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    Subject[PATCH 5.4 349/408] ip_gre: set dev->hard_header_len and dev->needed_headroom properly
    Date
    From: Cong Wang <xiyou.wangcong@gmail.com>

    [ Upstream commit fdafed459998e2be0e877e6189b24cb7a0183224 ]

    GRE tunnel has its own header_ops, ipgre_header_ops, and sets it
    conditionally. When it is set, it assumes the outer IP header is
    already created before ipgre_xmit().

    This is not true when we send packets through a raw packet socket,
    where L2 headers are supposed to be constructed by user. Packet
    socket calls dev_validate_header() to validate the header. But
    GRE tunnel does not set dev->hard_header_len, so that check can
    be simply bypassed, therefore uninit memory could be passed down
    to ipgre_xmit(). Similar for dev->needed_headroom.

    dev->hard_header_len is supposed to be the length of the header
    created by dev->header_ops->create(), so it should be used whenever
    header_ops is set, and dev->needed_headroom should be used when it
    is not set.

    Reported-and-tested-by: syzbot+4a2c52677a8a1aa283cb@syzkaller.appspotmail.com
    Cc: William Tu <u9012063@gmail.com>
    Acked-by: Willem de Bruijn <willemb@google.com>
    Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
    Acked-by: Xie He <xie.he.0141@gmail.com>
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    net/ipv4/ip_gre.c | 15 +++++++++++----
    1 file changed, 11 insertions(+), 4 deletions(-)

    diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
    index 85ba1453ba5ca..fedad3a3e61b8 100644
    --- a/net/ipv4/ip_gre.c
    +++ b/net/ipv4/ip_gre.c
    @@ -603,9 +603,7 @@ static netdev_tx_t ipgre_xmit(struct sk_buff *skb,
    }

    if (dev->header_ops) {
    - /* Need space for new headers */
    - if (skb_cow_head(skb, dev->needed_headroom -
    - (tunnel->hlen + sizeof(struct iphdr))))
    + if (skb_cow_head(skb, 0))
    goto free_skb;

    tnl_params = (const struct iphdr *)skb->data;
    @@ -723,7 +721,11 @@ static void ipgre_link_update(struct net_device *dev, bool set_mtu)
    len = tunnel->tun_hlen - len;
    tunnel->hlen = tunnel->hlen + len;

    - dev->needed_headroom = dev->needed_headroom + len;
    + if (dev->header_ops)
    + dev->hard_header_len += len;
    + else
    + dev->needed_headroom += len;
    +
    if (set_mtu)
    dev->mtu = max_t(int, dev->mtu - len, 68);

    @@ -926,6 +928,7 @@ static void __gre_tunnel_init(struct net_device *dev)
    tunnel->parms.iph.protocol = IPPROTO_GRE;

    tunnel->hlen = tunnel->tun_hlen + tunnel->encap_hlen;
    + dev->needed_headroom = tunnel->hlen + sizeof(tunnel->parms.iph);

    dev->features |= GRE_FEATURES;
    dev->hw_features |= GRE_FEATURES;
    @@ -969,10 +972,14 @@ static int ipgre_tunnel_init(struct net_device *dev)
    return -EINVAL;
    dev->flags = IFF_BROADCAST;
    dev->header_ops = &ipgre_header_ops;
    + dev->hard_header_len = tunnel->hlen + sizeof(*iph);
    + dev->needed_headroom = 0;
    }
    #endif
    } else if (!tunnel->collect_md) {
    dev->header_ops = &ipgre_header_ops;
    + dev->hard_header_len = tunnel->hlen + sizeof(*iph);
    + dev->needed_headroom = 0;
    }

    return ip_tunnel_init(dev);
    --
    2.25.1


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