Fw: [Bug 105091] New: ICMP unreachable is not sent when receiving GRE packets on device that has no tunnel interface

Begin forwarded message:

Date: Sun, 27 Sep 2015 22:42:34 +0000
From: "bugzilla-daemon@bugzilla.kernel.org" <redacted>
To: "shemminger@linux-foundation.org" <redacted>
Subject: [Bug 105091] New: ICMP unreachable is not sent when receiving GRE packets on device that has no tunnel interface


https://bugzilla.kernel.org/show_bug.cgi?id=105091

            Bug ID: 105091
           Summary: ICMP unreachable is not sent when receiving GRE
                    packets on device that has no tunnel interface
           Product: Networking
           Version: 2.5
    Kernel Version: 4.2
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: low
          Priority: P1
         Component: IPV4
          Assignee: shemminger@linux-foundation.org
          Reporter: isaac.lee@alliedtelesis.co.nz
        Regression: No

Created attachment 188691
  --> https://bugzilla.kernel.org/attachment.cgi?id=188691&action=edit
fix patch

This used to work in version 3.9. In file ip_gre.c, when a GRE packet is
received and tunnel lookup returned NULL (ie, no such interface), ipgre_rcv()
calls icmp_send() to respond with port unreachable message.

In the latest version, gre_demux.c tries to do the same thing in
gre_cisco_rcv(), but icmp_send fails because skb dst entry has been dropped
(during parse_gre_header() -> iptunnel_pull_header() ->  skb_dst_drop(skb);)
prior to calling icmp_send, causing icmp_send to return early due to rt is
NULL.

A fix patch is attached.

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