[Virtio-fs] [PATCH v5 9/9] virtiofsd: Add an option to enable/disable security label

[Vivek Goyal]

On Mon, Feb 07, 2022 at 12:40:21PM +0000, Dr. David Alan Gilbert wrote:
> * Vivek Goyal (vgoyal at redhat.com) wrote:
> > Provide an option "-o security_label/no_security_label" to enable/disable
> > security label functionality. By default these are turned off.
> > 
> > If enabled, server will indicate to client that it is capable of handling
> > one security label during file creation. Typically this is expected to
> > be a SELinux label. File server will set this label on the file. It will
> > try to set it atomically wherever possible. But its not possible in
> > all the cases.
> > 
> > Signed-off-by: Vivek Goyal <vgoyal at redhat.com>
> > ---
> >  docs/tools/virtiofsd.rst         |  7 +++++++
> >  tools/virtiofsd/helper.c         |  1 +
> >  tools/virtiofsd/passthrough_ll.c | 15 +++++++++++++++
> >  3 files changed, 23 insertions(+)
> > 
> > diff --git a/docs/tools/virtiofsd.rst b/docs/tools/virtiofsd.rst
> > index 07ac0be551..a2c005f4a0 100644
> > --- a/docs/tools/virtiofsd.rst
> > +++ b/docs/tools/virtiofsd.rst
> > @@ -104,6 +104,13 @@ Options
> >    * posix_acl|no_posix_acl -
> >      Enable/disable posix acl support.  Posix ACLs are disabled by default.
> >  
> > +  * security_label|no_security_label -
> > +    Enable/disable security label support. Security labels are disabled by
> > +    default. This will allow client to send a MAC label of file during
>                                 ^ the                        ^ a
> > +    file creation. Typically this is expected to be SELinux security
>                                                       ^ an
> 
> > +    label. Server will try to set that label on newly created file
>               ^The server
> > +    atomically wherever possible.
> > +
> >  .. option:: --socket-path=PATH
> >  
> >    Listen on vhost-user UNIX domain socket at PATH.
> > diff --git a/tools/virtiofsd/helper.c b/tools/virtiofsd/helper.c
> > index a8295d975a..e226fc590f 100644
> > --- a/tools/virtiofsd/helper.c
> > +++ b/tools/virtiofsd/helper.c
> > @@ -187,6 +187,7 @@ void fuse_cmdline_help(void)
> >             "                               default: no_allow_direct_io\n"
> >             "    -o announce_submounts      Announce sub-mount points to the guest\n"
> >             "    -o posix_acl/no_posix_acl  Enable/Disable posix_acl. (default: disabled)\n"
> > +           "    -o security_label/no_security_label  Enable/Disable security label. (default: disabled)\n"
> >             );
> >  }
> >  
> > diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
> > index 43c9b6dbe5..fe8f3ccbb6 100644
> > --- a/tools/virtiofsd/passthrough_ll.c
> > +++ b/tools/virtiofsd/passthrough_ll.c
> > @@ -181,6 +181,7 @@ struct lo_data {
> >      int user_posix_acl, posix_acl;
> >      /* Keeps track if /proc/<pid>/attr/fscreate should be used or not */
> >      bool use_fscreate;
> > +    int user_security_label;
> >  };
> >  
> >  static const struct fuse_opt lo_opts[] = {
> > @@ -215,6 +216,8 @@ static const struct fuse_opt lo_opts[] = {
> >      { "no_killpriv_v2", offsetof(struct lo_data, user_killpriv_v2), 0 },
> >      { "posix_acl", offsetof(struct lo_data, user_posix_acl), 1 },
> >      { "no_posix_acl", offsetof(struct lo_data, user_posix_acl), 0 },
> > +    { "security_label", offsetof(struct lo_data, user_security_label), 1 },
> > +    { "no_security_label", offsetof(struct lo_data, user_security_label), 0 },
> >      FUSE_OPT_END
> >  };
> >  static bool use_syslog = false;
> > @@ -771,6 +774,17 @@ static void lo_init(void *userdata, struct fuse_conn_info *conn)
> >          fuse_log(FUSE_LOG_DEBUG, "lo_init: disabling posix_acl\n");
> >          conn->want &= ~FUSE_CAP_POSIX_ACL;
> >      }
> > +
> > +    if (lo->user_security_label == 1) {
> > +        if (!(conn->capable & FUSE_CAP_SECURITY_CTX)) {
> > +            fuse_log(FUSE_LOG_ERR, "lo_init: Can not enable security label."
> > +                     " kernel does not support FUSE_SECURITY_CTX capability.\n");
> > +        }
> 
> Do you need to exit in this case - or at least clear the flag?

Actually we don't have to necessarily exit here because fuse_lowlevel.c
has a check which makes it exit. And that's why I do not clear the
flag from ->want to signifiy that filesystem wants that capability
but client is not ->capable so error out and exit.


    if (se->conn.want & (~se->conn.capable)) {
        fuse_log(FUSE_LOG_ERR,
                 "fuse: error: filesystem requested capabilities "
                 "0x%llx that are not supported by kernel, aborting.\n",
                 se->conn.want & (~se->conn.capable));
        fuse_reply_err(req, EPROTO);
        se->error = -EPROTO;
        fuse_session_exit(se);
        return;
    }

Thanks
Vivek

> 
> Dave
> 
> > +        conn->want |= FUSE_CAP_SECURITY_CTX;
> > +    } else {
> > +        fuse_log(FUSE_LOG_DEBUG, "lo_init: disabling security label\n");
> > +        conn->want &= ~FUSE_CAP_SECURITY_CTX;
> > +    }
> >  }
> >  
> >  static void lo_getattr(fuse_req_t req, fuse_ino_t ino,
> > @@ -4279,6 +4293,7 @@ int main(int argc, char *argv[])
> >          .proc_self_task = -1,
> >          .user_killpriv_v2 = -1,
> >          .user_posix_acl = -1,
> > +        .user_security_label = -1,
> >      };
> >      struct lo_map_elem *root_elem;
> >      struct lo_map_elem *reserve_elem;
> > -- 
> > 2.34.1
> > 
> -- 
> Dr. David Alan Gilbert / dgilbert at redhat.com / Manchester, UK
>