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    Subject[PATCH 5.4 113/142] xfrm: do pskb_pull properly in __xfrm_transport_prep
    Date
    From: Xin Long <lucien.xin@gmail.com>

    commit 06a0afcfe2f551ff755849ea2549b0d8409fd9a0 upstream.

    For transport mode, when ipv6 nexthdr is set, the packet format might
    be like:

    ----------------------------------------------------
    | | dest | | | | ESP | ESP |
    | IP6 hdr| opts.| ESP | TCP | Data | Trailer | ICV |
    ----------------------------------------------------

    and in __xfrm_transport_prep():

    pskb_pull(skb, skb->mac_len + sizeof(ip6hdr) + x->props.header_len);

    it will pull the data pointer to the wrong position, as it missed the
    nexthdrs/dest opts.

    This patch is to fix it by using:

    pskb_pull(skb, skb_transport_offset(skb) + x->props.header_len);

    as we can be sure transport_header points to ESP header at that moment.

    It also fixes a panic when packets with ipv6 nexthdr are sent over
    esp6 transport mode:

    [ 100.473845] kernel BUG at net/core/skbuff.c:4325!
    [ 100.478517] RIP: 0010:__skb_to_sgvec+0x252/0x260
    [ 100.494355] Call Trace:
    [ 100.494829] skb_to_sgvec+0x11/0x40
    [ 100.495492] esp6_output_tail+0x12e/0x550 [esp6]
    [ 100.496358] esp6_xmit+0x1d5/0x260 [esp6_offload]
    [ 100.498029] validate_xmit_xfrm+0x22f/0x2e0
    [ 100.499604] __dev_queue_xmit+0x589/0x910
    [ 100.502928] ip6_finish_output2+0x2a5/0x5a0
    [ 100.503718] ip6_output+0x6c/0x120
    [ 100.505198] xfrm_output_resume+0x4bf/0x530
    [ 100.508683] xfrm6_output+0x3a/0xc0
    [ 100.513446] inet6_csk_xmit+0xa1/0xf0
    [ 100.517335] tcp_sendmsg+0x27/0x40
    [ 100.517977] sock_sendmsg+0x3e/0x60
    [ 100.518648] __sys_sendto+0xee/0x160

    Fixes: c35fe4106b92 ("xfrm: Add mode handlers for IPsec on layer 2")
    Signed-off-by: Xin Long <lucien.xin@gmail.com>
    Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    net/xfrm/xfrm_device.c | 8 +++-----
    1 file changed, 3 insertions(+), 5 deletions(-)

    --- a/net/xfrm/xfrm_device.c
    +++ b/net/xfrm/xfrm_device.c
    @@ -25,12 +25,10 @@ static void __xfrm_transport_prep(struct
    struct xfrm_offload *xo = xfrm_offload(skb);

    skb_reset_mac_len(skb);
    - pskb_pull(skb, skb->mac_len + hsize + x->props.header_len);
    -
    - if (xo->flags & XFRM_GSO_SEGMENT) {
    - skb_reset_transport_header(skb);
    + if (xo->flags & XFRM_GSO_SEGMENT)
    skb->transport_header -= x->props.header_len;
    - }
    +
    + pskb_pull(skb, skb_transport_offset(skb) + x->props.header_len);
    }

    static void __xfrm_mode_tunnel_prep(struct xfrm_state *x, struct sk_buff *skb,

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