DOS-style socket paths are too permissive

[cuviper]

$ ssh-pageant -a "$(cygpath -w /tmp/foo)" sh -c 'ls -l $SSH_AUTH_SOCK'
srw-r--r-- 1 jistone None 0 Nov 16 14:22 C:\cygwin64\tmp\foo

Note that both group and other have read access, despite the internal umask 0177 used when binding the socket path. I hoped for a moment that other users still couldn't send requests to the agent without write access, but unfortunately they can!

This is a semi-intentional "feature" since cygwin 1.7.2, “Handle native DOS paths always as if mounted with "posix=0,noacl".” Without ACLs, umask and chmod are ineffective. At least Windows machines are usually single-user...

I think this can be fixed by using cygwin_conv_path to posix before binding.

[cuviper]

In a brief test with MSYS, it seems to always ignore umask and chmod, no matter what style of path is used, so I don't think that one can be fixed. The default /tmp path appears to be $LOCALAPPDATA though, which should be private at the Windows level.