Safename: restricting “dangerous” file names | Hacker News Reader

Safename: restricting “dangerous” file names

lwn.net

15 pointssciurus7 comments

Restricting users because the software is buggy sounds like the wrong way to solve the problem.

Not to mention the error handling:

Any attempt to create a file name that fails the tests will be rejected with an EPERM error

So the user will get a "permission denied" error when trying to save a file instead of "the file name contained invalid characters, which are...".

Security isn't about solving problems the right way, it's about reducing attack surface.

The kernel system call interface has a fixed set of error codes to work with. EPERM is the most applicable one available.

This really ought to be table-driven so that custom tables can be loaded.

For example, what about Unicode normalization? It's enforced on OS X. Maybe I want to block anything that differs according to normalization form.

I might want to limit characters to 2 accents at most. (this covers Vietnamese)

I might want only left-to-right characters or LGC characters.

I might want to block confusing look-alike characters, particularly those the non-ASCII ones that look like ASCII.

I was thinking it would be neat if the filenames would be passed through a eBPF filter. That should cover almost all imaginable usecases.

   mkdir some-test
   cd some-test
   mkdir some-dir
   echo foo > some-dir/some-file
   echo bar > -Rf
   ls -l
   rm *
   ls -l

Bash script is a bad choice here.