netdev - Re: [PATCH net v2] atm: Fix Use-After-Free in do_vcc

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Date: Sat, 9 Dec 2023 10:07:56 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Hyunwoo Kim <v4bel@...ori.io>
Cc: davem@...emloft.net, kuba@...nel.org, imv4bel@...il.com, pabeni@...hat.com, 
	netdev@...r.kernel.org
Subject: Re: [PATCH net v2] atm: Fix Use-After-Free in do_vcc_ioctl

On Sat, Dec 9, 2023 at 10:05 AM Hyunwoo Kim <v4bel@...ori.io> wrote:
>
> Because do_vcc_ioctl() accesses sk->sk_receive_queue
> without holding a sk->sk_receive_queue.lock, it can
> cause a race with vcc_recvmsg().
> A use-after-free for skb occurs with the following flow.
> ```
> do_vcc_ioctl() -> skb_peek()
> vcc_recvmsg() -> skb_recv_datagram() -> skb_free_datagram()
> ```
> Add sk->sk_receive_queue.lock to do_vcc_ioctl() to fix this issue.
>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Hyunwoo Kim <v4bel@...ori.io>
> ---
> v1 -> v2: Change the code style
> ---
>  net/atm/ioctl.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/net/atm/ioctl.c b/net/atm/ioctl.c
> index 838ebf0cabbf..b7684abcf458 100644
> --- a/net/atm/ioctl.c
> +++ b/net/atm/ioctl.c
> @@ -72,15 +72,18 @@ static int do_vcc_ioctl(struct socket *sock, unsigned int cmd,
>                 goto done;
>         case SIOCINQ:
>         {
> +               long amount;
>                 struct sk_buff *skb;

This should be "int amount;", and should be put after the " struct
sk_buff *skb;" line for  proper style.




>
>                 if (sock->state != SS_CONNECTED) {
>                         error = -EINVAL;
>                         goto done;
>                 }
> +               spin_lock_irq(&sk->sk_receive_queue.lock);
>                 skb = skb_peek(&sk->sk_receive_queue);
> -               error = put_user(skb ? skb->len : 0,
> -                                (int __user *)argp) ? -EFAULT : 0;
> +               amount = skb ? skb->len : 0;
> +               spin_unlock_irq(&sk->sk_receive_queue.lock);
> +               error = put_user(amount, (int __user *)argp) ? -EFAULT : 0;
>                 goto done;
>         }
>         case ATM_SETSC:
> --
> 2.25.1
>