selinux: add type_transition with name extension support for selinuxfs

The attached patch allows /selinux/create takes optional 4th argument
to support TYPE_TRANSITION with name extension for userspace object
managers.
If 4th argument is not supplied, it shall perform as existing kernel.
In fact, the regression test of SE-PostgreSQL works well on the patched
kernel.

Thanks,
Signed-off-by: KaiGai Kohei <kohei.kaigai@eu.nec.com>
[manually verify fuzz was not an issue, and it wasn't: eparis]
Signed-off-by: Eric Paris <eparis@redhat.com>

security/selinux/include/security.h

@@ -112,8 +112,8 @@ void security_compute_av_user(u32 ssid, u32 tsid,
 int security_transition_sid(u32 ssid, u32 tsid, u16 tclass,
 			    const struct qstr *qstr, u32 *out_sid);
 
-int security_transition_sid_user(u32 ssid, u32 tsid,
-				 u16 tclass, u32 *out_sid);
+int security_transition_sid_user(u32 ssid, u32 tsid, u16 tclass,
+				 const char *objname, u32 *out_sid);
 
 int security_member_sid(u32 ssid, u32 tsid,
 	u16 tclass, u32 *out_sid);

security/selinux/selinuxfs.c

@@ -753,11 +753,13 @@ static ssize_t sel_write_access(struct file *file, char *buf, size_t size)
 static ssize_t sel_write_create(struct file *file, char *buf, size_t size)
 {
 	char *scon = NULL, *tcon = NULL;
+	char *namebuf = NULL, *objname = NULL;
 	u32 ssid, tsid, newsid;
 	u16 tclass;
 	ssize_t length;
 	char *newcon = NULL;
 	u32 len;
+	int nargs;
 
 	length = task_has_security(current, SECURITY__COMPUTE_CREATE);
 	if (length)
@@ -773,9 +775,17 @@ static ssize_t sel_write_create(struct file *file, char *buf, size_t size)
 	if (!tcon)
 		goto out;
 
+	length = -ENOMEM;
+	namebuf = kzalloc(size + 1, GFP_KERNEL);
+	if (!namebuf)
+		goto out;
+
 	length = -EINVAL;
-	if (sscanf(buf, "%s %s %hu", scon, tcon, &tclass) != 3)
+	nargs = sscanf(buf, "%s %s %hu %s", scon, tcon, &tclass, namebuf);
+	if (nargs < 3 || nargs > 4)
 		goto out;
+	if (nargs == 4)
+		objname = namebuf;
 
 	length = security_context_to_sid(scon, strlen(scon) + 1, &ssid);
 	if (length)
@@ -785,7 +795,8 @@ static ssize_t sel_write_create(struct file *file, char *buf, size_t size)
 	if (length)
 		goto out;
 
-	length = security_transition_sid_user(ssid, tsid, tclass, &newsid);
+	length = security_transition_sid_user(ssid, tsid, tclass,
+					      objname, &newsid);
 	if (length)
 		goto out;
 
@@ -804,6 +815,7 @@ static ssize_t sel_write_create(struct file *file, char *buf, size_t size)
 	length = len;
 out:
 	kfree(newcon);
+	kfree(namebuf);
 	kfree(tcon);
 	kfree(scon);
 	return length;

security/selinux/ss/services.c

@@ -1360,14 +1360,14 @@ static int compute_sid_handle_invalid_context(
 
 static void filename_compute_type(struct policydb *p, struct context *newcontext,
 				  u32 scon, u32 tcon, u16 tclass,
-				  const struct qstr *qstr)
+				  const char *objname)
 {
 	struct filename_trans *ft;
 	for (ft = p->filename_trans; ft; ft = ft->next) {
 		if (ft->stype == scon &&
 		    ft->ttype == tcon &&
 		    ft->tclass == tclass &&
-		    !strcmp(ft->name, qstr->name)) {
+		    !strcmp(ft->name, objname)) {
 			newcontext->type = ft->otype;
 			return;
 		}
@@ -1378,7 +1378,7 @@ static int security_compute_sid(u32 ssid,
 				u32 tsid,
 				u16 orig_tclass,
 				u32 specified,
-				const struct qstr *qstr,
+				const char *objname,
 				u32 *out_sid,
 				bool kern)
 {
@@ -1479,9 +1479,9 @@ static int security_compute_sid(u32 ssid,
 	}
 
 	/* if we have a qstr this is a file trans check so check those rules */
-	if (qstr)
+	if (objname)
 		filename_compute_type(&policydb, &newcontext, scontext->type,
-				      tcontext->type, tclass, qstr);
+				      tcontext->type, tclass, objname);
 
 	/* Check for class-specific changes. */
 	if (specified & AVTAB_TRANSITION) {
@@ -1539,13 +1539,14 @@ int security_transition_sid(u32 ssid, u32 tsid, u16 tclass,
 			    const struct qstr *qstr, u32 *out_sid)
 {
 	return security_compute_sid(ssid, tsid, tclass, AVTAB_TRANSITION,
-				    qstr, out_sid, true);
+				    qstr ? qstr->name : NULL, out_sid, true);
 }
 
-int security_transition_sid_user(u32 ssid, u32 tsid, u16 tclass, u32 *out_sid)
+int security_transition_sid_user(u32 ssid, u32 tsid, u16 tclass,
+				 const char *objname, u32 *out_sid)
 {
 	return security_compute_sid(ssid, tsid, tclass, AVTAB_TRANSITION,
-				    NULL, out_sid, false);
+				    objname, out_sid, false);
 }
 
 /**