Re: Multiple Keys in ssh-agent, fail to clone

From: Junio C Hamano <gitster@pobox.com>
Date: Jul 13, 2016, 19:32 UTC
Message-ID: <xmqqziplz63l.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <CFA91608-1F29-4631-BABC-258404A62A3B@benle.de>

Benjamin Fritsch <beanie@benle.de> writes:

> I read the Changelog for 2.9 and couldn’t find any reference to changed key handling. Is there anything that I can add to the `git clone` command to get the old behavior?

I do not think this has much to do with the version of Git, unless you are getting an updated SSH client together with your new version of Git from whoever distributes it.

And it may not even be related to SSH version. Did you change your ~/.ssh/config recently by any chance? I personally do load many keys (one per destination) in the agent and back when I didn't know better, I didn't have IdentityFile line per each host, i.e. the last lines in these two entries were missing in my ~/.ssh/config:

    Host foo.bar.com
      Protocol 2
      User gitolite
      IdentityFile ~/.ssh/foo-bar-com

    Host foo.baz.com
      Protocol 2
      User junio
      IdentityFile ~/.ssh/foo-baz-com

If you try to do "ssh -v -v foo.bar.com" with such a configuration, you would observe that many keys are "offered" to the other side to see if it is the one that it recognises, and you end up offering too many of them before the right one. An output from such a failing session of "ssh -v" ends like this for me:

    $ ssh -v foo.bar.com
    ...
    debug1: Offering DSA public key: foo-baz-com
    debug1: Authentications that can continue: publickey
    debug1: Offering RSA public key: xxy-fsa-com
    debug1: Authentications that can continue: publickey
    debug1: Offering DSA public key: github
    debug1: Authentications that can continue: publickey
    debug1: ...
    debug1: Offering RSA public key: gitorious
    debug1: Authentications that can continue: publickey
    Received disconnect from 192.168.1.1: 2: Too many authentication failures for gitolite
    Disconnected from 192.168.1.1

If I do not have "IdentityFile ~/.ssh/foo-bar-com" line for the "Host foo.bar.com" part, "ssh -v foo.bar.com" cannot know which one of the keys it has available can be used to authenticate you with foo.bar.com, so it ends up asking "do you know this key and would you allow me to access you?" for each and every key. Having the line lets it use the appropriate key right at the beginning, would not leak (they are "public" keys, so "leak" is not that a serious problem, though) other public keys you have, and your authentication is likely to succeed.