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mode. This addresses a well-known race condition that can cause servers to hang in accept(). The relevant case is when somebody connects to the server and then immediately kills the connection by sending a TCP reset. On the server this causes select to report a ready condition on the socket, after which the accept call blocks because there is no longer any pending connection to accept. In -current there is already a work-around for this in the kernel. It was merged into -stable some time ago, but then David Greenman reverted it because it seemed to be causing a socket leak in some cases. (See uipc_socket.c revision 1.51.2.3.) Hence this userland fix is needed in -stable, and I plan to merge it into that branch soon because it fixes a potential DoS attack. It may also be needed in -current if the suspected socket leak turns out to be real. In any case, after thinking it over I believe the fix belongs in userland. An application shouldn't assume that a ready return from select guarantees that the subsequent I/O operation cannot block. A lot can happen between the select and the accept. A similar fix should most likely be applied to the Unix domain socket transport too. Submitted by: peter Reviewed by: jdp
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