On Thu, Dec 08, 2016 at 10:32:00PM -0800, Cong Wang wrote:

quoted

Why do we do autobind there, anyway, and why is it conditional on
SOCK_PASSCRED?  Note that e.g. for SOCK_STREAM we can bloody well get
to sending stuff without autobind ever done - just use socketpair()
to create that sucker and we won't be going through the connect()
at all.

In the case Dmitry reported, unix_dgram_sendmsg() calls unix_autobind(),
not SOCK_STREAM.

Yes, I've noticed.  What I'm asking is what in there needs autobind triggered
on sendmsg and why doesn't the same need affect the SOCK_STREAM case?

I guess some lock, perhaps the u->bindlock could be dropped before
acquiring the next one (sb_writer), but I need to double check.

Bad idea, IMO - do you *want* autobind being able to come through while
bind(2) is busy with mknod?