Re: [PATCH net-next] tcp: cleanup sk_tx_skb_cache before reuse

[Soheil Hassas Yeganeh <soheil@google.com>]

On Fri, Mar 29, 2019 at 3:46 PM Eric Dumazet <edumazet@google.com> wrote:
>
> TCP stack relies on the fact that a freshly allocated skb
> has skb->cb[] and skb_shinfo(skb)->tx_flags cleared.
>
> When recycling tx skb, we must ensure these fields are cleared.
>
> Fixes: 472c2e07eef0 ("tcp: add one skb cache for tx")
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Soheil Hassas Yeganeh <soheil@google.com>
> Cc: Willem de Bruijn <willemb@google.com>

Acked-by: Soheil Hassas Yeganeh <soheil@google.com>

Nice catch! Thank you!

> ---
>  net/ipv4/tcp.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 82bd707c03472f2cebb1a90d5f1c13acc821468f..603e770d59b3db96adca9602319d2f6970a56285 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -872,6 +872,8 @@ struct sk_buff *sk_stream_alloc_skb(struct sock *sk, int size, gfp_t gfp,
>                         sk->sk_tx_skb_cache = NULL;
>                         pskb_trim(skb, 0);
>                         INIT_LIST_HEAD(&skb->tcp_tsorted_anchor);
> +                       skb_shinfo(skb)->tx_flags = 0;
> +                       memset(TCP_SKB_CB(skb), 0, sizeof(struct tcp_skb_cb));
>                         return skb;
>                 }
>         }
> --
> 2.21.0.392.gf8f6787159e-goog
>