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    Subject[PATCH 5.9 243/255] net: udp: fix UDP header access on Fast/frag0 UDP GRO
    Date
    From: Alexander Lobakin <alobakin@pm.me>

    [ Upstream commit 4b1a86281cc1d0de46df3ad2cb8c1f86ac07681c ]

    UDP GRO uses udp_hdr(skb) in its .gro_receive() callback. While it's
    probably OK for non-frag0 paths (when all headers or even the entire
    frame are already in skb head), this inline points to junk when
    using Fast GRO (napi_gro_frags() or napi_gro_receive() with only
    Ethernet header in skb head and all the rest in the frags) and breaks
    GRO packet compilation and the packet flow itself.
    To support both modes, skb_gro_header_fast() + skb_gro_header_slow()
    are typically used. UDP even has an inline helper that makes use of
    them, udp_gro_udphdr(). Use that instead of troublemaking udp_hdr()
    to get rid of the out-of-order delivers.

    Present since the introduction of plain UDP GRO in 5.0-rc1.

    Fixes: e20cf8d3f1f7 ("udp: implement GRO for plain UDP sockets.")
    Cc: Eric Dumazet <edumazet@google.com>
    Signed-off-by: Alexander Lobakin <alobakin@pm.me>
    Acked-by: Willem de Bruijn <willemb@google.com>
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/ipv4/udp_offload.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/net/ipv4/udp_offload.c
    +++ b/net/ipv4/udp_offload.c
    @@ -366,7 +366,7 @@ out:
    static struct sk_buff *udp_gro_receive_segment(struct list_head *head,
    struct sk_buff *skb)
    {
    - struct udphdr *uh = udp_hdr(skb);
    + struct udphdr *uh = udp_gro_udphdr(skb);
    struct sk_buff *pp = NULL;
    struct udphdr *uh2;
    struct sk_buff *p;

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