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Re: [PATCH v2 3/6] tools/virtiofsd: xattr name mappings: Add option
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [PATCH v2 3/6] tools/virtiofsd: xattr name mappings: Add option |
Date: |
Thu, 10 Sep 2020 19:38:46 +0100 |
User-agent: |
Mutt/1.14.6 (2020-07-11) |
* Ján Tomko (jtomko@redhat.com) wrote:
> On a Thursday in 2020, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> >
> > Add an option to define mappings of xattr names so that
> > the client and server filesystems see different views.
> > This can be used to have different SELinux mappings as
> > seen by the guest, to run the virtiofsd with less privileges
> > (e.g. in a case where it can't set trusted/system/security
> > xattrs but you want the guest to be able to), or to isolate
> > multiple users of the same name; e.g. trusted attributes
> > used by stacking overlayfs.
> >
> > A mapping engine is used wit 3 simple rules; the rules can
> > be combined to allow most useful mapping scenarios.
> > The ruleset is defined by -o xattrmap='rules...'.
> >
> > This patch doesn't use the rule maps yet.
> >
> > Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > ---
> > docs/tools/virtiofsd.rst | 55 ++++++++++++
> > tools/virtiofsd/passthrough_ll.c | 148 +++++++++++++++++++++++++++++++
> > 2 files changed, 203 insertions(+)
> >
> > diff --git a/docs/tools/virtiofsd.rst b/docs/tools/virtiofsd.rst
> > index 824e713491..2efa16d3c5 100644
> > --- a/docs/tools/virtiofsd.rst
> > +++ b/docs/tools/virtiofsd.rst
> > @@ -107,6 +107,60 @@ Options
> > performance. ``auto`` acts similar to NFS with a 1 second metadata cache
> > timeout. ``always`` sets a long cache lifetime at the expense of
> > coherency.
> >
> > +xattr-mapping
> > +-------------
> > +
> > +By default the name of xattr's used by the client are passed through to
> > the server
> > +file system. This can be a problem where either those xattr names are used
> > +by something on the server (e.g. selinux client/server confusion) or if the
> > +virtiofsd is running in a container with restricted priviliges where it
> > cannot
>
> privileges
Fixed.
> > +access some attributes.
> > +
> > +A mapping of xattr names can be made using -o xattrmap=mapping where the
> > ``mapping``
> > +string consists of a series of rules.
> > +
> > +The first matching rule terminates the mapping.
> > +
> > +Each rule consists of a number of fields separated with a separator that
> > is the
> > +first non-white space character in the rule. This separator must then be
> > used
> > +for the whole rule.
> > +White space may be added before and after each rule.
> > +Using ':' as the separator a rule is of the form:
> > +
> > +``:scope:type:key:prepend:``
> > +
> > +**scope** is:
> > +
> > +- 'client' - match 'key' against a xattr name from the client for
> > + setxattr/getxattr/removexattr
> > +- 'server' - match 'prepend' against a xattr name from the server
> > + for listxattr
> > +- 'all' - can be used to match both cases.
> > +
> > +**type** is one of:
> > +
> > +- 'prefix' - If 'key' matches the client then the 'prepend'
> > + is added before the name is passed to the server.
> > + For a server case, the prepend is tested and stripped
> > + if matching.
> > +
> > +- 'ok' - The attribute name is OK and passed through to
> > + the server unchanged.
> > +
> > +- 'bad' - If a client tries to use this name it's
> > + denied using EPERM; when the server passes an attribute
> > + name matching it's hidden.
> > +
> > +**key** is a string tested as a prefix on an attribute name originating
> > +on the client. It maybe empty in which case a 'client' rule
> > +will always match on client names.
> > +
> > +**prepend** is a string tested as a prefix on an attribute name
> > originiating
>
> originating
Done.
> > +on the server, and used as a new prefix. It maybe empty
>
> may be
OK
> > +in which case a 'server' rule will always match on all names from
> > +the server.
> > +
> > +
> > Examples
> > --------
> >
> > @@ -123,3 +177,4 @@ Export ``/var/lib/fs/vm001/`` on vhost-user UNIX domain
> > socket
> > -numa node,memdev=mem \
> > ...
> > guest# mount -t virtiofs myfs /mnt
> > +
>
> git complains about trailing whitespace at EOF
Eaten.
Dave
> Jano
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK