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Bug 1687230 - When using ssh-agent with ecdsa-sha2-nistp384 key on a security key (Yubikey 5 NC in this case) ssh-agent fails to sign and then seg faults.
Summary: When using ssh-agent with ecdsa-sha2-nistp384 key on a security key (Yubikey ...
Alias: None
Product: Fedora
Classification: Fedora
Component: openssh
Version: 29
Hardware: x86_64
OS: Linux
Target Milestone: ---
Assignee: Jakub Jelen
QA Contact: Fedora Extras Quality Assurance
Depends On:
TreeView+ depends on / blocked
Reported: 2019-03-11 01:46 UTC by Nick Pope
Modified: 2019-03-11 12:47 UTC (History)
8 users (show)

Fixed In Version:
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Description Nick Pope 2019-03-11 01:46:15 UTC
Description of Problem:
When using ssh-agent with ecdsa-sha2-nistp384 key on a security key (Yubikey 5 NC in this case) ssh-agent fails to sign and then seg faults.  FWIW RSA keys on a security key work with ssh-agent.

How reproducible:

Steps to reproduce:
# Create ECDSA key
$ yubico-piv-tool -s 9a -AECCP384 -a generate -o public.pem --key
Enter management key: 
Successfully generated a new private key.
$ yubico-piv-tool -a verify-pin -a selfsign-certificate -s 9a -S "/CN=SSH key/" -i public.pem -o cert.pem
Enter PIN: 
Successfully verified PIN.
Successfully generated a new self signed certificate.
$ yubico-piv-tool -a import-certificate -s 9a -i cert.pem --key
Enter management key: 
Successfully imported a new certificate.
$ ssh-keygen -D /usr/lib64/ -e
ecdsa-sha2-nistp384 AAAAE2VjZHNhLXNoYTItbmlzdHAzODQAAAAIbmlzdHAzODQAAABhBIYBDDS9N+FlOyRviNzcg6RNGFU37MdSfgWFOWOvS/ge9BPl976rU27gvo/Vd+sIp7VHZYrVL8vidQ1pjb8DMr0lbSRnSFk6YPw4MPqEdPl0QLwzCBsR6niM2i4D2cm5EA==
# Copy the public key to localhost ~/.ssh/authorized_keys file
$ echo 'ecdsa-sha2-nistp384 AAAAE2VjZHNhLXNoYTItbmlzdHAzODQAAAAIbmlzdHAzODQAAABhBIYBDDS9N+FlOyRviNzcg6RNGFU37MdSfgWFOWOvS/ge9BPl976rU27gvo/Vd+sIp7VHZYrVL8vidQ1pjb8DMr0lbSRnSFk6YPw4MPqEdPl0QLwzCBsR6niM2i4D2cm5EA==' > ~/.ssh/authorized_keys
# Cleanup any currently running ssh-agent and start a ssh-agent in debug mode
$ pkill -9 ssh-agent; rm -rf /tmp/ssh-*; ssh-agent -D
SSH_AUTH_SOCK=/tmp/ssh-gbmJQM6y7tq8/agent.9141; export SSH_AUTH_SOCK;
echo Agent pid 9141;
# In another terminal add the SSH_AUTH_SOCK environment variable
$ SSH_AUTH_SOCK=/tmp/ssh-gbmJQM6y7tq8/agent.9141; export SSH_AUTH_SOCK;
$ ssh-add -s /usr/lib64/
Enter passphrase for PKCS#11: 
Card added: /usr/lib64/
$ ssh-add -L
ecdsa-sha2-nistp384 AAAAE2VjZHNhLXNoYTItbmlzdHAzODQAAAAIbmlzdHAzODQAAABhBIYBDDS9N+FlOyRviNzcg6RNGFU37MdSfgWFOWOvS/ge9BPl976rU27gvo/Vd+sIp7VHZYrVL8vidQ1pjb8DMr0lbSRnSFk6YPw4MPqEdPl0QLwzCBsR6niM2i4D2cm5EA== /usr/lib64/
$ ssh localhost
$ ssh localhost

Actual results:
$ ssh localhost
sign_and_send_pubkey: signing failed: agent refused operation
user@localhost: Permission denied (publickey,gssapi-keyex,gssapi-with-mic).
$ ssh localhost

Now notice in the ssh-agent debug output it failed to sign, and when we ran ssh localhost again ssh-agent seg faulted
echo Agent pid 9141;
process_sign_request2: sshkey_sign: error in libcrypto
Segmentation fault

Expected results:
Successfully authenticated against ssh server

Additional info:
$ cat /etc/fedora-release 
Fedora release 29 (Twenty Nine)
$ rpm -qa | grep -E 'ssh|opensc|yubico-piv'

Comment 1 Jakub Jelen 2019-03-11 09:57:22 UTC
It looks like I can reproduce the issue with my yubikey 4. The ssh-agent support is still a bit clunky (bug #1609055) and the upstream rewrote [1] the ECDSA support from scratch recently so it should land in the next release in coming weeks or few months. Given these constraints, I do not think it makes sense to fix it in the current code, but I will make sure it will work with the next upstream release. In the meantime, you should be able to use either RSA keys or ECDSA keys not through the agent.


Comment 2 Nick Pope 2019-03-11 12:47:13 UTC
Thanks for the quick confirmation.  I'll keep my eye on this bugzilla and retest when there is a relevant update in the Fedora repos.

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