safeArg: Little CLI util to pass null-delimited list of cmdline args to a program

Nick Sabalausky via Digitalmars-d-announce digitalmars-d-announce at puremagic.com
Mon Jun 8 23:16:11 PDT 2015


https://github.com/Abscissa/safeArg
http://code.dlang.org/packages/safearg

This is a small command line tool that was inspired by this: 
http://stackoverflow.com/questions/30720364/honoring-quoting-in-reading-shell-arguments-from-a-file

To quote safeArg's readme:

-----------------------------------------
Using eval or command substitution to pass arguments to a program is 
error-prone, non-portable and a potential security risk:

     Error-Prone: Proper shell quoting/escaping rules can be complex and 
confusing. Ignoring proper quoting/escaping can cause your program to 
fail (or worse) on certain inputs (such as filepaths with spaces, or 
multi-line data).

     Non-Portable: Posix platforms and Windows have completely different 
shells, and not all Windows machines have a Posix-style shell installed. 
Even the various Posix shells may have differences, and knowing whether 
you're relying on an extension-specific feature isn't always obvious.

     Potential Security Risk: Specially-constructed arguments can give 
an attacker full shell access.

A recommended solution is to use a null-delimited stream for sending the 
output of one command to the command line of another. This completely 
bypasses the shell's command parsing, and thus can avoid the problems 
above. Unfortunately, using the shell to actually send a null-delimited 
stream of arguments to a program can still be non-trivial and 
platform-specific, so this cross-platform tool helps you out:

$ safearg program_to_run < INPUT

For example (Granted, this example is using tools that aren't built-in 
on Windows, but it's only an example for illustration. Safearg itself is 
cross-platform, and sticking to only cross-platform tools would still 
work fine):

$ printf "[%s]\n" abc 'hello world'   # Let's try doing this
[abc]
[hello world]

$ echo abc \'hello world\' >datafile  # Store in file: abc 'hello world'
$ printf "[%s]\n" $(<datafile)        # Fails?! Plus, a security risk :(
[abc]
['hello]
[world']

$ echo -n '[%s]\n' >datafile          # Store printf's first arg
$ printf "\0abc\0hello world" >>datafile # Append next two args
$ safearg printf <datafile            # Works! And safe!
[abc]
[hello world]
-----------------------------------------

I think it's cool that this program is only about 100 LOC. Yay D :)


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