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    SubjectRe: [PATCH] ipv4: kernel panic when only one unsecured port available
    On Mon, 15 Oct 2007 13:06:14 -0700 (PDT)
    David Miller <davem@davemloft.net> wrote:

    > From: Andrew Morton <akpm@linux-foundation.org>
    > Date: Mon, 15 Oct 2007 12:49:19 -0700
    >
    > > This code has recently been reworked, but from my reading, that
    > > divide-by-zero can still occur. And given that the numbers in
    > > /proc/sys/net/ipv4/ip_local_port_range are inclusive, the arithmetic in
    > > inet_csk_get_port() seems to just be wrong?
    > >
    > > So we have this, against David's current devel tree:
    >
    > I'm pretty sure we took care of this, but maybe not :-)

    <looks>

    OK, in ipv4_local_port_range() we have

    if (range[1] <= range[0])
    ret = -EINVAL;

    which will prevent the crashes.

    But is it good to disallow high=low? This disallows a port range of one
    single port. Unless "high" is exclusive. But
    Documentation/filesystems/proc.txt says

    : ip_local_port_range
    : -------------------
    :
    : Range of ports used by TCP and UDP to choose the local port. Contains two
    : numbers, the first number is the lowest port, the second number the highest
    : local port. Default is 1024-4999. Should be changed to 32768-61000 for
    : high-usage systems.

    ie: inclusive.

    Documentation/networking/ip-sysctl.txt says

    : ip_local_port_range - 2 INTEGERS
    : Defines the local port range that is used by TCP and UDP to
    : choose the local port. The first number is the first, the
    : second the last local port number. Default value depends on
    : amount of memory available on the system:
    : > 128Mb 32768-61000
    : < 128Mb 1024-4999 or even less.
    : This number defines number of active connections, which this
    : system can issue simultaneously to systems not supporting
    : TCP extensions (timestamps). With tcp_tw_recycle enabled
    : (i.e. by default) range 1024-4999 is enough to issue up to
    : 2000 connections per second to systems supporting timestamps.

    also inclusive.


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