BUG: ssh-agent unlinks sockets/files it doesn't own.

[Rich]

I've noticed a problem in the openssh sources.  It can most easily be
replicated as follows:


> [rich at goblin] sl=1 ~
> 01:05:47$ ssh-agent -a ~/.ssh/agent.sock 
> SSH_AUTH_SOCK=/home/rich/.ssh/agent.sock; export SSH_AUTH_SOCK;
> SSH_AGENT_PID=553; export SSH_AGENT_PID;
> echo Agent pid 553;
> 
> [rich at goblin] sl=1 ~
> 01:05:50$ ssh-agent -a ~/.ssh/agent.sock 
> bind: Address already in use
> 
> [rich at goblin] sl=1 ~
> 01:05:53$ ssh-agent -a ~/.ssh/agent.sock 
> SSH_AUTH_SOCK=/home/rich/.ssh/agent.sock; export SSH_AUTH_SOCK;
> SSH_AGENT_PID=558; export SSH_AGENT_PID;
> echo Agent pid 558;

The first ssh-agent survives the ordeal, but finds itself unreachable,
and without purpose.

I would suggest a couple of changes:

1)	unless bind has been successful, don't unlink the socket.
2)	teach ssh-agent to either die or rebind if his socket disappears.
	my pref would probably be death, as I find it more elegant than
	killing it with ssh-agent -k.

The first probably wise for good manners, even though the second will
solve the problem.  note that:

> su
> ssh-agent -a /etc/passwd

would probably have unpleasant repercussions.