On 08/28/2018 10:34 AM, Amir Goldstein wrote:
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.
<sigh> I can only truly test this on 4.14 (android's current top of tree) and on Hikey with that. Lack of due diligence for Top of Linux.
+ } + 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().
Ahhhh
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.
NFS export/import blocked on Android devices.
Thanks, Amir.
