Re: [PATCH v2 3/6] tools/virtiofsd: xattr name mappings: Add option

[Ján Tomko]

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

> +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

> +on the server, and used as a new prefix.  It maybe empty

may be

> +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

Jano

signature.asc
Description: PGP signature