This change drains unused SSH channels and requests to prevent a
situation where an attacker could repeatedly open channels and
send data that won't be read, causing Teleport to eventually run
out of memory.
* lazily forward SSH agents when connecting to agentless nodes
When connecting to unregistered OpenSSH nodes, the SSH agent is always
forwarded. When connecting to registered OpenSSH (agentless) nodes
however, the SSH agent doesn't *need* to be forwarded, so only do so
if the user explicitly asks to.
* test SSH agent forwarding in agentless integration test
To prevent users from being able to directly connect to registered
OpenSSH (Agentless) nodes, the OpenSSH CA was introduced. When
connecting to Agentless nodes, the Proxy will forward the connection
so the session can be recorded. The forwarding SSH server is configured
to authenticate to the target node with a certificate signed by OpenSSH
CA, which users do not have access to.
Proxy mode requires SSH agent forwarding permissions to work properly.
This tweaks the error message to mention that in a more direct manner.
Previous message:
$ tsh ssh mynode
> ERROR: failed connecting to node mynode. agent forwarding not requested or not authorized
New message:
$ tsh ssh mynode
> ERROR: failed connecting to node mynode. agent forwarding required in proxy recording mode
Adds support for Concurrent Session Control and a new
semaphore API. Roles now support two new configuration
options, `max_ssh_connections` and `max_ssh_sessions`
which correspond to the total number of authenticated
ssh connections per cluster, and the number of ssh sessions
within a connection respectively. Attempting to exceed
these limits generate variants of the `session.rejected`
audit event and cause the connection/session to be
rejected.
Changes agent channel setup behavior to be consistent
openssh by having servers lazily request agent channels
when they are needed, rather than immediately starting a
single connection-wide channel as soon as forwarding is
requested. Fixes an issue introduced in #3613 which
caused openssh clients to hang on exit due to persistent
agent channel.
Changes the lifetime of agent forwarding to be scoped
to the underlying ssh connection, instead of the
specific ssh channel which initially passed the agent
forwarding request.
Andrew Burke