On Thu, May 2, 2019 at 12:35 AM NeilBrown <neilb@xxxxxxxx> wrote: > > > If the upper and lower layers use incompatible ACL formats, it is not > possible to copy the ACL xttr from one to the other, so overlayfs > cannot work with them. > This happens particularly with NFSv4 which uses system.nfs4_acl, and > ext4 which uses system.posix_acl_access. > > If all ACLs actually make to Unix permissions, then there is no need > to copy up the ACLs, but overlayfs cannot determine this. > > So allow the sysadmin it assert that ACLs are not needed with a mount > option > honoracl=off > This causes the ACLs to not be copied, so filesystems with different > ACL formats can be overlaid together. > > Signed-off-by: NeilBrown <neilb@xxxxxxxx> > --- > Documentation/filesystems/overlayfs.txt | 24 ++++++++++++++++++++++++ > fs/overlayfs/copy_up.c | 9 +++++++-- > fs/overlayfs/dir.c | 2 +- > fs/overlayfs/overlayfs.h | 2 +- > fs/overlayfs/ovl_entry.h | 1 + > fs/overlayfs/super.c | 15 +++++++++++++++ > 6 files changed, 49 insertions(+), 4 deletions(-) > > diff --git a/Documentation/filesystems/overlayfs.txt b/Documentation/filesystems/overlayfs.txt > index eef7d9d259e8..7ad675940c93 100644 > --- a/Documentation/filesystems/overlayfs.txt > +++ b/Documentation/filesystems/overlayfs.txt > @@ -245,6 +245,30 @@ filesystem - future operations on the file are barely noticed by the > overlay filesystem (though an operation on the name of the file such as > rename or unlink will of course be noticed and handled). > > +ACL copy-up > +----------- > + > +When a file that only exists on the lower layer is modified it needs > +to be copied up to the upper layer. This means copying the metadata > +and (usually) the data (though see "Metadata only copy up" below). > +One part of the metadata can be problematic: the ACLs. > + > +Now all filesystems support ACLs, and when they do they don't all use > +the same format. A significant conflict appears between POSIX acls > +used on many local filesystems, and NFSv4 ACLs used with NFSv4. There > +two formats are, in general, not inter-convertible. > + > +If a site only uses regular Unix permissions (Read, Write, eXecute by > +User, Group and Other), then as these permissions are compatible with > +all ACLs, there is no need to copy ACLs. overlayfs cannot determine > +if this is the case itself. > + > +For this reason, overlayfs supports a mount option "honoracl=off" > +which causes ACLs, any "system." extended attribute, on the lower > +layer to be ignored and, particularly, not copied to the upper later. > +This allows NFSv4 to be overlaid with a local filesystem, but should > +only be used if the only access controls used on the filesystem are > +Unix permission bits. > I don't know. On the one hand "system." is not only ACLs. On the other hand, "honoracl=off" is not the same as -o noacl, but it sure sounds the same. I'd be a lot more comfortable with "ignore_xattrs=system.nfs4_acl" argument takes a comma separated list of xattr prefixes to ignore. ovl_is_private_xattr() can be generalized to ovl_is_ignored_xattr(), going over a blacklist of N>=1 which will also be called from ovl_can_list(), because there is no point in listing the ACLs that are ignored. right? Thanks, Amir.
