Security: remove support for $(...) in config keys with [$e] marker.

Summary:
It is very unclear at this point what a valid use case for this feature
would possibly be. The old documentation only mentions $(hostname) as
an example, which can be done with $HOSTNAME instead.

Note that $(...) is still supported in Exec lines of desktop files,
this does not require [$e] anyway (and actually works better without it,
otherwise the $ signs need to be doubled to obey kconfig $e escaping rules...).

Test Plan:
ctest passes; various testcases with $(...) in desktop files,
directory files, and config files, no longer execute commands.

Reviewers: mdawson, aacid, broulik, davidedmundson, kossebau, apol, sitter, security-team

Reviewed By: mdawson, davidedmundson

Subscribers: ZaWertun, rikmills, fvogt, ngraham, kde-frameworks-devel

Tags: #frameworks

Differential Revision: https://phabricator.kde.org/D22979

1 files changed, 4 insertions, 7 deletions

diff --git a/docs/options.md b/docs/options.md
index c634c000..4a6e9bc1 100644
--- a/docs/options.md
+++ b/docs/options.md
@@ -67,18 +67,15 @@ environment variables (and `XDG_CONFIG_HOME` in particular).
 Shell Expansion
 ---------------
 
-If an entry is marked with `$e`, environment variables and shell commands will
-be expanded.
+If an entry is marked with `$e`, environment variables will be expanded.
 
     Name[$e]=$USER
-    Host[$e]=$(hostname)
 
 When the "Name" entry is read `$USER` will be replaced with the value of the
-`$USER` environment variable, and `$(hostname)` will be replaced with the output
-of the `hostname` command.
+`$USER` environment variable.
 
-Note that the application will replace `$USER` and `$(hostname)` with their
-respective expanded values after saving. To prevent this combine the `$e` option
+Note that the application will replace `$USER` with its
+expanded value after saving. To prevent this combine the `$e` option
 with `$i` (immmutable) option.  For example:
 
     Name[$ei]=$USER