From owner-cvs-all  Wed Nov 17 19: 1:11 1999
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From: John Polstra <jdp@FreeBSD.org>
Date: Wed, 17 Nov 1999 19:01:08 -0800 (PST)
To: cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org
Subject: cvs commit: src/lib/libc/rpc svc_tcp.c
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jdp         1999/11/17 19:01:08 PST

  Modified files:
    lib/libc/rpc         svc_tcp.c 
  Log:
  For the TCP transport, put the listening socket in non-blocking
  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
  
  Revision  Changes    Path
  1.16      +19 -1     src/lib/libc/rpc/svc_tcp.c



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