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Fix file permission checking in the depot package #141

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merged 2 commits into from
Feb 8, 2022
Merged

Fix file permission checking in the depot package #141

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2f526e0
Fix file permission checking in the depot package
jdtw Feb 8, 2022
926763e
Fix typo
jdtw Feb 8, 2022
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13 changes: 10 additions & 3 deletions depot/depot.go
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@ package depot

import (
"errors"
"io/fs"
"io/ioutil"
"os"
"path/filepath"
Expand Down Expand Up @@ -98,10 +99,10 @@ func (d *FileDepot) Put(tag *Tag, data []byte) error {
return nil
}

// Check returns whether the file at the tag location exists and has the correct permissions
// Check returns whether the file at the tag location exists and has permissions at least as restrictive as the given tag.
func (d *FileDepot) Check(tag *Tag) bool {
name := d.path(tag.name)
if fi, err := os.Stat(name); err == nil && ^fi.Mode()&tag.perm == 0 {
if fi, err := os.Stat(name); err == nil && checkPermissions(tag.perm, fi.Mode()) {
return true
}
return false
Expand All @@ -113,12 +114,18 @@ func (d *FileDepot) check(tag *Tag) error {
if err != nil {
return err
}
if ^fi.Mode()&tag.perm != 0 {
if !checkPermissions(tag.perm, fi.Mode()) {
return errors.New("permission denied")
}
return nil
}

// checkPermissions returns true if the mode bits in file are a subset of required.
func checkPermissions(required, file fs.FileMode) bool {
// Clear the bits of required from file. The check passes if there are no remaining bits set.
return file&^required == 0
}

// Get reads the file specified by the tag
func (d *FileDepot) Get(tag *Tag) ([]byte, error) {
if err := d.check(tag); err != nil {
Expand Down
66 changes: 51 additions & 15 deletions depot/depot_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@ package depot

import (
"bytes"
"io/fs"
"os"
"testing"
)
Expand All @@ -29,10 +30,8 @@ const (
)

var (
tag = &Tag{"host.pem", 0600}
tag2 = &Tag{"host2.pem", 0600}
wrongTag = &Tag{"host.pem", 0666}
wrongTag2 = &Tag{"host.pem2", 0600}
tag = &Tag{"host.pem", 0600}
tag2 = &Tag{"host2.pem", 0600}
)

func getDepot(t *testing.T) *FileDepot {
Expand Down Expand Up @@ -96,19 +95,20 @@ func TestDepotCheckFailure(t *testing.T) {
d := getDepot(t)
defer os.RemoveAll(dir)

if err := d.Put(tag, []byte(data)); err != nil {
if err := d.Put(&Tag{"host.pem", 0600}, []byte(data)); err != nil {
t.Fatal("Failed putting file into Depot:", err)
}

if d.Check(wrongTag) {
t.Fatal("Expect not to checking out file with insufficient permission")
// host.pem was created with mode 0600, so the permission check for 0400 should fail...
if d.Check(&Tag{"host.pem", 0400}) {
t.Fatal("Expected check permissions failure")
}

if d.Check(wrongTag2) {
t.Fatal("Expect not to checking out file with nonexist name")
if d.Check(&Tag{"does-not-exist.pem", 0777}) {
t.Fatal("Expect check failure for non-existent file")
}

if err := d.Delete(tag); err != nil {
if err := d.Delete(&Tag{"host.pem", 0777}); err != nil {
t.Fatal("Failed to delete a tag:", err)
}
}
Expand All @@ -117,16 +117,17 @@ func TestDepotGetFailure(t *testing.T) {
d := getDepot(t)
defer os.RemoveAll(dir)

if err := d.Put(tag, []byte(data)); err != nil {
if err := d.Put(&Tag{"host.pem", 0600}, []byte(data)); err != nil {
t.Fatal("Failed putting file into Depot:", err)
}

if _, err := d.Get(wrongTag); err == nil {
t.Fatal("Expect not to checking out file with insufficient permission")
// host.pem was created with mode 0600, so the permission check for 0400 should fail...
if _, err := d.Get(&Tag{"host.pem", 0400}); err == nil {
t.Fatal("Expected permissions failure")
}

if _, err := d.Get(wrongTag2); err == nil {
t.Fatal("Expect not to checking out file with nonexist name")
if _, err := d.Get(&Tag{"does-not-exist.pem", 0777}); err == nil {
t.Fatal("Expect get failure for non-existent file")
}

if err := d.Delete(tag); err != nil {
Expand Down Expand Up @@ -174,3 +175,38 @@ func TestDepotGetFile(t *testing.T) {
t.Fatal("Failed setting permission")
}
}

func TestCheckPermissions(t *testing.T) {
tests := []struct {
required fs.FileMode
file fs.FileMode
want bool
}{
// If required is 0777, any file permissions should pass...
{0777, 0000, true},
{0777, 0666, true},
{0777, 0400, true},
// When required is 0400, anything with more bits set should fail...
{0400, 0600, false},
{0400, 0440, false},
{0400, 0004, false},
// required == file should pass...
{0000, 0000, true},
{0440, 0440, true},
{0600, 0600, true},
{0777, 0777, true},
// When required is 0660, anything with more bits set fails, and
// anything with fewer bits set succeeds...
{0660, 0664, false},
{0660, 0670, false},
{0660, 0760, false},
{0660, 0660, true},
{0660, 0600, true},
{0660, 0440, true},
}
for _, tc := range tests {
if got := checkPermissions(tc.required, tc.file); got != tc.want {
t.Errorf("checkPermissions(required=%o, file=%o) = %t, want %t", tc.required, tc.file, got, tc.want)
}
}
}