ssh-keygen: error if file is directory

[Jim Knoble]

> On Jan 9, 2025, at 10:31, Bob Proulx <bob at proulx.com> wrote:
> 
> [...] In cases where
> something is checked and then later used there is a gap of time when
> the thing that was checked might be moved out of the way and replaced
> with a different thing before it is used.  That's a classic race
> condition attack. [...]

Thanks for calling that out, Bob.

This class of defect is sometimes referred to as [TOCTOU][*]. (The "Preventing TOCTOU" section talks about why the OpenSSH code is structured as it is: "EAFP").

[*]: https://en.m.wikipedia.org/wiki/Time-of-check_to_time-of-use

-- 
jim knoble