On Tue, Aug 28, 2018 at 7:53 PM Mark Salyzyn <salyzyn@xxxxxxxxxxx> wrote:
>
> Assumption never checked, should fail if the mounter creds are not
> sufficient.
>
> Signed-off-by: Mark Salyzyn <salyzyn@xxxxxxxxxxx>
> Cc: Miklos Szeredi <miklos@xxxxxxxxxx>
> Cc: Jonathan Corbet <corbet@xxxxxxx>
> Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
> Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
> Cc: Amir Goldstein <amir73il@xxxxxxxxx>
> Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
> Cc: Stephen Smalley <sds@xxxxxxxxxxxxx>
> Cc: linux-unionfs@xxxxxxxxxxxxxxx
> Cc: linux-doc@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
>
> v5:
> - dependency of "overlayfs: override_creds=off option bypass creator_cred"
> ---
> fs/overlayfs/namei.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
> index c993dd8db739..84982b6525fb 100644
> --- a/fs/overlayfs/namei.c
> +++ b/fs/overlayfs/namei.c
> @@ -193,6 +193,11 @@ struct dentry *ovl_decode_real_fh(struct ovl_fh *fh, struct vfsmount *mnt,
> if (!uuid_equal(&fh->uuid, &mnt->mnt_sb->s_uuid))
> return NULL;
>
> + if (!capable(CAP_DAC_READ_SEARCH)) {
> + origin = ERR_PTR(-EPERM);
> + goto out;
Which branch is this works based on?
I don't see any out label in current code.
> + }
> +
> bytes = (fh->len - offsetof(struct ovl_fh, fid));
> real = exportfs_decode_fh(mnt, (struct fid *)fh->fid,
> bytes >> 2, (int)fh->type,
> --
Please add same test in ovl_can_decode_fh().
Problem: none of the ovl_export_operations functions override creds.
I guess things are working now because nfsd is privileged enough.
IOW, the capability check you added doesn't check mounter creds
when coming from nfs export ops - I guess that is not what you want
although you probably don'r enable nfs export.
Thanks,
Amir.
