Subject: Re: [PATCH] packet: fix leakage of tx_ring memory

From: Daniel Borkmann <[email-masked]>
Date: Fri, 01 Feb 2013 17:05:08 +0100

On 02/01/2013 02:57 PM, Phil Sutter wrote:
> When releasing a packet socket, the routine packet_set_ring() is reused
> to free rings instead of allocating them. But when calling it for the
> first time, it fills req->tp_block_nr with the value of rb->pg_vec_len
> which in the second invocation makes it bail out since req->tp_block_nr
> is greater zero but req->tp_block_size is zero.
>
> This patch solves the problem by passing a zeroed auto-variable to
> packet_set_ring() upon each invocation from packet_release().
>
> As far as I can tell, this issue exists even since 69e3c75 (net: TX_RING
> and packet mmap), i.e. the original inclusion of TX ring support into
> af_packet, but applies only to sockets with both RX and TX ring
> allocated, which is probably why this was unnoticed all the time.
>
> Signed-off-by: Phil Sutter <[email-masked]>
> Cc: Johann Baudy <[email-masked]>
> Cc: [email-masked]
> ---

[...]

> +static int packet_free_ring(struct sock *sk, int tx_ring)
> +{
> +	union tpacket_req_u req_u = { 0 };
> +
> +	return packet_set_ring(sk, &req_u, 1, tx_ring);
> +}
> +
>   /*
>    *	Close a PACKET socket. This is fairly simple. We immediately go
>    *	to 'closed' state and remove our protocol entry in the device list.
> @@ -2338,7 +2345,6 @@ static int packet_release(struct socket *sock)
>   	struct sock *sk = sock->sk;
>   	struct packet_sock *po;
>   	struct net *net;
> -	union tpacket_req_u req_u;
>
>   	if (!sk)
>   		return 0;
> @@ -2364,13 +2370,11 @@ static int packet_release(struct socket *sock)
>
>   	packet_flush_mclist(sk);
>
> -	memset(&req_u, 0, sizeof(req_u));
> -
>   	if (po->rx_ring.pg_vec)
> -		packet_set_ring(sk, &req_u, 1, 0);
> +		packet_free_ring(sk, 0);
>
>   	if (po->tx_ring.pg_vec)
> -		packet_set_ring(sk, &req_u, 1, 1);
> +		packet_free_ring(sk, 1);

Good catch!

Nitpicking:

I think it would be easier / more readable to simply move the memset into
the two ifs than introducing an extra function for just doing that.

(Also don't cc stable, since David is deciding about this anyway.)