openssh bugs - Jul 2017 - [Bug 2737] New: function identity_sign() assume private key's pub part as same as the .pub key.

https://bugzilla.mindrot.org/show_bug.cgi?id=2737

            Bug ID: 2737
           Summary: function identity_sign() assume private key's pub part
                    as same as the .pub key.
           Product: Portable OpenSSH
           Version: 7.5p1
          Hardware: Other
                OS: Other
            Status: NEW
          Severity: enhancement
          Priority: P5
         Component: ssh
          Assignee: unassigned-bugs at mindrot.org
          Reporter: jj.net at 163.com

1: we use 'ssh-keygen' create two  rsa pub/pri key pair with empty
passphrase.
and names it to:
<id_rsa1, id_rsa1.pub>
<id_rsa2, id_rsa2.pub>

2: add two pub key to localhost sshd:
cat id_rsa1.pub >> ~/.ssh/authorized_keys
cat id_rsa2.pub >> ~/.ssh/authorized_keys

3: copy the unmatch pub/pri key to ~/.ssh directory
cp id_rsa1 ~/.ssh/id_rsa
cp id_rsa2.pub ~/.ssh/id_rsa.pub

4: login to localhost without agent.
SSH_AUTH_SOCK= ssh 127.0.0.1 -vvv
can see ssh prompt user input password because of
method pubkey failed. the reasion is identity_sign() used
the id_rsa2.pub as pubkey, and signed it by id_rsa1 private key. that
sshd verify signature failed.

but, if you remove ~/.ssh/id_rsa.pub,
ssh client will used full ~/.ssh/id_rsa (extract pubkey,privatekey)
through
userauth_pubkey()
 -->sign_and_send_pubkey()
    -->identity_sign()
and login success.

i think ssh designed to login use pubkey as possible we you can.
and if id_rsa unmatch id_rsa.pub, ssh should trust id_rsa and drop the
rsa.pub file,  try do login again as id_rsa.pub not exist.

-- 
You are receiving this mail because:
You are watching the assignee of the bug.

https://bugzilla.mindrot.org/show_bug.cgi?id=2737

Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |djm at mindrot.org
             Blocks|                            |2698


Referenced Bugs:

https://bugzilla.mindrot.org/show_bug.cgi?id=2698
[Bug 2698] Tracking bug for OpenSSH 7.6 release
-- 
You are receiving this mail because:
You are watching someone on the CC list of the bug.
You are watching the assignee of the bug.

https://bugzilla.mindrot.org/show_bug.cgi?id=2737

Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |djm at mindrot.org
             Blocks|                            |2698

--- Comment #1 from Damien Miller <djm at mindrot.org> ---
I thought we checked that the public key matches the private, but I'll
take another look.


Referenced Bugs:

https://bugzilla.mindrot.org/show_bug.cgi?id=2698
[Bug 2698] Tracking bug for OpenSSH 7.6 release
-- 
You are receiving this mail because:
You are watching the assignee of the bug.
You are watching someone on the CC list of the bug.

https://bugzilla.mindrot.org/show_bug.cgi?id=2737

--- Comment #2 from jj.net at 163.com ---
i saw a comment 
'If the key is an certificate, try to find a matching private key....'
and key ssh-rsa is not certificate in keytypes.
so it skip private key match check in function sign_and_send_pubkey()
and maybe some reason i don't know to do this skip..

final the result is in ssh client's point of view, i have correct 
id_rsa keyfile but can't auto login, that is confusing.

-- 
You are receiving this mail because:
You are watching the assignee of the bug.
You are watching someone on the CC list of the bug.

https://bugzilla.mindrot.org/show_bug.cgi?id=2737

--- Comment #3 from Damien Miller <djm at mindrot.org> ---
Created attachment 3010
  --> https://bugzilla.mindrot.org/attachment.cgi?id=3010&action=edit
report mismatched private keys

I think this should catch the case of mismatched private and public
keys.

-- 
You are receiving this mail because:
You are watching the assignee of the bug.
You are watching someone on the CC list of the bug.

https://bugzilla.mindrot.org/show_bug.cgi?id=2737

--- Comment #4 from jj.net at 163.com ---
thanks, i apply this patch and it will report error if mismatched but
not try private again,  and add some code to fix it and works.

a/sshconnect2.c

ssherr.h
---------------
    #define SSH_ERR_CONN_CORRUPT               -54
    #define SSH_ERR_PROTOCOL_ERROR          -55
+  #define SSH_ERR_KEY_RETRY_PRIVATE       -56

    /* Translate a numeric error code to a human-readable error string
*/
   const char *ssh_err(int n);


ssherr.c
---------------
        case SSH_ERR_PROTOCOL_ERROR:
            return "Protocol error";
+       case SSH_ERR_KEY_RETRY_PRIVATE:
+           return "Key retry private";
        default:
            return "unknown error";

ssconnect2.c
---------------
        /* load the private key from the file */
        if ((prv = load_identity_file(id)) == NULL)
                return SSH_ERR_KEY_NOT_FOUND;
+       if (id->key != NULL && !sshkey_equal_public(prv, id->key))
{
+               error("%s: private key %s contents do not match public,
try again with private key",
+                  __func__, id->filename);
+               return SSH_ERR_KEY_RETRY_PRIVATE;
+       }
        ret = sshkey_sign(prv, sigp, lenp, data, datalen,
            key_sign_encode(prv), compat);
        sshkey_free(prv);
...
     ret = identity_sign(id, &signature, &slen,
         buffer_ptr(&b), buffer_len(&b), datafellows);
     if (ret != 0) {
         if (ret != SSH_ERR_KEY_NOT_FOUND)
             error("%s: signing failed: %s", __func__, ssh_err(ret));
+        if (ret == SSH_ERR_KEY_RETRY_PRIVATE) {
+           id->tried = 0;
+            key_free(id->key);
+            id->key = NULL;
+            TAILQ_REMOVE(&authctxt->keys, id, next);
+            TAILQ_INSERT_HEAD(&authctxt->keys, id, next);
         }
         free(blob);
         buffer_free(&b);

-- 
You are receiving this mail because:
You are watching the assignee of the bug.
You are watching someone on the CC list of the bug.

https://bugzilla.mindrot.org/show_bug.cgi?id=2737

--- Comment #5 from Damien Miller <djm at mindrot.org> ---
I'm reluctant to add more code here. I think it's sufficient to inform
the user and let them fix the configuration error if they desire.

(also, please use the attachments feature for patches in future.)

-- 
You are receiving this mail because:
You are watching the assignee of the bug.
You are watching someone on the CC list of the bug.

https://bugzilla.mindrot.org/show_bug.cgi?id=2737

Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Attachment #3010|0                           |1
        is obsolete|                            |
           Assignee|unassigned-bugs at mindrot.org |djm at mindrot.org
                 CC|                            |dtucker at zip.com.au
             Status|NEW                         |ASSIGNED
   Attachment #3021|                            |ok?(dtucker at zip.com.au)
              Flags|                            |

--- Comment #6 from Damien Miller <djm at mindrot.org> ---
Created attachment 3021
  --> https://bugzilla.mindrot.org/attachment.cgi?id=3021&action=edit
with better error code

This improves the error code returned when the keys don't match.

-- 
You are receiving this mail because:
You are watching the assignee of the bug.
You are watching someone on the CC list of the bug.

https://bugzilla.mindrot.org/show_bug.cgi?id=2737

Darren Tucker <dtucker at zip.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Attachment #3021|ok?(dtucker at zip.com.au)     |ok+
              Flags|                            |

-- 
You are receiving this mail because:
You are watching someone on the CC list of the bug.
You are watching the assignee of the bug.

https://bugzilla.mindrot.org/show_bug.cgi?id=2737

Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #7 from Damien Miller <djm at mindrot.org> ---
Patch is applied, this will be in openssh-7.6. Thanks!

-- 
You are receiving this mail because:
You are watching the assignee of the bug.
You are watching someone on the CC list of the bug.

https://bugzilla.mindrot.org/show_bug.cgi?id=2737

Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |carlpaten at gmail.com

--- Comment #8 from Damien Miller <djm at mindrot.org> ---
*** Bug 2776 has been marked as a duplicate of this bug. ***

-- 
You are receiving this mail because:
You are watching someone on the CC list of the bug.
You are watching the assignee of the bug.

https://bugzilla.mindrot.org/show_bug.cgi?id=2737

Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ilesterg at archlinux.info

--- Comment #9 from Damien Miller <djm at mindrot.org> ---
*** Bug 2661 has been marked as a duplicate of this bug. ***

-- 
You are receiving this mail because:
You are watching the assignee of the bug.
You are watching someone on the CC list of the bug.

https://bugzilla.mindrot.org/show_bug.cgi?id=2737

Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |CLOSED

--- Comment #10 from Damien Miller <djm at mindrot.org> ---
closing resolved bugs as of 8.6p1 release

-- 
You are receiving this mail because:
You are watching someone on the CC list of the bug.
You are watching the assignee of the bug.