Re: [Libguestfs] [PATCH nbdkit v2] ssh: Improve the error message when all authentication methods fail

On 1/5/23 17:17, Richard W.M. Jones wrote: > The current error message: > > nbdkit: ssh[1]: error: all possible authentication methods failed > > is confusing and non-actionable. It's hard even for experts to > understand the relationship between the authentication methods offered > by a server and what we require. > > Try to improve the error message in some common situations, especially > where password authentication on the server side is disabled but the > client supplied a password=... parameter. After this change, you will > see an actionable error: > > nbdkit: ssh[1]: error: the server does not offer password > authentication but you tried to use a password; if you have root > access to the server, try editing 'sshd_config' and setting > 'PasswordAuthentication yes'; otherwise try setting up public key > authentication > > Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=2158300 > Thanks: Laszlo Ersek > --- > plugins/ssh/ssh.c | 22 ++++++++++++++++++++++ > 1 file changed, 22 insertions(+) > > diff --git a/plugins/ssh/ssh.c b/plugins/ssh/ssh.c > index aaa7c2b9f..5a132d8f2 100644 > --- a/plugins/ssh/ssh.c > +++ b/plugins/ssh/ssh.c > @@ -361,6 +361,28 @@ authenticate (struct ssh_handle *h) > if (rc == SSH_AUTH_SUCCESS) return 0; > } > > + /* All compatible methods were tried and none worked. Come up with > + * an actionable diagnostic message if we recognise the problem. > + */ > + if (!(method & SSH_AUTH_METHOD_PUBLICKEY) && password == NULL) { > + nbdkit_error ("the server does not offer public key authentication; " > + "try using the password=... parameter"); > + return -1; > + } > + if ((method & SSH_AUTH_METHOD_PASSWORD) && password != NULL) { > + nbdkit_error ("password authentication failed, " > + "is the username and password correct?"); > + return -1; > + } > + if (!(method & SSH_AUTH_METHOD_PASSWORD) && password != NULL) { > + nbdkit_error ("the server does not offer password authentication " > + "but you tried to use a password; if you have root access " > + "to the server, try editing 'sshd_config' and setting " > + "'PasswordAuthentication yes'; otherwise try setting up " > + "public key authentication"); > + return -1; > + } > + > nbdkit_error ("all possible authentication methods failed"); > return -1; > } Nice -- the auth logic is not changed, we're just checking various frequent problems, and providing matching hints. Now I wonder if the final error message remains reachable or not; but the nice thing about this approach is that we need not care! It doesn't really matter if we've covered *all* possible failures with helpful hints; the behavior remains safe, we just improve the user information in some known / frequent cases. Reviewed-by: Laszlo Ersek <lersek(a)redhat.com&gt;