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    Subject[PATCH 4.2.y-ckt 21/93] ipv4: l2tp: fix a potential issue in l2tp_ip_recv
    Date
    4.2.8-ckt9 -stable review patch.  If anyone has any objections, please let me know.

    ---8<------------------------------------------------------------

    From: Haishuang Yan <yanhaishuang@cmss.chinamobile.com>

    [ Upstream commit 5745b8232e942abd5e16e85fa9b27cc21324acf0 ]

    pskb_may_pull() can change skb->data, so we have to load ptr/optr at the
    right place.

    Signed-off-by: Haishuang Yan <yanhaishuang@cmss.chinamobile.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Kamal Mostafa <kamal@canonical.com>
    ---
    net/l2tp/l2tp_ip.c | 8 +++++---
    1 file changed, 5 insertions(+), 3 deletions(-)

    diff --git a/net/l2tp/l2tp_ip.c b/net/l2tp/l2tp_ip.c
    index 7964993..44ee068 100644
    --- a/net/l2tp/l2tp_ip.c
    +++ b/net/l2tp/l2tp_ip.c
    @@ -123,12 +123,11 @@ static int l2tp_ip_recv(struct sk_buff *skb)
    struct l2tp_tunnel *tunnel = NULL;
    int length;

    - /* Point to L2TP header */
    - optr = ptr = skb->data;
    -
    if (!pskb_may_pull(skb, 4))
    goto discard;

    + /* Point to L2TP header */
    + optr = ptr = skb->data;
    session_id = ntohl(*((__be32 *) ptr));
    ptr += 4;

    @@ -156,6 +155,9 @@ static int l2tp_ip_recv(struct sk_buff *skb)
    if (!pskb_may_pull(skb, length))
    goto discard;

    + /* Point to L2TP header */
    + optr = ptr = skb->data;
    + ptr += 4;
    pr_debug("%s: ip recv\n", tunnel->name);
    print_hex_dump_bytes("", DUMP_PREFIX_OFFSET, ptr, length);
    }
    --
    2.7.4
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