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ModelineCommands : Extended modelines that allow the execution of arbitrary Vim commands.

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created by
Ingo Karkat
 
script type
utility
 
description
DESCRIPTION
Modelines are a comfortable means to adapt Vim settings (like filetype and
indentation), embedded in the edited file itself. For a power user, it would
be beneficial to apply the same concept to plugin settings and other
customizations. Unfortunately, modelines are not extensible, and cannot be
used to set variables or invoke other commands. One has to define |autocmd|s,
or use a local vimrc plugin, but those solutions all keep the configuration
separate from the edited file, so it's more effort to keep it in sync.

This plugin extends Vim's built-in modelines to execute any Ex command(s) when
a file is opened. A set of configurable validators examine the commands and
can verify the correctness of an optional command digest, in order to prevent
the execution of potentially malicious commands from unknown sources. This
way, you could restrict the commands to only simple :let, or have the plugin
query you to confirm execution of anything that isn't signed with your own
secret key.

SEE ALSO
- The localrc plugin (vimscript #3393), especially with my own enhancements
  (https://github.com/inkarkat/vim-localrc/tree/enhancements) executes Vim
  scripts in the same directory as the opened file, also based on filetype.
  With this, you can place arbitrary customizations close to the file(s), but
  still external to them.

RELATED WORKS
- let-modeline.vim (vimscript #83) extends the modeline feature to the
  assignment of variables

USAGE
Modeline commands are read and executed after the buffer has been read (i.e.
on BufReadPost). The first and last lines of the buffer are searched for
them.

The modeline command syntax is similar to the second form of the built-in
modeline feature, using the vimcommand: prefix instead of vim:
The command(s) (you can both concatenate multiple Ex commands via :bar
and/or have separate modeline commands on multiple lines) are concluded with a
":" (followed by an optional command digest for verification of its integrity,
also concluded with a ":"); that means that colons within the command must be
escaped by preceding them with a backslash.

    [text]{white}{vimcommand:|VimCommand:}[!][white]:{commands}:[text]
    [text]{white}{vimcommand:|VimCommand:}[!][white]:{commands}:[white]{digest}[white]:[text]

[text]                  any text or empty
{white}                 at least one blank character (<Space> or <Tab>)
{vimcommand:|VimCommand:}the string "vimcommand:" or "VimCommand:"
[!]                     optional marker for :silent! execution
[white]                 optional white space
{commands}              Ex commands
:[white]{digest}[white] optional hash over {commands} and
                        g:ModelineCommands_Secret concatenated together, to
                        verify the integrity of {commands}
:                       a colon
[text]                  any text or empty

EXAMPLE
The default g:ModelineCommands_CommandValidator only whitelists simple
:let variable assignments and :echomsg commands (to / of numbers and
String literals), to prevent the execution of potentially malicious commands.
   /* vimcommand: let b\:frobnize = "on": */
   /* vimcommand: echomsg "echoed from a modeline": */
The default validator actually is a sequence of the whitelist and an
interactive user query:
   /* vimcommand: source ~/.vim/additions.vim: */
As the last modeline is not whitelisted, the user is queried:
    ModelineCommands: Execute command?
    source ~/.vim/additions.vim
    (Y)es, (N)o, (A)lways, Ne(v)er, (F)orever, Never (e)ver:
If the user declines, the command is rejected:
    ModelineCommands: Command did not pass validation: source ~/.vim/additions.vim

To allow additional commands (without querying), you either have to:
- extend the whitelist in g:ModelineCommands_ValidCommandPattern
- disable the default validator
    :let g:ModelineCommands_CommandValidator = ''
which with the default policy in g:ModelineCommands_AcceptUnvalidated will
  ask you for confirmation (just like with the default validator)
- write your own custom validator; you can also chain multiple validators (so
  any acceptance greenlights the command); cp.
  ModelineCommands-CompositeCommandValidator
- use the g:ModelineDigests_DigestValidator that allows you to sign
  modelines with a secret key, and append that digest to the command:
   /* vimcommand: source ~/.vim/additions.vim:8e69fa01: */
   /* vimcommand: echomsg "modeline commands\: an example" | version:7fab292cd: */
 
install details
INSTALLATION
The code is hosted in a Git repo at
    https://github.com/inkarkat/vim-ModelineCommands
You can use your favorite plugin manager, or "git clone" into a directory used
for Vim packages. Releases are on the "stable" branch, the latest unstable
development snapshot on "master".

This script is also packaged as a vimball. If you have the "gunzip"
decompressor in your PATH, simply edit the *.vmb.gz package in Vim; otherwise,
decompress the archive first, e.g. using WinZip. Inside Vim, install by
sourcing the vimball or via the :UseVimball command.
    vim ModelineCommands*.vmb.gz
    :so %
To uninstall, use the :RmVimball command.

DEPENDENCIES
- Requires Vim 7.0 or higher.
- Requires the ingo-library.vim plugin (vimscript #4433), version 1.036 or
  higher.

CONFIGURATION
For a permanent configuration, put the following commands into your vimrc:

If you want to search for modeline commands only in certain files, you can
specify autocmd-patterns instead of the default "*". This must be set before
the plugin is sourced:
    let g:ModelineCommands_FilePattern = '*.h,*.c,*.cpp'

The number of lines at the start of the buffer that are searched for modeline
commands; the default is 'modelines'
    let g:ModelineCommands_FirstLines = 10

As arbitrary Vim commands can do harm to your system (with :! and :call
system(...), you can execute any external command!), there are two kinds of
gatekeepers:

COMMAND VALIDATION
Modeline commands that do not have a digest attached can be filtered based on
the command itself. You can configure a Funcref that takes the command as an
argument, and returns whether it should be allowed:
    let g:ModelineCommands_CommandValidator = function('...')
The validator probably will attempt to match the passed command with a regexp.
Note that blacklisting is unreliable, as there are many ways that malicious
commands can be written. Better just allow certain, harmless commands, and be
strict with your regular expression. The default validator first tries to
match the command with a single regular expression:

The default pattern just allows simple :let variable assignments and
:echomsg of literal numbers and strings. Note that depending on your plugins
and configuration, even that simple setting of variables can lead to
vulnerabilities!
If that fails, the user is queried. To drop that interactive part and simply
reject, replace the composite command validator with the whitelist one:
    let g:ModelineCommands_CommandValidator = function('ModelineCommands#Validators#ModelineCommands#Validators#RegexpCommandValidator')
You can also add custom validators into the chain:
    let g:ModelineCommands_CompositeCommandValidators = [function(...), ...]

DIGEST VALIDATION
This is used if the modeline command has a :{digest} appended.

Both the modeline command and the digest are passed to this validator. The
validator should re-generate the digest from the passed command and a secret,
and compare that with the passed digest. At least that's what the default
digest validator is doing, with a SHA-256 hash.

The format of the digest depends on the digest function, typically it is a
hexadecimal string. Vim's sha256() function returns a 64-digit hex number.
The default digest validator accepts shorter digests, so you can truncate the
long number in the modeline. How short (and therefore how insecure) the
digest may be can be configured in the digest pattern.
    let g:ModelineCommands_DigestPattern = '\x\{8,64}'

The default digest validator requires a secret string. Either put that
directly into the variable, or assign a Funcref that will return it. If a
person knows the secret, he can create valid digests for arbirary modeline
commands, and make you execute the command when you open the file, so guard
this secret carefully!

VALIDATION POLICY
Validation establishes a certain level of security. If it fails, the command
will be rejected. You can still configure the policy for accepted commands,
one of "no" (discarded), "ask" (query user before execution), "yes" (allow).

Policy for commands where no (command or digest-based) validator is configured:
    let g:ModelineCommands_AcceptUnvalidated = "ask"
Note: You need to disable the default validator(s) for this setting to take
effect.

Policy for commands that passed a (command or digest-based) validator:
    let g:ModelineCommands_AcceptValidated = "yes"

Those confirmations can be remembered for the current Vim session, and also
across sessions if the "!" flag is part of the 'viminfo' setting):
    set viminfo^=!  " Save and restore global variables.
 

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script versions (upload new version)

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package script version date Vim version user release notes
ModelineCommands-1.01.vmb.gz 1.01 2020-07-29 7.0 Ingo Karkat - ENH: Allow to persist the "ask" confirmation result also across Vim sessions.
- CHG: Install a composite command validator by default so that the user is queried for commands that are not whitelisted. With the extended persistence across sessions, the query mechanism may already work well enough for some users, and there's then no need to reconfigure the plugin. Also, a query is a better out-of-the-box behavior than rejecting modelines.
- CHG: Don't allow :let commands that modify the plugin's own configuration, as this could create vulnerabilities. *** You need to update to ingo-library (vimscript #4433) version 1.036! ***
ModelineCommands-1.00.vmb.gz 1.00 2019-01-18 7.0 Ingo Karkat Initial upload
ip used for rating: 34.234.223.162

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