openssh unix dev - Oct 2004 - BUG: ssh-agent unlinks sockets/files it doesn't own.

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.

Rich wrote:
> 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.
Yes, I agree. Patch attached.
> 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.
I don't think it can easily tell if its socket has been unlinked. It is
probably unnecessary if 1 is done anyway.
> 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.
so would "rm -f /etc/passwd", so I think this falls into the case of
"don't do that" :)

-d
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