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    Subject[PATCH 4.9 164/177] ip6_vti: adjust vti mtu according to mtu of lower device
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Alexey Kodanev <alexey.kodanev@oracle.com>


    [ Upstream commit 53c81e95df1793933f87748d36070a721f6cb287 ]

    LTP/udp6_ipsec_vti tests fail when sending large UDP datagrams over
    ip6_vti that require fragmentation and the underlying device has an
    MTU smaller than 1500 plus some extra space for headers. This happens
    because ip6_vti, by default, sets MTU to ETH_DATA_LEN and not updating
    it depending on a destination address or link parameter. Further
    attempts to send UDP packets may succeed because pmtu gets updated on
    ICMPV6_PKT_TOOBIG in vti6_err().

    In case the lower device has larger MTU size, e.g. 9000, ip6_vti works
    but not using the possible maximum size, output packets have 1500 limit.

    The above cases require manual MTU setup after ip6_vti creation. However
    ip_vti already updates MTU based on lower device with ip_tunnel_bind_dev().

    Here is the example when the lower device MTU is set to 9000:

    # ip a sh ltp_ns_veth2
    ltp_ns_veth2@if7: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9000 ...
    inet 10.0.0.2/24 scope global ltp_ns_veth2
    inet6 fd00::2/64 scope global

    # ip li add vti6 type vti6 local fd00::2 remote fd00::1
    # ip li show vti6
    vti6@NONE: <POINTOPOINT,NOARP> mtu 1500 ...
    link/tunnel6 fd00::2 peer fd00::1

    After the patch:
    # ip li add vti6 type vti6 local fd00::2 remote fd00::1
    # ip li show vti6
    vti6@NONE: <POINTOPOINT,NOARP> mtu 8832 ...
    link/tunnel6 fd00::2 peer fd00::1

    Reported-by: Petr Vorel <pvorel@suse.cz>
    Signed-off-by: Alexey Kodanev <alexey.kodanev@oracle.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/ipv6/ip6_vti.c | 20 ++++++++++++++++++++
    1 file changed, 20 insertions(+)

    --- a/net/ipv6/ip6_vti.c
    +++ b/net/ipv6/ip6_vti.c
    @@ -625,6 +625,7 @@ static void vti6_link_config(struct ip6_
    {
    struct net_device *dev = t->dev;
    struct __ip6_tnl_parm *p = &t->parms;
    + struct net_device *tdev = NULL;

    memcpy(dev->dev_addr, &p->laddr, sizeof(struct in6_addr));
    memcpy(dev->broadcast, &p->raddr, sizeof(struct in6_addr));
    @@ -637,6 +638,25 @@ static void vti6_link_config(struct ip6_
    dev->flags |= IFF_POINTOPOINT;
    else
    dev->flags &= ~IFF_POINTOPOINT;
    +
    + if (p->flags & IP6_TNL_F_CAP_XMIT) {
    + int strict = (ipv6_addr_type(&p->raddr) &
    + (IPV6_ADDR_MULTICAST | IPV6_ADDR_LINKLOCAL));
    + struct rt6_info *rt = rt6_lookup(t->net,
    + &p->raddr, &p->laddr,
    + p->link, strict);
    +
    + if (rt)
    + tdev = rt->dst.dev;
    + ip6_rt_put(rt);
    + }
    +
    + if (!tdev && p->link)
    + tdev = __dev_get_by_index(t->net, p->link);
    +
    + if (tdev)
    + dev->mtu = max_t(int, tdev->mtu - dev->hard_header_len,
    + IPV6_MIN_MTU);
    }

    /**

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