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oci: use readonly mount to read user/group info #6478

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Merged
dmcgowan merged 1 commit into from
Jan 31, 2022
+26 −0
Merged

oci: use readonly mount to read user/group info #6478

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26 changes: 26 additions & 0 deletions oci/spec_opts.go
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Original file line number Diff line number Diff line change
Expand Up @@ -602,6 +602,8 @@ func WithUser(userstr string) SpecOpts {
if err != nil {
return err
}

mounts = tryReadonlyMounts(mounts)
return mount.WithTempMount(ctx, mounts, f)
default:
return fmt.Errorf("invalid USER value %s", userstr)
Expand Down Expand Up @@ -655,6 +657,8 @@ func WithUserID(uid uint32) SpecOpts {
if err != nil {
return err
}

mounts = tryReadonlyMounts(mounts)
return mount.WithTempMount(ctx, mounts, func(root string) error {
user, err := UserFromPath(root, func(u user.User) bool {
return u.Uid == int(uid)
Expand Down Expand Up @@ -706,6 +710,8 @@ func WithUsername(username string) SpecOpts {
if err != nil {
return err
}

mounts = tryReadonlyMounts(mounts)
return mount.WithTempMount(ctx, mounts, func(root string) error {
user, err := UserFromPath(root, func(u user.User) bool {
return u.Name == username
Expand Down Expand Up @@ -790,6 +796,8 @@ func WithAdditionalGIDs(userstr string) SpecOpts {
if err != nil {
return err
}

mounts = tryReadonlyMounts(mounts)
return mount.WithTempMount(ctx, mounts, setAdditionalGids)
}
}
Expand Down Expand Up @@ -1278,3 +1286,21 @@ func WithDevShmSize(kb int64) SpecOpts {
return ErrNoShmMount
}
}

// tryReadonlyMounts is used by the options which are trying to get user/group
// information from container's rootfs. Since the option does read operation
// only, this helper will append ReadOnly mount option to prevent linux kernel
// from syncing whole filesystem in umount syscall.
//
// TODO(fuweid):
//
// Currently, it only works for overlayfs. I think we can apply it to other
// kinds of filesystem. Maybe we can return `ro` option by `snapshotter.Mount`
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@jsoref jsoref Jan 28, 2022

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Suggested change
// kinds of filesystem. Maybe we can return `ro` option by `snapshotter.Mount`
// kinds of filesystems. Maybe we can return `ro` option by `snapshotter.Mount`

// API, when the caller passes that experimental annotation
// `containerd.io/snapshot/readonly.mount` something like that.
func tryReadonlyMounts(mounts []mount.Mount) []mount.Mount {
if len(mounts) == 1 && mounts[0].Type == "overlay" {
mounts[0].Options = append(mounts[0].Options, "ro")
}
return mounts
}