Hi, Yes, it seems that there's a case that's missing, but I think not from regress/multipubkey.sh, because in this case there is only one public key, which is in ~/.ssh/id_dsa and in the agent I try to describe it: Topology: ------------- 1) client: OpenSSH 7.1p2 with running ssh-agent the client uses ssh-agent, and there is a passphrase-protected (e.g. DSA) key, that's loaded into the agent, but can be accessed via its standard file name (~/.ssh/id_dsa in the example). No more public key is available either in the agent or in ~/.ssh ssh -vp 2222 -o PubkeyAcceptedKeyTypes=+ssh-dss localhost -l gu=a@panther 2) the server: OpenSSH, but it doesn't really matter 3) between the client and the server there is a proxy that requires additional authentication not related to the server's authentication Communication without the patch, with output of 'ssh -v' -------------------------------------------------------------------------------- debug1: SSH2_MSG_SERVICE_ACCEPT received debug1: Authentications that can continue: publickey,keyboard-interactive 1) client sends that public key to the proxy without signature. (SSH_MSG_USERAUTH_REQUEST) debug1: Next authentication method: publickey debug1: Offering DSA public key: /home/panther/.ssh/id_dsa 2) the proxy accepts it, but requres the signed one (SSH_MSG_USERAUTH_PK_OK) debug1: Server accepts key: pkalg ssh-dss blen 434 3) client sends the public key with signature (USERAUTH_REQUEST) Here comes the tricky part, because the client already sent the public key, therefore it won't resend it: 4) the proxy tries this public key on the server side (USERAUTH_REQUEST, to the server, without signature) 5) the server doesn't know this key - missing from authorized_keys (USERAUTH_FAILURE, partial_succes=0) 6) the proxy sends this failure to the client (USERAUTH_FAILURE, partial_success=1 because it is alredy authenticated to the proxy) Authenticated with partial success debug1: Authentications that can continue: publickey,password >From now on the proxy doesn't really matter, just forwards packets: 7) the client retries the same public key from the agent (USERAUTH_REQUEST, without signature) debug1: Next authentication method: publickey debug1: Offering DSA public key: /home/panther/.ssh/id_dsa 8) the server receives this, and rejects it again (USERAUTH_FAILURE, partial_succes=0) Here the client goes wrong, I think: 9) the client is confused, finds the same public key, but not in the agent, therefore it tries to read from the file system, but it's encrypted debug1: Authentications that can continue: publickey,password debug1: Trying private key: /home/panther/.ssh/id_rsa debug1: Trying private key: /home/panther/.ssh/id_dsa Enter passphrase for key '/home/panther/.ssh/id_dsa': 10) I presss enter, and it falls back to password debug1: Trying private key: /home/panther/.ssh/id_ecdsa debug1: Trying private key: /home/panther/.ssh/id_ed25519 debug1: Next authentication method: password ....panther@localhost's password: Communication with the patch, with output of 'ssh -v' -------------------------------------------------------------------------------- 1-8) the same 9) the password method immediately (as it should be) debug1: Authentications that can continue: publickey,password debug1: Trying private key: /home/panther/.ssh/id_rsa debug1: Trying private key: /home/panther/.ssh/id_ecdsa debug1: Trying private key: /home/panther/.ssh/id_ed25519 debug1: Next authentication method: password ...panther@localhost's password: Shortly from the client's view, with step numbers: ---------------------------------------------------------------------- -1) USERATUH_REQUEST(none) 0) USERAUTH_FAILURE(publickey,keyboard-interactive, partial_success=0) 1) USERAUTH_REQUEST(publickey, no signature) 2) USERAUTH_PK_OK 3) USERAUTH_REQUEST(publickey, signature) 6) USERAUTH_FAILURE(publickey,password, partial_success=1) 7) USERAUTH_REQUEST(publickey, no signature) 8) USERAUTH_FAILURE(publickey,password, partial_success=0) and here the ~/.ssh/id_dsa file is read directly if OpenSSH is not patched Regards, Laszlo Attila Toth 2016-02-18 23:47 GMT+01:00 Damien Miller <djm@xxxxxxxxxxx>: > On Thu, 18 Feb 2016, Tóth, László Attila wrote: > > > Hi, > > > > I created a patch on the top of git repository git:// > > anongit.mindrot.org/openssh.git > > commit 292a8dee14e5e67dcd1b49ba5c7b9023e8420d59 djm@xxxxxxxxxxx upstream > > commit > > > > which fixes the issue, and OpenSSH client seems to be working fine in > this > > case, too. The patch is attached. > > I'm not exactly clear on what the problem is here - authentication using > multiple public keys is tested in the regress/multipubkey.sh test at the > moment. Is there a case that is missing? > > -d _______________________________________________ openssh-unix-dev mailing list openssh-unix-dev@xxxxxxxxxxx https://lists.mindrot.org/mailman/listinfo/openssh-unix-dev
