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117 lines
3.7 KiB
Go
117 lines
3.7 KiB
Go
//go:build !windows
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// +build !windows
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package utils
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import (
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"fmt"
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"os"
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"strconv"
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_ "unsafe" // for go:linkname
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"golang.org/x/sys/unix"
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)
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// EnsureProcHandle returns whether or not the given file handle is on procfs.
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func EnsureProcHandle(fh *os.File) error {
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var buf unix.Statfs_t
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if err := unix.Fstatfs(int(fh.Fd()), &buf); err != nil {
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return fmt.Errorf("ensure %s is on procfs: %w", fh.Name(), err)
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}
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if buf.Type != unix.PROC_SUPER_MAGIC {
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return fmt.Errorf("%s is not on procfs", fh.Name())
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}
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return nil
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}
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type fdFunc func(fd int)
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// fdRangeFrom calls the passed fdFunc for each file descriptor that is open in
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// the current process.
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func fdRangeFrom(minFd int, fn fdFunc) error {
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fdDir, err := os.Open("/proc/self/fd")
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if err != nil {
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return err
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}
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defer fdDir.Close()
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if err := EnsureProcHandle(fdDir); err != nil {
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return err
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}
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fdList, err := fdDir.Readdirnames(-1)
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if err != nil {
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return err
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}
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for _, fdStr := range fdList {
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fd, err := strconv.Atoi(fdStr)
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// Ignore non-numeric file names.
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if err != nil {
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continue
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}
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// Ignore descriptors lower than our specified minimum.
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if fd < minFd {
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continue
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}
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// Ignore the file descriptor we used for readdir, as it will be closed
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// when we return.
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if uintptr(fd) == fdDir.Fd() {
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continue
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}
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// Run the closure.
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fn(fd)
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}
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return nil
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}
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// CloseExecFrom sets the O_CLOEXEC flag on all file descriptors greater or
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// equal to minFd in the current process.
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func CloseExecFrom(minFd int) error {
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return fdRangeFrom(minFd, unix.CloseOnExec)
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}
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//go:linkname runtime_IsPollDescriptor internal/poll.IsPollDescriptor
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// In order to make sure we do not close the internal epoll descriptors the Go
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// runtime uses, we need to ensure that we skip descriptors that match
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// "internal/poll".IsPollDescriptor. Yes, this is a Go runtime internal thing,
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// unfortunately there's no other way to be sure we're only keeping the file
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// descriptors the Go runtime needs. Hopefully nothing blows up doing this...
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func runtime_IsPollDescriptor(fd uintptr) bool //nolint:revive
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// UnsafeCloseFrom closes all file descriptors greater or equal to minFd in the
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// current process, except for those critical to Go's runtime (such as the
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// netpoll management descriptors).
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//
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// NOTE: That this function is incredibly dangerous to use in most Go code, as
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// closing file descriptors from underneath *os.File handles can lead to very
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// bad behaviour (the closed file descriptor can be re-used and then any
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// *os.File operations would apply to the wrong file). This function is only
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// intended to be called from the last stage of runc init.
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func UnsafeCloseFrom(minFd int) error {
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// We must not close some file descriptors.
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return fdRangeFrom(minFd, func(fd int) {
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if runtime_IsPollDescriptor(uintptr(fd)) {
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// These are the Go runtimes internal netpoll file descriptors.
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// These file descriptors are operated on deep in the Go scheduler,
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// and closing those files from underneath Go can result in panics.
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// There is no issue with keeping them because they are not
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// executable and are not useful to an attacker anyway. Also we
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// don't have any choice.
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return
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}
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// There's nothing we can do about errors from close(2), and the
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// only likely error to be seen is EBADF which indicates the fd was
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// already closed (in which case, we got what we wanted).
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_ = unix.Close(fd)
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})
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}
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// NewSockPair returns a new unix socket pair
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func NewSockPair(name string) (parent *os.File, child *os.File, err error) {
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fds, err := unix.Socketpair(unix.AF_LOCAL, unix.SOCK_STREAM|unix.SOCK_CLOEXEC, 0)
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if err != nil {
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return nil, nil, err
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}
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return os.NewFile(uintptr(fds[1]), name+"-p"), os.NewFile(uintptr(fds[0]), name+"-c"), nil
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}
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