runtime: don't execute external commands when loading ftplugins

This is a followup to 816fbcc262687b81fc46f82f7bbeb1453addfe0c (patch
9.0.1833: [security] runtime file fixes)

It basically disables that external commands are run on loading of the
filetype plugin, **unless** the user has set the `g:plugin_exec = 1`
global variable in their configuration or for a specific filetype the
variable g:<filetype>_exec=1.

There are a few more plugins, that may execute system commands like
debchangelog, gitcommit, sh, racket, zsh, ps1 but those do at least
do not run those commands by default during loading of the filetype plugin
(there the command is mostly run as convenience for auto-completion or
to provide documentation lookup).

closes: #13034

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Tim Pope <vim@tpope.org>

runtime/doc/filetype.txt

@@ -1,4 +1,4 @@
-*filetype.txt*  For Vim version 9.0.  Last change: 2023 Apr 29
+*filetype.txt*  For Vim version 9.0.  Last change: 2023 Sep 06
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -419,11 +419,24 @@ ways to change this:
 3.  Docs for the default filetype plugins.		*ftplugin-docs*
 
 
+					*plugin_exec* *g:plugin_exec*
+Enable executing of external commands.  This was done historically for e.g.
+the perl filetype plugin (and a few others) to set the search path.
+Disabled by default for security reasons: >
+	:let g:plugin_exec = 1
+It is also possible to enable this only for certain filetypes: >
+	:let g:<filetype>_exec = 1
+So to enable this only for ruby, set the following variable: >
+	:let g:ruby_exec = 1
+
+If both, the global `plugin_exec` and the `<filetype>_exec` specific variable
+are set, the filetpe specific variable should have precedent.
+
 AWK							*ft-awk-plugin*
 
 Support for features specific to GNU Awk, like @include, can be enabled by
 setting: >
-	let g:awk_is_gawk = 1
+	:let g:awk_is_gawk = 1
 
 
 CHANGELOG						*ft-changelog-plugin*

runtime/ftplugin/awk.vim

@@ -37,11 +37,14 @@ if exists("g:awk_is_gawk")
     let b:undo_ftplugin .= " | setl fp<"
   endif
 
-  let path = system("gawk 'BEGIN { printf ENVIRON[\"AWKPATH\"] }'")
-  let path = substitute(path, '^\.\=:\|:\.\=$\|:\.\=:', ',,', 'g') " POSIX cwd
-  let path = substitute(path, ':', ',', 'g')
+  " Disabled by default for security reasons.  
+  if get(g:, 'awk_exec', get(g:, 'plugin_exec', 0))
+    let path = system("gawk 'BEGIN { printf ENVIRON[\"AWKPATH\"] }'")
+    let path = substitute(path, '^\.\=:\|:\.\=$\|:\.\=:', ',,', 'g') " POSIX cwd
+    let path = substitute(path, ':', ',', 'g')
 
-  let &l:path = path
+    let &l:path = path
+  endif
   let b:undo_ftplugin .= " | setl inc< path<"
 endif
 

runtime/ftplugin/changelog.vim

@@ -55,13 +55,19 @@ if &filetype == 'changelog'
     elseif $EMAIL_ADDRESS != ""
       return $EMAIL_ADDRESS
     endif
+    let s:default_login = 'unknown'
 
-    let login = s:login()
+    " Disabled by default for security reasons.  
+    if get(g:, 'changelog_exec', get(g:, 'plugin_exec', 0))
+      let login = s:login()
+    else
+      let login = s:default_login
+    endif
     return printf('%s <%s@%s>', s:name(login), login, s:hostname())
   endfunction
 
   function! s:login()
-    return s:trimmed_system_with_default('whoami', 'unknown')
+    return s:trimmed_system_with_default('whoami', s:default_login)
   endfunction
 
   function! s:trimmed_system_with_default(command, default)
@@ -71,7 +77,7 @@ if &filetype == 'changelog'
   function! s:system_with_default(command, default)
     let output = system(a:command)
     if v:shell_error
-      return default
+      return a:default
     endif
     return output
   endfunction

runtime/ftplugin/perl.vim

@@ -54,10 +54,12 @@ endif
 
 " Set this once, globally.
 if !exists("perlpath")
-    " safety check: don't execute perl from current directory
     let s:tmp_cwd = getcwd()
-    if executable("perl") && (fnamemodify(exepath("perl"), ":p:h") != s:tmp_cwd
-          \ || (index(split($PATH,has("win32")? ';' : ':'), s:tmp_cwd) != -1 && s:tmp_cwd != '.'))
+    " safety check: don't execute perl binary by default
+    if executable("perl") && get(g:, 'perl_exec', get(g:, 'plugin_exec', 0))
+        \ && (fnamemodify(exepath("perl"), ":p:h") != s:tmp_cwd
+        \ || (index(split($PATH, has("win32") ? ';' : ':'), s:tmp_cwd) != -1
+        \ && s:tmp_cwd != '.'))
       try
 	if &shellxquote != '"'
 	    let perlpath = system('perl -e "print join(q/,/,@INC)"')
@@ -73,7 +75,7 @@ if !exists("perlpath")
 	" current directory and the directory of the current file.
 	let perlpath = ".,,"
     endif
-    unlet s:tmp_cwd
+    unlet! s:tmp_cwd
 endif
 
 " Append perlpath to the existing path value, if it is set.  Since we don't

runtime/ftplugin/ruby.vim

@@ -61,6 +61,10 @@ if !exists('g:ruby_version_paths')
 endif
 
 function! s:query_path(root) abort
+  " Disabled by default for security reasons.  
+  if !get(g:, 'ruby_exec', get(g:, 'plugin_exec', 0))
+    return []
+  endif
   let code = "print $:.join %q{,}"
   if &shell =~# 'sh' && empty(&shellxquote)
     let prefix = 'env PATH='.shellescape($PATH).' '
@@ -84,7 +88,7 @@ function! s:query_path(root) abort
     else
       let path = split(system(path_check),',')
     endif
-    unlet s:tmp_cwd
+    unlet! s:tmp_cwd
     exe cd cwd
     return path
   finally

runtime/ftplugin/zig.vim

@@ -40,17 +40,17 @@ endif
 let &l:define='\v(<fn>|<const>|<var>|^\s*\#\s*define)'
 
 " Safety check: don't execute zip from current directory
-let s:tmp_cwd = getcwd()
 if !exists('g:zig_std_dir') && exists('*json_decode') &&
-    \  executable('zig') && (fnamemodify(exepath("zig"), ":p:h") != s:tmp_cwd
-          \ || (index(split($PATH,has("win32")? ';' : ':'), s:tmp_cwd) != -1 && s:tmp_cwd != '.'))
+    \  executable('zig') && get(g:, 'zig_exec', get(g:, 'plugin_exec', 0))
+    \ && (fnamemodify(exepath("zig"), ":p:h") != s:tmp_cwd
+    \ || (index(split($PATH,has("win32")? ';' : ':'), s:tmp_cwd) != -1 && s:tmp_cwd != '.'))
     silent let s:env = system('zig env')
     if v:shell_error == 0
         let g:zig_std_dir = json_decode(s:env)['std_dir']
     endif
     unlet! s:env
 endif
-unlet s:tmp_cwd
+unlet! s:tmp_cwd
 
 if exists('g:zig_std_dir')
     let &l:path = &l:path . ',' . g:zig_std_dir