SecurityPolicy(5)

NAME
SecurityPolicy - X Window System SECURITY Extension Policy file format

DESCRIPTION
The SECURITY extension to the X Window System uses a policy file to determine which operations should be allowed or denied. The default location for this file is /usr/lib/xserver/SecurityPolicy.

The syntax of the security policy file is as follows. Notation: "*" means zero or more occurrences of the preceding element, and "+" means one or more occurrences. To interpret <foo/bar>, ignore the text after the /; it is used to distinguish between instances of <foo> in the next section.

<policy file> ::= <version line> <other line>*
<version line> ::= <string/v> '\n'
<other line > ::= <comment> | <access rule> | <site policy> | <blank line>
<comment> ::= # <not newline>* '\n'
<blank line> ::= <space> '\n'
<site policy> ::= sitepolicy <string/sp> '\n'
<access rule> ::= property <property/ar> <window> <perms> '\n'
<property> ::= <string>
<window> ::= any | root | <required property>
<required property> ::= <property/rp> | <property with value>
<property with value> ::= <property/rpv> = <string/rv>
<perms> ::= [ <operation> | <action> | <space> ]*
<operation> ::= r | w | d
<action> ::= a | i | e
<string> ::= <dbl quoted string> | <single quoted string> | <unquoted string>
<dbl quoted string> ::= <space> " <not dquote>* " <space>
<single quoted string> ::= <space> ' <not squote>* ' <space>
<unquoted string> ::= <space> <not space>+ <space>
<space> ::= [ ' ' | '\t' ]*
Character sets:
<not newline> ::= any character except '\n'
<not dquote>  ::= any character except "
<not squote>  ::= any character except '
<not space>   ::= any character except those in <space>

The semantics associated with the above syntax are as follows.

<version line>, the first line in the file, specifies the file format version. If the server does not recognize the version <string/v>, it ignores the rest of the file. The version string for the file format described here is "version-1" .

Once past the <version line>, lines that do not match the above syntax are ignored.

<comment> lines are ignored.

<sitepolicy> lines are currently ignored. They are intended to specify the site policies used by the XC-QUERY-SECURITY-1 authorization method.

<access rule> lines specify how the server should react to untrusted client requests that affect the X Window property named <property/ar>. The rest of this section describes the interpretation of an <access rule>.

For an <access rule> to apply to a given instance of <property/ar>, <property/ar> must be on a window that is in the set of windows specified by <window>. If <window> is any, the rule applies to <property/ar> on any window. If <window> is root, the rule applies to <property/ar> only on root windows.

If <window> is <required property>, the following apply. If <required property> is a <property/rp>, the rule applies when the window also has that <property/rp>, regardless of its value. If <required property> is a <property with value>, <property/rpv> must also have the value specified by <string/rv>. In this case, the property must have type STRING and format 8, and should contain one or more null-terminated strings. If any of the strings match <string/rv>, the rule applies.

The definition of string matching is simple case-sensitive string comparison with one elaboration: the occurrence of the character '*' in <string/rv> is a wildcard meaning "any string." A <string/rv> can contain multiple wildcards anywhere in the string. For example, "x*" matches strings that begin with x, "*x" matches strings that end with x, "*x*" matches strings containing x, and "x*y*" matches strings that start with x and subsequently contain y.

There may be multiple <access rule> lines for a given <property/ar>. The rules are tested in the order that they appear in the file. The first rule that applies is used.

<perms> specify operations that untrusted clients may attempt, and the actions that the server should take in response to those operations.

<operation> can be r (read), w (write), or d (delete). The following table shows how X Protocol property requests map to these operations in the X.Org server implementation.

GetProperty	r, or r and d if delete = True
ChangeProperty	w
RotateProperties	r and w
DeleteProperty	d
ListProperties	none, untrusted clients can always list all properties

<action> can be a (allow), i (ignore), or e (error). Allow means execute the request as if it had been issued by a trusted client. Ignore means treat the request as a no-op. In the case of GetProperty, ignore means return an empty property value if the property exists, regardless of its actual value. Error means do not execute the request and return a BadAtom error with the atom set to the property name. Error is the default action for all properties, including those not listed in the security policy file.

An <action> applies to all <operation>s that follow it, until the next <action> is encountered. Thus, irwad means ignore read and write, allow delete.

GetProperty and RotateProperties may do multiple operations (r and d, or r and w). If different actions apply to the operations, the most severe action is applied to the whole request; there is no partial request execution. The severity ordering is: allow < ignore < error. Thus, if the <perms> for a property are ired (ignore read, error delete), and an untrusted client attempts GetProperty on that property with delete = True, an error is returned, but the property value is not. Similarly, if any of the properties in a RotateProperties do not allow both read and write, an error is returned without changing any property values.

Here is an example security policy file.

version-1
# Allow reading of application resources, but not writing.
property RESOURCE_MANAGER	root	ar iw
property SCREEN_RESOURCES	root	ar iw
# Ignore attempts to use cut buffers.  Giving errors causes apps to crash,
# and allowing access may give away too much information.
property CUT_BUFFER0	root	irw
property CUT_BUFFER1	root	irw
property CUT_BUFFER2	root	irw
property CUT_BUFFER3	root	irw
property CUT_BUFFER4	root	irw
property CUT_BUFFER5	root	irw
property CUT_BUFFER6	root	irw
property CUT_BUFFER7	root	irw
# If you are using Motif, you probably want these.
property _MOTIF_DEFAULT_BINDINGS	root	ar iw
property _MOTIF_DRAG_WINDOW	root	ar iw
property _MOTIF_DRAG_TARGETS	any 	ar iw
property _MOTIF_DRAG_ATOMS	any 	ar iw
property _MOTIF_DRAG_ATOM_PAIRS	any 	ar iw
# The next two rules let xwininfo -tree work when untrusted.
property WM_NAME	any	ar
# Allow read of WM_CLASS, but only for windows with WM_NAME.
# This might be more restrictive than necessary, but demonstrates
# the <required property> facility, and is also an attempt to
# say "top level windows only."
property WM_CLASS	WM_NAME	ar
# These next three let xlsclients work untrusted.  Think carefully
# before including these; giving away the client machine name and command
# may be exposing too much.
property WM_STATE	WM_NAME	ar
property WM_CLIENT_MACHINE	WM_NAME	ar
property WM_COMMAND	WM_NAME	ar
# To let untrusted clients use the standard colormaps created by
# xstdcmap, include these lines.
property RGB_DEFAULT_MAP	root	ar
property RGB_BEST_MAP	root	ar
property RGB_RED_MAP	root	ar
property RGB_GREEN_MAP	root	ar
property RGB_BLUE_MAP	root	ar
property RGB_GRAY_MAP	root	ar
# To let untrusted clients use the color management database created
# by xcmsdb, include these lines.
property XDCCC_LINEAR_RGB_CORRECTION	root	ar
property XDCCC_LINEAR_RGB_MATRICES	root	ar
property XDCCC_GRAY_SCREENWHITEPOINT	root	ar
property XDCCC_GRAY_CORRECTION	root	ar
# To let untrusted clients use the overlay visuals that many vendors
# support, include this line.
property SERVER_OVERLAY_VISUALS	root	ar
# Dumb examples to show other capabilities.
# oddball property names and explicit specification of error conditions
property "property with spaces"	'property with "'	aw er ed
# Allow deletion of Woo-Hoo if window also has property OhBoy with value
# ending in "son".  Reads and writes will cause an error.
property Woo-Hoo	OhBoy = "*son"	ad

FILES

/usr/lib/xserver/SecurityPolicy
    Default X server security policy

SEE ALSO

Xserver(1), Security Extension Specification