disk: new path policies struct and methods

Build a new path policy struct, ased on the new path trie struct.
It is designed to be able to store policies for paths. A Check
method can then be used to look up the policy for a given path
based on the defined policies.

internal/disk/path_policy.go

@@ -0,0 +1,54 @@
+package disk
+
+import (
+	"fmt"
+	"path"
+)
+
+type PathPolicy struct {
+	Deny  bool // explicitly do not allow this entry
+	Exact bool // require and exact match, no subdirs
+}
+
+type PathPolicies = PathTrie
+
+// Create a new PathPolicies trie from a map of path to PathPolicy
+func NewPathPolicies(entries map[string]PathPolicy) *PathPolicies {
+
+	noType := make(map[string]interface{}, len(entries))
+
+	for k, v := range entries {
+		noType[k] = v
+	}
+
+	return NewPathTrieFromMap(noType)
+}
+
+// Check a given path at dir against the PathPolicies
+func (pol *PathPolicies) Check(dir string) error {
+
+	// Quickly check we have a mountpoint and it is absolute
+	if dir == "" || dir[0] != '/' {
+		return fmt.Errorf("mountpoint must be absolute path")
+	}
+
+	// ensure that only clean mountpoints are valid
+	if dir != path.Clean(dir) {
+		return fmt.Errorf("mountpoint must be a canonical path")
+	}
+
+	node, left := pol.Lookup(dir)
+	policy, ok := node.Payload.(PathPolicy)
+	if !ok {
+		panic("programming error: invalid path trie payload")
+	}
+
+	// 1) path is explicitly not allowed or
+	// 2) a subpath was match but an explicit match is required
+	if policy.Deny || (policy.Exact && len(left) > 0) {
+		return fmt.Errorf("path '%s ' is not allowed", dir)
+	}
+
+	// exact match or recursive mountpoints allowed
+	return nil
+}

internal/disk/path_policy_test.go

@@ -0,0 +1,50 @@
+package disk
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestPathPolicyCheck(t *testing.T) {
+	assert := assert.New(t)
+
+	entires := map[string]PathPolicy{
+		"/":          {Exact: true},
+		"/boot":      {Exact: true},
+		"/boot/efi":  {Exact: true},
+		"/var":       {},
+		"/var/empty": {Deny: true},
+		"/srv":       {},
+		"/home":      {},
+	}
+
+	policies := NewPathPolicies(entires)
+	assert.NotNil(policies)
+
+	tests := map[string]bool{
+		"/":                true,
+		"/custom":          false,
+		"/boot":            true,
+		"/boot/grub2":      false,
+		"/boot/efi":        true,
+		"/boot/efi/redora": false,
+		"/srv":             true,
+		"/srv/www":         true,
+		"/srv/www/data":    true,
+		"/var":             true,
+		"/var/log":         true,
+		"/var/empty":       false,
+		"/var/empty/dir":   false,
+	}
+
+	for k, v := range tests {
+		err := policies.Check(k)
+		if v {
+			assert.NoError(err)
+		} else {
+			assert.Errorf(err, "unexpected error for path '%s'", k)
+
+		}
+	}
+}