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|
package main
import (
"fmt"
"os"
"path/filepath"
"runtime"
"syscall"
"time"
)
// pidfdGetfdSuccess duplicates an existing file descriptor through pidfd_getfd.
func pidfdGetfdSuccess() error {
dir, cleanup, err := makeTempDir("pidfd-getfd-success")
if err != nil {
return err
}
defer cleanup()
path := filepath.Join(dir, "pidfd-getfd-source.txt")
fd, err := syscall.Open(path, syscall.O_RDWR|syscall.O_CREAT, 0o644)
if err != nil {
return fmt.Errorf("open source: %w", err)
}
defer syscall.Close(fd)
pidfd, err := pidfdOpen(os.Getpid(), 0)
if err != nil {
return fmt.Errorf("pidfd_open self: %w", err)
}
defer syscall.Close(pidfd)
dupFd, err := pidfdGetfd(pidfd, fd, 0)
if err != nil {
return fmt.Errorf("pidfd_getfd: %w", err)
}
if _, err := syscall.Write(dupFd, []byte("via pidfd_getfd")); err != nil {
syscall.Close(dupFd)
return fmt.Errorf("write dup fd: %w", err)
}
// Keep the duplicated fd alive briefly so eventloop can resolve /proc fd path.
time.Sleep(500 * time.Millisecond)
if err := syscall.Close(dupFd); err != nil {
return fmt.Errorf("close dup fd: %w", err)
}
return nil
}
// pidfdGetfdFailure performs a guaranteed-failing pidfd_getfd call while
// also probing a cross-process call that may fail under ptrace/Yama policy.
func pidfdGetfdFailure() error {
pidfd, err := pidfdOpen(os.Getpid(), 0)
if err != nil {
return fmt.Errorf("pidfd_open self: %w", err)
}
defer syscall.Close(pidfd)
// Best-effort probe. Depending on kernel ptrace/Yama policy, this may fail
// with EPERM/EACCES; if it succeeds we close the returned fd and continue.
if initPidfd, err := pidfdOpen(1, 0); err == nil {
func() {
defer syscall.Close(initPidfd)
if probeFd, err := pidfdGetfd(initPidfd, 1, 0); err == nil {
syscall.Close(probeFd)
}
}()
}
_, err = pidfdGetfd(pidfd, 99999, 0)
if err == nil {
return fmt.Errorf("expected pidfd_getfd with invalid source fd to fail")
}
return nil
}
func pidfdOpen(pid int, flags uintptr) (int, error) {
syscallNr, err := pidfdOpenSyscallNr()
if err != nil {
return 0, err
}
fd, _, errno := syscall.Syscall(syscallNr, uintptr(pid), flags, 0)
if errno != 0 {
return 0, errno
}
return int(fd), nil
}
func pidfdGetfd(pidfd int, targetFd int, flags uintptr) (int, error) {
syscallNr, err := pidfdGetfdSyscallNr()
if err != nil {
return 0, err
}
fd, _, errno := syscall.Syscall(
syscallNr,
uintptr(pidfd),
uintptr(targetFd),
flags,
)
if errno != 0 {
return 0, errno
}
return int(fd), nil
}
func pidfdOpenSyscallNr() (uintptr, error) {
return pidfdOpenSyscallNrForArch(runtime.GOARCH)
}
func pidfdGetfdSyscallNr() (uintptr, error) {
return pidfdGetfdSyscallNrForArch(runtime.GOARCH)
}
func pidfdOpenSyscallNrForArch(arch string) (uintptr, error) {
// Go's syscall package does not expose pidfd constants on all toolchains.
switch arch {
case "amd64", "arm64":
return 434, nil
default:
return 0, fmt.Errorf("pidfd_open syscall number not defined for GOARCH=%s", arch)
}
}
func pidfdGetfdSyscallNrForArch(arch string) (uintptr, error) {
// Go's syscall package does not expose pidfd constants on all toolchains.
switch arch {
case "amd64", "arm64":
return 438, nil
default:
return 0, fmt.Errorf("pidfd_getfd syscall number not defined for GOARCH=%s", arch)
}
}
|
