SSH library vulnerabilities

After a channel is established, a malicious peer could send crafted messages causing a deadlock of the entire connection. Now all RFC 4254 channel messages are handled, and global requests are explicitly processed. Other messages are treated as protocol errors and the connection is torn down instead of buffering and blocking.

When writing data larger than 4GB in a single Write call on an SSH channel, an integer overflow in the internal payload size calculation caused an infinite loop sending empty packets. The fix uses int64 for size comparison to prevent truncation.

In an SSH library (likely Go), a malicious SSH peer can send unsolicited global request responses to fill an internal buffer, blocking the connection's read loop. The blocked goroutine cannot be released by calling Close(), resulting in a resource leak per connection. Unsolicited global responses are now discarded.