Bug#759628: openssh-client: ssh ignores non-existent private key

[Ian Zimmerman <itz@buug.org>]

Package: openssh-client
Version: 1:6.6p1-4~bpo70+1
Severity: normal

I found that the following command

 ssh -i ~/.ssh/foo me@some.other.host

succeeds (with a warning) if ~/.ssh/foo doesn't exist or is otherwise
inaccessible, as long as the default private key can be used to connect
as specified.  I don't know if this can be abused, but I had a script
that kept "working" for months after I deleted the private key specified
because my default key happened to enable access.

IMO this should fail and not just warn.

-- System Information:
Debian Release: 7.6
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 3.10.53.3 (SMP w/4 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages openssh-client depends on:
ii  adduser           3.113+nmu3
ii  dpkg              1.16.15
ii  libc6             2.13-38+deb7u4
ii  libedit2          2.11-20080614-5
ii  libgssapi-krb5-2  1.10.1+dfsg-5+deb7u2
ii  libselinux1       2.1.9-5
ii  libssl1.0.0       1.0.1e-2+deb7u12
ii  passwd            1:4.1.5.1-1
ii  zlib1g            1:1.2.7.dfsg-13

Versions of packages openssh-client recommends:
ii  xauth  1:1.0.7-1

Versions of packages openssh-client suggests:
ii  keychain      2.7.1-1
pn  libpam-ssh    <none>
pn  monkeysphere  <none>
pn  ssh-askpass   <none>

-- Configuration Files:
/etc/ssh/ssh_config changed:
Host *
    SendEnv LANG LC_*
    HashKnownHosts no
    GSSAPIAuthentication yes
    GSSAPIDelegateCredentials no


-- no debconf information