Re: [RFC PATCH v1 0/5] Add support for O_MAYEXEC

From: Matthew Wilcox
Date: Thu Dec 13 2018 - 07:16:51 EST

On Thu, Dec 13, 2018 at 06:04:20AM -0500, Mimi Zohar wrote:
> > I don't have a problem with the concept, but we're running low on O_ bits.
> > Does this have to be done before the process gets a file descriptor,
> > or could we have a new syscall? Since we're going to be changing the
> > interpreters anyway, it doesn't seem like too much of an imposition to
> > ask them to use:
> >
> > int verify_for_exec(int fd)
> >
> > instead of adding an O_MAYEXEC.
> The indication needs to be set during file open, before the open
> returns to the caller.  This is the point where ima_file_check()
> verifies the file's signature.  On failure, access to the file is
> denied.

I understand that's what happens today, but do we need to do it that way?
There's no harm in the interpreter having an fd to a file if it knows
not to execute it. This is different from a program opening a file and
having the LSM deny access to it because it violates the security model.