/*
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * Copyright Tomi Manninen OH2BNS (oh2bns@sral.fi)
 */
#include <linux/types.h>
#include <linux/slab.h>
#include <linux/socket.h>
#include <linux/timer.h>
#include <net/ax25.h>
#include <linux/skbuff.h>
#include <net/netrom.h>
#include <linux/init.h>

static void nr_loopback_timer(unsigned long);

static struct sk_buff_head loopback_queue;
static DEFINE_TIMER(loopback_timer, nr_loopback_timer, 0, 0);

void __init nr_loopback_init(void)
{
	skb_queue_head_init(&loopback_queue);
}

static inline int nr_loopback_running(void)
{
	return timer_pending(&loopback_timer);
}

int nr_loopback_queue(struct sk_buff *skb)
{
	struct sk_buff *skbn;

	if ((skbn = alloc_skb(skb->len, GFP_ATOMIC)) != NULL) {
		skb_copy_from_linear_data(skb, skb_put(skbn, skb->len), skb->len);
		skb_reset_transport_header(skbn);

		skb_queue_tail(&loopback_queue, skbn);

		if (!nr_loopback_running())
			mod_timer(&loopback_timer, jiffies + 10);
	}

	kfree_skb(skb);
	return 1;
}

static void nr_loopback_timer(unsigned long param)
{
	struct sk_buff *skb;
	ax25_address *nr_dest;
	struct net_device *dev;

	if ((skb = skb_dequeue(&loopback_queue)) != NULL) {
		nr_dest = (ax25_address *)(skb->data + 7);

		dev = nr_dev_get(nr_dest);

		if (dev == NULL || nr_rx_frame(skb, dev) == 0)
			kfree_skb(skb);

		if (dev != NULL)
			dev_put(dev);

		if (!skb_queue_empty(&loopback_queue) && !nr_loopback_running())
			mod_timer(&loopback_timer, jiffies + 10);
	}
}

void __exit nr_loopback_clear(void)
{
	del_timer_sync(&loopback_timer);
	skb_queue_purge(&loopback_queue);
}
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<div class='path'>path: <a href='/cgit.cgi/linux/net-next.git/log/?id=be11f436a80b19cb5ef4cdfba7371a5178bd43cd&amp;showmsg=1'>root</a>/<a href='/cgit.cgi/linux/net-next.git/log/include?id=be11f436a80b19cb5ef4cdfba7371a5178bd43cd&amp;showmsg=1'>include</a>/<a href='/cgit.cgi/linux/net-next.git/log/include/net?id=be11f436a80b19cb5ef4cdfba7371a5178bd43cd&amp;showmsg=1'>net</a>/<a href='/cgit.cgi/linux/net-next.git/log/include/net/ipv6.h?id=be11f436a80b19cb5ef4cdfba7371a5178bd43cd&amp;showmsg=1'>ipv6.h</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/cgit.cgi/linux/net-next.git/log/include/net/ipv6.h?id=be11f436a80b19cb5ef4cdfba7371a5178bd43cd'>Collapse</a>)</th><th class='left'>Author</th><th class='left'>Files</th><th class='left'>Lines</th></tr>
<tr class='logheader'><td><span title='2017-01-31 13:16:59 -0500'>2017-01-31</span></td><td class='logsubject'><a href='/cgit.cgi/linux/net-next.git/commit/include/net/ipv6.h?id=90427ef5d2a4b9a24079889bf16afdcdaebc4240'>ipv6: fix flow labels when the traffic class is non-0</a></td><td>Dimitris Michailidis</td><td>1</td><td><span class='deletions'>-0</span>/<span class='insertions'>+5</span></td></tr>
<tr class='nohover-highlight'><td/><td colspan='5' class='logmsg'>
ip6_make_flowlabel() determines the flow label for IPv6 packets. It's
supposed to be passed a flow label, which it returns as is if non-0 and
in some other cases, otherwise it calculates a new value.

The problem is callers often pass a flowi6.flowlabel, which may also
contain traffic class bits. If the traffic class is non-0
ip6_make_flowlabel() mistakes the non-0 it gets as a flow label and
returns the whole thing. Thus it can return a 'flow label' longer than
20b and the low 20b of that is typically 0 resulting in packets with 0
label. Moreover, different packets of a flow may be labeled differently.
For a TCP flow with ECN non-payload and payload packets get different
labels as exemplified by this pair of consecutive packets:

(pure ACK)
Internet Protocol Version 6, Src: 2002:af5:11a3::, Dst: 2002:af5:11a2::
    0110 .... = Version: 6
    .... 0000 0000 .... .... .... .... .... = Traffic Class: 0x00 (DSCP: CS0, ECN: Not-ECT)
        .... 0000 00.. .... .... .... .... .... = Differentiated Services Codepoint: Default (0)
        .... .... ..00 .... .... .... .... .... = Explicit Congestion Notification: Not ECN-Capable Transport (0)
    .... .... .... 0001 1100 1110 0100 1001 = Flow Label: 0x1ce49
    Payload Length: 32
    Next Header: TCP (6)

(payload)
Internet Protocol Version 6, Src: 2002:af5:11a3::, Dst: 2002:af5:11a2::
    0110 .... = Version: 6
    .... 0000 0010 .... .... .... .... .... = Traffic Class: 0x02 (DSCP: CS0, ECN: ECT(0))
        .... 0000 00.. .... .... .... .... .... = Differentiated Services Codepoint: Default (0)
        .... .... ..10 .... .... .... .... .... = Explicit Congestion Notification: ECN-Capable Transport codepoint '10' (2)
    .... .... .... 0000 0000 0000 0000 0000 = Flow Label: 0x00000
    Payload Length: 688
    Next Header: TCP (6)

This patch allows ip6_make_flowlabel() to be passed more than just a
flow label and has it extract the part it really wants. This was simpler
than modifying the callers. With this patch packets like the above become

Internet Protocol Version 6, Src: 2002:af5:11a3::, Dst: 2002:af5:11a2::
    0110 .... = Version: 6
    .... 0000 0000 .... .... .... .... .... = Traffic Class: 0x00 (DSCP: CS0, ECN: Not-ECT)
        .... 0000 00.. .... .... .... .... .... = Differentiated Services Codepoint: Default (0)
        .... .... ..00 .... .... .... .... .... = Explicit Congestion Notification: Not ECN-Capable Transport (0)
    .... .... .... 1010 1111 1010 0101 1110 = Flow Label: 0xafa5e
    Payload Length: 32
    Next Header: TCP (6)

Internet Protocol Version 6, Src: 2002:af5:11a3::, Dst: 2002:af5:11a2::
    0110 .... = Version: 6
    .... 0000 0010 .... .... .... .... .... = Traffic Class: 0x02 (DSCP: CS0, ECN: ECT(0))
        .... 0000 00.. .... .... .... .... .... = Differentiated Services Codepoint: Default (0)
        .... .... ..10 .... .... .... .... .... = Explicit Congestion Notification: ECN-Capable Transport codepoint '10' (2)
    .... .... .... 1010 1111 1010 0101 1110 = Flow Label: 0xafa5e
    Payload Length: 688
    Next Header: TCP (6)

Signed-off-by: Dimitris Michailidis &lt;dmichail@google.com&gt;
Acked-by: Eric Dumazet &lt;edumazet@google.com&gt;
Signed-off-by: David S. Miller &lt;davem@davemloft.net&gt;


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