hidden_def(security_compute_av_raw)
+hidden_def(security_compute_av_flags_raw)
 
-int security_compute_av(security_context_t scon,
-			security_context_t tcon,
-			security_class_t tclass,
-			access_vector_t requested, struct av_decision *avd)
+int security_compute_av_raw(security_context_t scon,
+			    security_context_t tcon,
+			    security_class_t tclass,
+			    access_vector_t requested,
+			    struct av_decision *avd)
 {
+	struct av_decision lavd;
 	int ret;
+
+	ret = security_compute_av_flags_raw(scon, tcon, tclass,
+					    requested, &lavd);
+	if (ret == 0) {
+		avd->allowed = lavd.allowed;
+		avd->decided = lavd.decided;
+		avd->auditallow = lavd.auditallow;
+		avd->auditdeny = lavd.auditdeny;
+		avd->seqno = lavd.seqno;
+		/* NOTE:
+		 * We should not return avd->flags via the interface
+		 * due to the binary compatibility.
+		 */
+	}
+	return ret;
+}
+
+hidden_def(security_compute_av_raw)
+
+int security_compute_av_flags(security_context_t scon,
+			      security_context_t tcon,
+			      security_class_t tclass,
+			      access_vector_t requested,
+			      struct av_decision *avd)
+{
 	security_context_t rscon = scon;
 	security_context_t rtcon = tcon;
+	int ret;
 
 	if (selinux_trans_to_raw_context(scon, &rscon))
 		return -1;
@@ -83,8 +115,8 @@ int security_compute_av(security_context_t scon,
 		freecon(rscon);
 		return -1;
 	}
-
-	ret = security_compute_av_raw(rscon, rtcon, tclass, requested, avd);
+	ret = security_compute_av_flags_raw(rscon, rtcon, tclass,
+					    requested, avd);
 
 	freecon(rscon);
 	freecon(rtcon);
@@ -92,4 +124,32 @@ int security_compute_av(security_context_t scon,
 	return ret;
 }
 
+hidden_def(security_compute_av_flags)
+
+int security_compute_av(security_context_t scon,
+			security_context_t tcon,
+			security_class_t tclass,
+			access_vector_t requested, struct av_decision *avd)
+{
+	struct av_decision lavd;
+	int ret;
+
+	ret = security_compute_av_flags(scon, tcon, tclass,
+					requested, &lavd);
+	if (ret == 0)
+	{
+		avd->allowed = lavd.allowed;
+		avd->decided = lavd.decided;
+		avd->auditallow = lavd.auditallow;
+		avd->auditdeny = lavd.auditdeny;
+		avd->seqno = lavd.seqno;
+		/* NOTE:
+		 * We should not return avd->flags via the interface
+		 * due to the binary compatibility.
+		 */
+	}
+
+	return ret;
+}
+
 hidden_def(security_compute_av)
diff --git a/libselinux/src/selinux_internal.h b/libselinux/src/selinux_internal.h
index 8b4c6d4..cfb18a5 100644
--- a/libselinux/src/selinux_internal.h
+++ b/libselinux/src/selinux_internal.h
@@ -16,6 +16,8 @@ hidden_proto(selinux_mkload_policy)
     hidden_proto(security_canonicalize_context_raw)
     hidden_proto(security_compute_av)
     hidden_proto(security_compute_av_raw)
+    hidden_proto(security_compute_av_flags)
+    hidden_proto(security_compute_av_flags_raw)
     hidden_proto(security_compute_user)
     hidden_proto(security_compute_user_raw)
     hidden_proto(security_compute_create)
 Signed-off-by: KaiGai Kohei <kaigai@xxxxxxxxxxxxx>
--
 security/selinux/avc.c              |    2 +-
 security/selinux/include/security.h |    4 +++-
 security/selinux/selinuxfs.c        |    4 ++--
 security/selinux/ss/services.c      |   30 +++++-------------------------
 4 files changed, 11 insertions(+), 29 deletions(-)

diff --git a/security/selinux/avc.c b/security/selinux/avc.c
index 7f9b5fa..b2ab608 100644
--- a/security/selinux/avc.c
+++ b/security/selinux/avc.c
@@ -927,7 +927,7 @@ int avc_has_perm_noaudit(u32 ssid, u32 tsid,
 	if (denied) {
 		if (flags & AVC_STRICT)
 			rc = -EACCES;
-		else if (!selinux_enforcing || security_permissive_sid(ssid))
+		else if (!selinux_enforcing || (avd->flags & AVD_FLAGS_PERMISSIVE))
 			avc_update_node(AVC_CALLBACK_GRANT, requested, ssid,
 					tsid, tclass, avd->seqno);
 		else
diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h
index 5c3434f..a7be3f0 100644
--- a/security/selinux/include/security.h
+++ b/security/selinux/include/security.h
@@ -91,9 +91,11 @@ struct av_decision {
 	u32 auditallow;
 	u32 auditdeny;
 	u32 seqno;
+	u32 flags;
 };
 
-int security_permissive_sid(u32 sid);
+/* definitions of av_decision.flags */
+#define AVD_FLAGS_PERMISSIVE	0x0001
 
 int security_compute_av(u32 ssid, u32 tsid,
 	u16 tclass, u32 requested,
diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
index d3c8b98..4d56ab1 100644
--- a/security/selinux/selinuxfs.c
+++ b/security/selinux/selinuxfs.c
@@ -594,10 +594,10 @@ static ssize_t sel_write_access(struct file *file, char *buf, size_t size)
 		goto out2;
 
 	length = scnprintf(buf, SIMPLE_TRANSACTION_LIMIT,
-			  "%x %x %x %x %u",
+			  "%x %x %x %x %u %x",
 			  avd.allowed, 0xffffffff,
 			  avd.auditallow, avd.auditdeny,
-			  avd.seqno);
+			  avd.seqno, avd.flags);
 out2:
 	kfree(tcon);
 out:
diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index deeec6c..500e6f7 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -410,6 +410,7 @@ static int context_struct_compute_av(struct context *scontext,
 	avd->auditallow = 0;
 	avd->auditdeny = 0xffffffff;
 	avd->seqno = latest_granting;
+	avd->flags = 0;
 
 	/*
 	 * Check for all the invalid cases.
@@ -528,31 +529,6 @@ inval_class:
 	return 0;
 }
 
-/*
- * Given a sid find if the type has the permissive flag set
- */
-int security_permissive_sid(u32 sid)
-{
-	struct context *context;
-	u32 type;
-	int rc;
-
-	read_lock(&policy_rwlock);
-
-	context = sidtab_search(&sidtab, sid);
-	BUG_ON(!context);
-
-	type = context->type;
-	/*
-	 * we are intentionally using type here, not type-1, the 0th bit may
-	 * someday indicate that we are globally setting permissive in policy.
-	 */
-	rc = ebitmap_get_bit(&policydb.permissive_map, type);
-
-	read_unlock(&policy_rwlock);
-	return rc;
-}
-
 static int security_validtrans_handle_fail(struct context *ocontext,
 					   struct context *ncontext,
 					   struct context *tcontext,
@@ -767,6 +743,10 @@ int security_compute_av(u32 ssid,
 
 	rc = context_struct_compute_av(scontext, tcontext, tclass,
 				       requested, avd);
+
+	/* permissive domain? */
+	if (ebitmap_get_bit(&policydb.permissive_map, scontext->type))
+	    avd->flags |= AVD_FLAGS_PERMISSIVE;
 out:
 	read_unlock(&policy_rwlock);
 	return rc;

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