1 files changed, 123 insertions, 0 deletions
diff --git a/mount.go b/mount.go
new file mode 100644
index 00000000..68d689fe
--- /dev/null
+++ b/mount.go
@@ -0,0 +1,123 @@
+package hakurei
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	. "syscall"
+
+	"git.gensokyo.uk/security/hakurei/sandbox/vfs"
+)
+
+func (p *procPaths) bindMount(source, target string, flags uintptr, eq bool) error {
+	if eq {
+		msg.Verbosef("resolved %q flags %#x", target, flags)
+	} else {
+		msg.Verbosef("resolved %q on %q flags %#x", source, target, flags)
+	}
+
+	if err := Mount(source, target, "", MS_SILENT|MS_BIND|flags&MS_REC, ""); err != nil {
+		return wrapErrSuffix(err,
+			fmt.Sprintf("cannot mount %q on %q:", source, target))
+	}
+
+	var targetFinal string
+	if v, err := filepath.EvalSymlinks(target); err != nil {
+		return wrapErrSelf(err)
+	} else {
+		targetFinal = v
+		if targetFinal != target {
+			msg.Verbosef("target resolves to %q", targetFinal)
+		}
+	}
+
+	// final target path according to the kernel through proc
+	var targetKFinal string
+	{
+		var destFd int
+		if err := IgnoringEINTR(func() (err error) {
+			destFd, err = Open(targetFinal, O_PATH|O_CLOEXEC, 0)
+			return
+		}); err != nil {
+			return wrapErrSuffix(err,
+				fmt.Sprintf("cannot open %q:", targetFinal))
+		}
+		if v, err := os.Readlink(p.fd(destFd)); err != nil {
+			return wrapErrSelf(err)
+		} else if err = Close(destFd); err != nil {
+			return wrapErrSuffix(err,
+				fmt.Sprintf("cannot close %q:", targetFinal))
+		} else {
+			targetKFinal = v
+		}
+	}
+
+	mf := MS_NOSUID | flags&MS_NODEV | flags&MS_RDONLY
+	return hostProc.mountinfo(func(d *vfs.MountInfoDecoder) error {
+		n, err := d.Unfold(targetKFinal)
+		if err != nil {
+			if errors.Is(err, ESTALE) {
+				return msg.WrapErr(err,
+					fmt.Sprintf("mount point %q never appeared in mountinfo", targetKFinal))
+			}
+			return wrapErrSuffix(err,
+				"cannot unfold mount hierarchy:")
+		}
+
+		if err = remountWithFlags(n, mf); err != nil {
+			return err
+		}
+		if flags&MS_REC == 0 {
+			return nil
+		}
+
+		for cur := range n.Collective() {
+			err = remountWithFlags(cur, mf)
+			if err != nil && !errors.Is(err, EACCES) {
+				return err
+			}
+		}
+
+		return nil
+	})
+}
+
+func remountWithFlags(n *vfs.MountInfoNode, mf uintptr) error {
+	kf, unmatched := n.Flags()
+	if len(unmatched) != 0 {
+		msg.Verbosef("unmatched vfs options: %q", unmatched)
+	}
+
+	if kf&mf != mf {
+		return wrapErrSuffix(
+			Mount("none", n.Clean, "", MS_SILENT|MS_BIND|MS_REMOUNT|kf|mf, ""),
+			fmt.Sprintf("cannot remount %q:", n.Clean))
+	}
+	return nil
+}
+
+func mountTmpfs(fsname, name string, size int, perm os.FileMode) error {
+	target := toSysroot(name)
+	if err := os.MkdirAll(target, parentPerm(perm)); err != nil {
+		return wrapErrSelf(err)
+	}
+	opt := fmt.Sprintf("mode=%#o", perm)
+	if size > 0 {
+		opt += fmt.Sprintf(",size=%d", size)
+	}
+	return wrapErrSuffix(
+		Mount(fsname, target, "tmpfs", MS_NOSUID|MS_NODEV, opt),
+		fmt.Sprintf("cannot mount tmpfs on %q:", name))
+}
+
+func parentPerm(perm os.FileMode) os.FileMode {
+	pperm := 0755
+	if perm&0070 == 0 {
+		pperm &= ^0050
+	}
+	if perm&0007 == 0 {
+		pperm &= ^0005
+	}
+	return os.FileMode(pperm)
+}