Re: [PATCH] udp: Prevent reuseport_select_sock from reading uninitialized socks

From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
To: Baptiste Lepers <baptiste.lepers@gmail.com>
Cc: David Miller <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Network Development <netdev@vger.kernel.org>
Subject: Re: [PATCH] udp: Prevent reuseport_select_sock from reading uninitialized socks
Date: Thu, 7 Jan 2021 00:27:07 -0500	[thread overview]
Message-ID: <CA+FuTScp=7nrd5vmAwoAdL-moX37Kx38a-QjqoWh-k1xxyJwMg@mail.gmail.com> (raw)
In-Reply-To: <20210107051110.12247-1-baptiste.lepers@gmail.com>

On Thu, Jan 7, 2021 at 12:11 AM Baptiste Lepers
<baptiste.lepers@gmail.com> wrote:
>
> reuse->socks[] is modified concurrently by reuseport_add_sock. To
> prevent reading values that have not been fully initialized, only read
> the array up until the last known safe index instead of incorrectly
> re-reading the last index of the array.
>
> Fixes: acdcecc61285f ("udp: correct reuseport selection with connected
> sockets")
> Signed-off-by: Baptiste Lepers <baptiste.lepers@gmail.com>

Acked-by: Willem de Bruijn <willemb@google.com>

Thanks. This also matches local variable socks as used to calculate i
and j with reciprocal_scale immediately above.

Please mark fixes [PATCH net] in the future.

> ---
>  net/core/sock_reuseport.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/core/sock_reuseport.c b/net/core/sock_reuseport.c
> index bbdd3c7b6cb5..b065f0a103ed 100644
> --- a/net/core/sock_reuseport.c
> +++ b/net/core/sock_reuseport.c
> @@ -293,7 +293,7 @@ struct sock *reuseport_select_sock(struct sock *sk,
>                         i = j = reciprocal_scale(hash, socks);
>                         while (reuse->socks[i]->sk_state == TCP_ESTABLISHED) {
>                                 i++;
> -                               if (i >= reuse->num_socks)
> +                               if (i >= socks)
>                                         i = 0;
>                                 if (i == j)
>                                         goto out;
> --
> 2.17.1
>