Introduction to redo

This article claims that redo suffers from several security issues at the very end. But can anyone explain to me how a userspace program that is run directly by the user can have any security issues at all? Also, apart from the PATH issue, all those "security holes" seem to require changing files, making them useless.

Besides, the author is wrong about the reasoning of apenwarr to implement #! processing[0]: it's done primarily to avoid having to make .do files executable. execlp() even executes /bin/sh all by itself if no header could be recognized[1]:

"If the header of a file isn't recognized (the attempted execve(2) failed with the error ENOEXEC), these functions will execute the shell (/bin/sh) with the path of the file as its first argument. (If this attempt fails, no further searching is done.)"

[0] https://github.com/apenwarr/redo#can-my-do-files-be-written-...

[1] http://linux.die.net/man/3/execv

Here is a great little video series that goes through implementing Redo in Haskell:

https://www.youtube.com/watch?v=zZ_nI9E9g0I