netdev - Re: [PATCH net] skbuff: fix incorrect msg

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Date:   Wed, 9 Jun 2021 20:17:26 -0400
From:   Soheil Hassas Yeganeh <soheil@...gle.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     netdev <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Talal Ahmad <talalahmad@...gle.com>
Subject: Re: [PATCH net] skbuff: fix incorrect msg_zerocopy copy notifications

On Wed, Jun 9, 2021 at 6:42 PM Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
>
> From: Willem de Bruijn <willemb@...gle.com>
>
> msg_zerocopy signals if a send operation required copying with a flag
> in serr->ee.ee_code.
>
> This field can be incorrect as of the below commit, as a result of
> both structs uarg and serr pointing into the same skb->cb[].
>
> uarg->zerocopy must be read before skb->cb[] is reinitialized to hold
> serr. Similar to other fields len, hi and lo, use a local variable to
> temporarily hold the value.
>
> This was not a problem before, when the value was passed as a function
> argument.
>
> Fixes: 75518851a2a0 ("skbuff: Push status and refcounts into sock_zerocopy_callback")
> Reported-by: Talal Ahmad <talalahmad@...gle.com>
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>

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

Thank you for the fix!

> ---
>  net/core/skbuff.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 3ad22870298c..bbc3b4b62032 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -1253,6 +1253,7 @@ static void __msg_zerocopy_callback(struct ubuf_info *uarg)
>         struct sock *sk = skb->sk;
>         struct sk_buff_head *q;
>         unsigned long flags;
> +       bool is_zerocopy;
>         u32 lo, hi;
>         u16 len;
>
> @@ -1267,6 +1268,7 @@ static void __msg_zerocopy_callback(struct ubuf_info *uarg)
>         len = uarg->len;
>         lo = uarg->id;
>         hi = uarg->id + len - 1;
> +       is_zerocopy = uarg->zerocopy;
>
>         serr = SKB_EXT_ERR(skb);
>         memset(serr, 0, sizeof(*serr));
> @@ -1274,7 +1276,7 @@ static void __msg_zerocopy_callback(struct ubuf_info *uarg)
>         serr->ee.ee_origin = SO_EE_ORIGIN_ZEROCOPY;
>         serr->ee.ee_data = hi;
>         serr->ee.ee_info = lo;
> -       if (!uarg->zerocopy)
> +       if (!is_zerocopy)
>                 serr->ee.ee_code |= SO_EE_CODE_ZEROCOPY_COPIED;
>
>         q = &sk->sk_error_queue;
> --
> 2.32.0.rc1.229.g3e70b5a671-goog
>