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// -*- Mode: Go; indent-tabs-mode: t -*-
/*
* Copyright (C) 2018 Canonical Ltd
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 3 as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
*/
package builtin
import (
"bytes"
"fmt"
"path/filepath"
"strings"
"github.com/snapcore/snapd/interfaces"
"github.com/snapcore/snapd/interfaces/apparmor"
apparmor_sandbox "github.com/snapcore/snapd/sandbox/apparmor"
"github.com/snapcore/snapd/snap"
)
type commonFilesInterface struct {
commonInterface
apparmorHeader string
extraPathValidate func(string) error
}
// filesAAPerm can either be files{Read,Write} and converted to a string
// expands into the right apparmor permissions for the files interface.
type filesAAPerm int
const (
filesRead filesAAPerm = iota
filesWrite
)
func (a filesAAPerm) String() string {
switch a {
case filesRead:
return "rk" // [r]ead and loc[k]
case filesWrite:
return "rwkl" // [r]ead, [w]rite, loc[k] and [l]ink//
}
panic(fmt.Sprintf("invalid perm: %d", a))
}
func formatPath(ip interface{}) (string, error) {
p, ok := ip.(string)
if !ok {
return "", fmt.Errorf("%[1]v (%[1]T) is not a string", ip)
}
prefix := ""
// Note that the {personal,system}-files interface impose
// limitations on the $HOME usage - system-files forbids it,
// personal only allows starting with $HOME in the path.
if strings.Contains(p, "$HOME") {
p = strings.Replace(p, "$HOME", "@{HOME}", -1)
prefix = "owner "
}
p = filepath.Clean(p)
p += "{,/,/**}"
return fmt.Sprintf("%s%q", prefix, p), nil
}
func allowPathAccess(buf *bytes.Buffer, perm filesAAPerm, paths []interface{}) error {
for _, rawPath := range paths {
p, err := formatPath(rawPath)
if err != nil {
return err
}
fmt.Fprintf(buf, "%s %s,\n", p, perm)
}
return nil
}
func (iface *commonFilesInterface) validatePaths(attrName string, paths []interface{}) error {
for _, npp := range paths {
np, ok := npp.(string)
if !ok {
return fmt.Errorf("%q must be a list of strings", attrName)
}
if err := iface.validateSinglePath(np); err != nil {
return err
}
}
return nil
}
func (iface *commonFilesInterface) validateSinglePath(np string) error {
if strings.HasSuffix(np, "/") {
return fmt.Errorf(`%q cannot end with "/"`, np)
}
p := filepath.Clean(np)
if p != np {
return fmt.Errorf("cannot use %q: try %q", np, filepath.Clean(np))
}
if strings.Contains(p, "~") {
return fmt.Errorf(`%q cannot contain "~"`, p)
}
if err := apparmor_sandbox.ValidateNoAppArmorRegexp(p); err != nil {
return err
}
// extraPathValidation must be implemented by the interface
// that build on top of the abstract commonFilesInterface
if iface.extraPathValidate == nil {
panic("extraPathValidate must be set when using the commonFilesInterface")
}
if err := iface.extraPathValidate(np); err != nil {
return err
}
return nil
}
func (iface *commonFilesInterface) BeforePreparePlug(plug *snap.PlugInfo) error {
hasValidAttr := false
for _, att := range []string{"read", "write"} {
if _, ok := plug.Attrs[att]; !ok {
continue
}
paths, ok := plug.Attrs[att].([]interface{})
if !ok {
return fmt.Errorf("cannot add %s plug: %q must be a list of strings", iface.name, att)
}
if err := iface.validatePaths(att, paths); err != nil {
return fmt.Errorf("cannot add %s plug: %s", iface.name, err)
}
hasValidAttr = true
}
if !hasValidAttr {
return fmt.Errorf(`cannot add %s plug: needs valid "read" or "write" attribute`, iface.name)
}
return nil
}
func (iface *commonFilesInterface) AppArmorConnectedPlug(spec *apparmor.Specification, plug *interfaces.ConnectedPlug, slot *interfaces.ConnectedSlot) error {
var reads, writes []interface{}
_ = plug.Attr("read", &reads)
_ = plug.Attr("write", &writes)
errPrefix := fmt.Sprintf(`cannot connect plug %s: `, plug.Name())
buf := bytes.NewBufferString(iface.apparmorHeader)
if err := allowPathAccess(buf, filesRead, reads); err != nil {
return fmt.Errorf("%s%v", errPrefix, err)
}
if err := allowPathAccess(buf, filesWrite, writes); err != nil {
return fmt.Errorf("%s%v", errPrefix, err)
}
spec.AddSnippet(buf.String())
return nil
}
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