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session: Validate the token for correctness #1562

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session: Validate the token for correctness #1562

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23 changes: 23 additions & 0 deletions src/xdp-session.c
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Original file line number Diff line number Diff line change
Expand Up @@ -311,6 +311,20 @@ xdp_session_authorize_callback (GDBusInterfaceSkeleton *interface,
return TRUE;
}

static gboolean
is_valid_token(const char *token)
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Suggested change
is_valid_token(const char *token)
is_valid_token (const char *token)

{
int i;

for (i = 0; token[i]; i++)
{
if (!g_ascii_isalnum(token[i]) && token[i] != '_')
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Is _ a valid token? Doesn't gdbus already provide something like this?

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@smcv smcv Jan 10, 2025 •
edited
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If this is being used in object paths, https://dbus.freedesktop.org/doc/dbus-specification.html#message-protocol-names https://dbus.freedesktop.org/doc/dbus-specification.html#message-protocol-marshaling-object-path is the canonical specification.

gdbus probably doesn't have a function for "is this a valid object-path element?", though, just "is this a valid complete object path?" (which is g_variant_is_object_path()).

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@smcv smcv Jan 10, 2025 •
edited
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You could validate that the result of g_strdup_printf ("/foo/%s", token) is a valid object path, which I think is what we actually require. That's pretty ugly, but is it less ugly than open-coding validation? I don't know.

g_dbus_is_member_name() is almost right, but member names are not allowed to start with digits, whereas object path elements are, so using that would be unnecessarily restrictive.

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Is _ a valid token?

If our only functional requirement is "can we append it to /blah/blah/ and get a valid object path?" then yes it is.

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Suggested change
if (!g_ascii_isalnum(token[i]) && token[i] != '_')
if (!g_ascii_isalnum (token[i]) && token[i] != '_')

return FALSE;
}

return TRUE;
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This implementation would return true for the empty string, but "/blah/blah/" + "" is not a syntactically valid object path (an object path must not end with / unless it is exactly /). So we must check for that.

(We are probably appending it to some string in the /org/freedesktop/... namespace rather than literally /foo/ or /blah/blah/, but it's the "shape" that matters.)

}

static gboolean
xdp_session_initable_init (GInitable *initable,
GCancellable *cancellable,
Expand All @@ -335,6 +349,15 @@ xdp_session_initable_init (GInitable *initable,
return FALSE;
}

if (!is_valid_token(session->token))
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Suggested change
if (!is_valid_token(session->token))
if (!is_valid_token (session->token))

{
g_set_error (error,
XDG_DESKTOP_PORTAL_ERROR,
XDG_DESKTOP_PORTAL_ERROR_INVALID_ARGUMENT,
"Invalid token '%s'", session->token);
return FALSE;
}

id = g_strdup_printf ("/org/freedesktop/portal/desktop/session/%s/%s",
sender_escaped, session->token);

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13 changes: 13 additions & 0 deletions tests/test_remotedesktop.py
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Expand Up @@ -46,6 +46,19 @@ def test_remote_desktop_create_close_session(self, portals, dbus_con):
session.close()
xdp.wait_for(lambda: session.closed)

def test_remote_desktop_create_session_invalid(self, portals, dbus_con):
remotedesktop_intf = xdp.get_portal_iface(dbus_con, "RemoteDesktop")

request = xdp.Request(dbus_con, remotedesktop_intf)
options = {"session_handle_token": "Invalid-token&"}
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Please can we specifically test "/foo" and "" here, too? Those are special cases would be easy to get wrong.

for badness in ("Invalid-token&", "/foo", ""):
    options = { "session_handle_token": badness }

    with pytest.raises (etc.)
    ...


with pytest.raises(dbus.exceptions.DBusException) as excinfo:
request.call("CreateSession", options=options)
Comment on lines +55 to +56
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ohh, that's nice


e = excinfo.value
assert e.get_dbus_name() == "org.freedesktop.portal.Error.InvalidArgument"
assert "Invalid token" in e.get_dbus_message()

@pytest.mark.parametrize(
"template_params", ({"remotedesktop": {"force-close": 500}},)
)
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