Initial Commit

fakeroot.go

@@ -0,0 +1,71 @@
+package fakeroot
+
+import (
+	"errors"
+	"os"
+	"os/exec"
+	"slices"
+	"syscall"
+)
+
+var (
+	// ErrRootUIDAlreadyMapped is returned when there's already a mapping for the root user in a command
+	ErrRootUIDAlreadyMapped = errors.New("fakeroot: root user has already been mapped in this command")
+
+	// ErrRootGIDAlreadyMapped is returned when there's already a mapping for the root group in a command
+	ErrRootGIDAlreadyMapped = errors.New("fakeroot: root group has already been mapped in this command")
+)
+
+// Command returns a command that runs in a fakeroot environment
+func Command(name string, arg ...string) (*exec.Cmd, error) {
+	cmd := exec.Command(name, arg...)
+	return cmd, Apply(cmd)
+}
+
+// Apply applies the options required to run in a fakeroot environment to
+// a command. It returns an error if the root group or user already has a mapping
+// registered in the command.
+func Apply(cmd *exec.Cmd) error {
+	uid := os.Getuid()
+
+	// If the user is already root, there's no need for fakeroot
+	if uid == 0 {
+		return nil
+	}
+
+	// Ensure SysProcAttr isn't nil
+	if cmd.SysProcAttr == nil {
+		cmd.SysProcAttr = &syscall.SysProcAttr{}
+	}
+
+	// Create a new user namespace
+	cmd.SysProcAttr.Cloneflags |= syscall.CLONE_NEWUSER
+
+	// If the command already contains a mapping for the root user, return an error
+	if slices.ContainsFunc(cmd.SysProcAttr.UidMappings, rootMap) {
+		return ErrRootUIDAlreadyMapped
+	}
+
+	// If the command already contains a mapping for the root group, return an error
+	if slices.ContainsFunc(cmd.SysProcAttr.GidMappings, rootMap) {
+		return ErrRootGIDAlreadyMapped
+	}
+
+	cmd.SysProcAttr.UidMappings = append(cmd.SysProcAttr.UidMappings, syscall.SysProcIDMap{
+		ContainerID: 0,
+		HostID:      uid,
+		Size:        1,
+	})
+
+	cmd.SysProcAttr.GidMappings = append(cmd.SysProcAttr.GidMappings, syscall.SysProcIDMap{
+		ContainerID: 0,
+		HostID:      uid,
+		Size:        1,
+	})
+
+	return nil
+}
+
+func rootMap(m syscall.SysProcIDMap) bool {
+	return m.ContainerID == 0
+}