diff --git a/sys/mount_linux.go b/sys/mount_linux.go index a9eee9b73..a21045529 100644 --- a/sys/mount_linux.go +++ b/sys/mount_linux.go @@ -21,6 +21,7 @@ import ( "syscall" "unsafe" + "github.com/containerd/containerd/log" "github.com/pkg/errors" "golang.org/x/sys/unix" ) @@ -30,9 +31,8 @@ func FMountat(dirfd uintptr, source, target, fstype string, flags uintptr, data var ( sourceP, targetP, fstypeP, dataP *byte pid uintptr - ws unix.WaitStatus err error - errno syscall.Errno + errno, status syscall.Errno ) sourceP, err = syscall.BytePtrFromString(source) @@ -60,37 +60,62 @@ func FMountat(dirfd uintptr, source, target, fstype string, flags uintptr, data runtime.LockOSThread() defer runtime.UnlockOSThread() + var pipefds [2]int + if err := syscall.Pipe2(pipefds[:], syscall.O_CLOEXEC); err != nil { + return errors.Wrap(err, "failed to open pipe") + } + + defer func() { + // close both ends of the pipe in a deferred function, since open file + // descriptor table is shared with child + syscall.Close(pipefds[0]) + syscall.Close(pipefds[1]) + }() + pid, errno = forkAndMountat(dirfd, uintptr(unsafe.Pointer(sourceP)), uintptr(unsafe.Pointer(targetP)), uintptr(unsafe.Pointer(fstypeP)), flags, - uintptr(unsafe.Pointer(dataP))) + uintptr(unsafe.Pointer(dataP)), + pipefds[1], + ) if errno != 0 { return errors.Wrap(errno, "failed to fork thread") } - _, err = unix.Wait4(int(pid), &ws, 0, nil) - for err == syscall.EINTR { - _, err = unix.Wait4(int(pid), &ws, 0, nil) - } + defer func() { + _, err := unix.Wait4(int(pid), nil, 0, nil) + for err == syscall.EINTR { + _, err = unix.Wait4(int(pid), nil, 0, nil) + } - if err != nil { - return errors.Wrapf(err, "failed to find pid=%d process", pid) - } + if err != nil { + log.L.WithError(err).Debugf("failed to find pid=%d process", pid) + } + }() - errno = syscall.Errno(ws.ExitStatus()) + _, _, errno = syscall.RawSyscall(syscall.SYS_READ, + uintptr(pipefds[0]), + uintptr(unsafe.Pointer(&status)), + unsafe.Sizeof(status)) if errno != 0 { - return errors.Wrap(errno, "failed to mount") + return errors.Wrap(errno, "failed to read pipe") } + + if status != 0 { + return errors.Wrap(status, "failed to mount") + } + return nil } // forkAndMountat will fork thread, change working dir and mount. // // precondition: the runtime OS thread must be locked. -func forkAndMountat(dirfd uintptr, source, target, fstype, flags, data uintptr) (pid uintptr, errno syscall.Errno) { +func forkAndMountat(dirfd uintptr, source, target, fstype, flags, data uintptr, pipefd int) (pid uintptr, errno syscall.Errno) { + // block signal during clone beforeFork() @@ -114,6 +139,7 @@ func forkAndMountat(dirfd uintptr, source, target, fstype, flags, data uintptr) _, _, errno = syscall.RawSyscall6(syscall.SYS_MOUNT, source, target, fstype, flags, data, 0) childerr: + _, _, errno = syscall.RawSyscall(syscall.SYS_WRITE, uintptr(pipefd), uintptr(unsafe.Pointer(&errno)), unsafe.Sizeof(errno)) syscall.RawSyscall(syscall.SYS_EXIT, uintptr(errno), 0, 0) panic("unreachable") }