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    Subject[PATCH 4.16 008/161] packet: in packet_snd start writing at link layer allocation
    Date
    4.16-stable review patch.  If anyone has any objections, please let me know.

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

    From: Willem de Bruijn <willemb@google.com>

    [ Upstream commit b84bbaf7a6c8cca24f8acf25a2c8e46913a947ba ]

    Packet sockets allow construction of packets shorter than
    dev->hard_header_len to accommodate protocols with variable length
    link layer headers. These packets are padded to dev->hard_header_len,
    because some device drivers interpret that as a minimum packet size.

    packet_snd reserves dev->hard_header_len bytes on allocation.
    SOCK_DGRAM sockets call skb_push in dev_hard_header() to ensure that
    link layer headers are stored in the reserved range. SOCK_RAW sockets
    do the same in tpacket_snd, but not in packet_snd.

    Syzbot was able to send a zero byte packet to a device with massive
    116B link layer header, causing padding to cross over into skb_shinfo.
    Fix this by writing from the start of the llheader reserved range also
    in the case of packet_snd/SOCK_RAW.

    Update skb_set_network_header to the new offset. This also corrects
    it for SOCK_DGRAM, where it incorrectly double counted reserve due to
    the skb_push in dev_hard_header.

    Fixes: 9ed988cd5915 ("packet: validate variable length ll headers")
    Reported-by: syzbot+71d74a5406d02057d559@syzkaller.appspotmail.com
    Signed-off-by: Willem de Bruijn <willemb@google.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/packet/af_packet.c | 4 +++-
    1 file changed, 3 insertions(+), 1 deletion(-)

    --- a/net/packet/af_packet.c
    +++ b/net/packet/af_packet.c
    @@ -2903,13 +2903,15 @@ static int packet_snd(struct socket *soc
    if (skb == NULL)
    goto out_unlock;

    - skb_set_network_header(skb, reserve);
    + skb_reset_network_header(skb);

    err = -EINVAL;
    if (sock->type == SOCK_DGRAM) {
    offset = dev_hard_header(skb, dev, ntohs(proto), addr, NULL, len);
    if (unlikely(offset < 0))
    goto out_free;
    + } else if (reserve) {
    + skb_push(skb, reserve);
    }

    /* Returns -EFAULT on error */

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