[refpolicy] [PATCH v3] xserver: restrict executable memory permissions

[pebenito@ieee.org (Chris PeBenito)]

On 12/29/16 19:36, Guido Trentalancia via refpolicy wrote:
> The dangerous execheap permission is removed from xdm and the
> dangerous execmem permission is only enabled for the Gnome
> Display Manager (gnome-shell running in gdm mode) through a
> new "gnome_xdm" boolean.
>
> This patch also updates the XKB libs file context with their
> default location, adds the ability to read udev pid files and
> finally adds a few permissions so that xconsole can run smoothly.
>
> Signed-off-by: Guido Trentalancia <guido@trentalancia.net>
> ---
>  policy/modules/services/xserver.fc |    2 ++
>  policy/modules/services/xserver.te |   24 +++++++++++++++++++-----
>  2 files changed, 21 insertions(+), 5 deletions(-)
>
> diff -pru a/policy/modules/services/xserver.fc b/policy/modules/services/xserver.fc
> --- a/policy/modules/services/xserver.fc	2016-12-22 23:12:47.782929703 +0100
> +++ b/policy/modules/services/xserver.fc	2016-12-30 01:25:51.383728583 +0100
> @@ -79,6 +79,8 @@ HOME_DIR/\.Xauthority.*	--	gen_context(s
>
>  /usr/sbin/lightdm	--	gen_context(system_u:object_r:xdm_exec_t,s0)
>
> +/usr/share/X11/xkb(/.*)?	gen_context(system_u:object_r:xkb_var_lib_t,s0)
> +
>  /usr/X11R6/bin/[xgkw]dm	--	gen_context(system_u:object_r:xdm_exec_t,s0)
>  /usr/X11R6/bin/iceauth	--	gen_context(system_u:object_r:iceauth_exec_t,s0)
>  /usr/X11R6/bin/X	--	gen_context(system_u:object_r:xserver_exec_t,s0)
> diff -pru a/policy/modules/services/xserver.te b/policy/modules/services/xserver.te
> --- a/policy/modules/services/xserver.te	2016-12-22 23:12:47.782929703 +0100
> +++ b/policy/modules/services/xserver.te	2016-12-30 01:30:43.634289624 +0100
> @@ -42,6 +42,14 @@ gen_tunable(xdm_sysadm_login, false)
>
>  ## <desc>
>  ## <p>
> +## Use gnome-shell in gdm mode as the
> +## X Display Manager (XDM)
> +## </p>
> +## </desc>
> +gen_tunable(gnome_xdm, false)

The tunable name should start with xserver.


> +## <desc>
> +## <p>
>  ## Support X userspace object manager
>  ## </p>
>  ## </desc>
> @@ -304,6 +312,7 @@ optional_policy(`
>  #
>
>  allow xdm_t self:capability { setgid setuid sys_resource kill sys_tty_config mknod chown dac_override dac_read_search fowner fsetid ipc_owner sys_nice sys_rawio net_bind_service };
> +dontaudit xdm_t self:capability sys_admin;
>  allow xdm_t self:process { setexec setpgid getsched setsched setrlimit signal_perms };
>  allow xdm_t self:fifo_file rw_fifo_file_perms;
>  allow xdm_t self:shm create_shm_perms;
> @@ -316,7 +325,7 @@ allow xdm_t self:socket create_socket_pe
>  allow xdm_t self:appletalk_socket create_socket_perms;
>  allow xdm_t self:key { search link write };
>
> -allow xdm_t xconsole_device_t:fifo_file { getattr setattr };
> +allow xdm_t xconsole_device_t:fifo_file read_fifo_file_perms;

The setattr permission is lost.

>  # Allow gdm to run gdm-binary
>  can_exec(xdm_t, xdm_exec_t)
> @@ -450,6 +459,10 @@ term_setattr_console(xdm_t)
>  term_use_unallocated_ttys(xdm_t)
>  term_setattr_unallocated_ttys(xdm_t)
>
> +# for xconsole
> +term_use_ptmx(xdm_t)
> +term_use_generic_ptys(xdm_t)

Looks like a pty needs to be properly labeled.


>  auth_domtrans_pam_console(xdm_t)
>  auth_manage_pam_pid(xdm_t)
>  auth_manage_pam_console_data(xdm_t)
> @@ -507,6 +520,10 @@ tunable_policy(`xdm_sysadm_login',`
>  #	allow xserver_t xdm_tmpfs_t:file rw_file_perms;
>  ')
>
> +tunable_policy(`gnome_xdm',`
> +	allow xdm_t self:process execmem;
> +')
> +
>  optional_policy(`
>  	alsa_domtrans(xdm_t)
>  ')
> @@ -586,10 +603,6 @@ optional_policy(`
>  optional_policy(`
>  	unconfined_domain(xdm_t)
>  	unconfined_domtrans(xdm_t)
> -
> -	ifndef(`distro_redhat',`
> -		allow xdm_t self:process { execheap execmem };
> -	')
>  ')
>
>  optional_policy(`
> @@ -803,6 +816,7 @@ optional_policy(`
>
>  optional_policy(`
>  	udev_read_db(xserver_t)
> +	udev_read_pid_files(xserver_t)
>  ')
>
>  optional_policy(`



-- 
Chris PeBenito