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//go:build linux
package binfmt
import (
"bufio"
"errors"
"fmt"
"os"
"path/filepath"
"strings"
"syscall"
"github.com/containers/storage/pkg/unshare"
"github.com/sirupsen/logrus"
"golang.org/x/sys/unix"
)
// MaybeRegister() calls Register() if the current context is a rootless one,
// or if the "container" environment variable suggests that we're in a
// container.
func MaybeRegister(configurationSearchDirectories []string) error {
if unshare.IsRootless() || os.Getenv("container") != "" { // we _also_ own our own mount namespace
return Register(configurationSearchDirectories)
}
return nil
}
// Register() registers binfmt.d emulators described by configuration files in
// the passed-in slice of directories, or in the union of /etc/binfmt.d,
// /run/binfmt.d, and /usr/lib/binfmt.d if the slice has no items. If any
// emulators are configured, it will attempt to mount a binfmt_misc filesystem
// in the current mount namespace first, ignoring only EPERM and EACCES errors.
func Register(configurationSearchDirectories []string) error {
if len(configurationSearchDirectories) == 0 {
configurationSearchDirectories = []string{"/etc/binfmt.d", "/run/binfmt.d", "/usr/lib/binfmt.d"}
}
mounted := false
for _, searchDir := range configurationSearchDirectories {
globs, err := filepath.Glob(filepath.Join(searchDir, "*.conf"))
if err != nil {
return fmt.Errorf("looking for binfmt.d configuration in %q: %w", searchDir, err)
}
for _, conf := range globs {
f, err := os.Open(conf)
if err != nil {
return fmt.Errorf("reading binfmt.d configuration: %w", err)
}
scanner := bufio.NewScanner(f)
for scanner.Scan() {
line := strings.TrimSpace(scanner.Text())
if len(line) == 0 || line[0] == ';' || line[0] == '#' {
continue
}
if !mounted {
if err = unix.Mount("none", "/proc/sys/fs/binfmt_misc", "binfmt_misc", 0, ""); err != nil {
if errors.Is(err, syscall.EPERM) || errors.Is(err, syscall.EACCES) {
// well, we tried. no need to make a stink about it
return nil
}
return fmt.Errorf("mounting binfmt_misc: %w", err)
}
mounted = true
}
reg, err := os.Create("/proc/sys/fs/binfmt_misc/register")
if err != nil {
return fmt.Errorf("registering(open): %w", err)
}
if _, err = fmt.Fprintf(reg, "%s\n", line); err != nil {
return fmt.Errorf("registering(write): %w", err)
}
logrus.Tracef("registered binfmt %q", line)
if err = reg.Close(); err != nil {
return fmt.Errorf("registering(close): %w", err)
}
}
if err := f.Close(); err != nil {
return fmt.Errorf("reading binfmt.d configuration: %w", err)
}
}
}
return nil
}
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