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//go:build linux
// SPDX-License-Identifier: MPL-2.0
/*
* libpathrs: safe path resolution on Linux
* Copyright (C) 2019-2025 Aleksa Sarai <cyphar@cyphar.com>
* Copyright (C) 2019-2025 SUSE LLC
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at https://mozilla.org/MPL/2.0/.
*/
// Package fdutils contains a few helper methods when dealing with *os.File and
// file descriptors.
package fdutils
import (
"fmt"
"os"
"golang.org/x/sys/unix"
"cyphar.com/go-pathrs/internal/libpathrs"
)
// DupFd makes a duplicate of the given fd.
func DupFd(fd uintptr, name string) (*os.File, error) {
newFd, err := unix.FcntlInt(fd, unix.F_DUPFD_CLOEXEC, 0)
if err != nil {
return nil, fmt.Errorf("fcntl(F_DUPFD_CLOEXEC): %w", err)
}
return os.NewFile(uintptr(newFd), name), nil
}
// WithFileFd is a more ergonomic wrapper around file.SyscallConn().Control().
func WithFileFd[T any](file *os.File, fn func(fd uintptr) (T, error)) (T, error) {
conn, err := file.SyscallConn()
if err != nil {
return *new(T), err
}
var (
ret T
innerErr error
)
if err := conn.Control(func(fd uintptr) {
ret, innerErr = fn(fd)
}); err != nil {
return *new(T), err
}
return ret, innerErr
}
// DupFile makes a duplicate of the given file.
func DupFile(file *os.File) (*os.File, error) {
return WithFileFd(file, func(fd uintptr) (*os.File, error) {
return DupFd(fd, file.Name())
})
}
// MkFile creates a new *os.File from the provided file descriptor. However,
// unlike os.NewFile, the file's Name is based on the real path (provided by
// /proc/self/fd/$n).
func MkFile(fd uintptr) (*os.File, error) {
fdPath := fmt.Sprintf("fd/%d", fd)
fdName, err := libpathrs.ProcReadlinkat(libpathrs.ProcDefaultRootFd, libpathrs.ProcThreadSelf, fdPath)
if err != nil {
_ = unix.Close(int(fd))
return nil, fmt.Errorf("failed to fetch real name of fd %d: %w", fd, err)
}
// TODO: Maybe we should prefix this name with something to indicate to
// users that they must not use this path as a "safe" path. Something like
// "//pathrs-handle:/foo/bar"?
return os.NewFile(fd, fdName), nil
}
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