"ssh-keygen -R hostname" errors out with non-existent known_hosts

[Nico Kadel-Garcia]

On Tue, Mar 23, 2021 at 7:01 PM Damien Miller <djm at mindrot.org> wrote:
>
> On Tue, 23 Mar 2021, Nico Kadel-Garcia wrote:
>
> > I've just run into what I consider a bug: If ~/.ssh/known_hosts does
> > not exist, and the account owner runs the command or their script
> > includes the command "ssh-keygen -R {hostname}", it reports an error
> > rather than reporting "oh, yes, the file was empty and therefore your
> > attempt to delete the hostname was unnecessary".
> >
> > If I want to delete a hostkey entry, and there is none to be found,
> > shouldn't that be considered a successful operation?
>
> I think the condition of known_hosts being absent is worth communicating.
> Maybe a different exit value for that case?

Exit 0, please. An absent known_hosts file doesn't contain the entry
the "ssh-keygen -R hostname" entry is expected to remove, and the
result should be considered a success for the command.

> diff --git a/ssh-keygen.c b/ssh-keygen.c
> index a442dc8e..3f603163 100644
> --- a/ssh-keygen.c
> +++ b/ssh-keygen.c
> @@ -1305,8 +1305,14 @@ do_known_hosts(struct passwd *pw, const char *name, int find_host,
>                 free(cp);
>                 have_identity = 1;
>         }
> -       if (stat(identity_file, &sb) != 0)
> -               fatal("Cannot stat %s: %s", identity_file, strerror(errno));
> +       if (stat(identity_file, &sb) != 0) {
> +               if (errno != ENOENT) {
> +                       fatal("Cannot stat %s: %s", identity_file,
> +                           strerror(errno));
> +               }
> +               logit("Hosts file %s does not exist", identity_file);
> +               cleanup_exit(1);
> +       }
>
>         memset(&ctx, 0, sizeof(ctx));
>         ctx.out = stdout;