netdev - Re: [RFC PATCH 4/5] mlx4: add support for fast rx drop bpf program

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 01 Apr 2016 19:08:31 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Brenden Blanco <bblanco@...mgrid.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org, tom@...bertland.com,
	alexei.starovoitov@...il.com, gerlitz@...lanox.com,
	daniel@...earbox.net, john.fastabend@...il.com, brouer@...hat.com
Subject: Re: [RFC PATCH 4/5] mlx4: add support for fast rx drop bpf program

On Fri, 2016-04-01 at 18:21 -0700, Brenden Blanco wrote:
> Add support for the BPF_PROG_TYPE_PHYS_DEV hook in mlx4 driver.  Since
> bpf programs require a skb context to navigate the packet, build a
> percpu fake skb with the minimal fields. This avoids the costly
> allocation for packets that end up being dropped.
> 

> +		/* A bpf program gets first chance to drop the packet. It may
> +		 * read bytes but not past the end of the frag. A non-zero
> +		 * return indicates packet should be dropped.
> +		 */
> +		if (prog) {
> +			struct ethhdr *ethh;
> +
> +			ethh = (struct ethhdr *)(page_address(frags[0].page) +
> +						 frags[0].page_offset);
> +			if (mlx4_call_bpf(prog, ethh, length)) {
> +				priv->stats.rx_dropped++;
> +				goto next;
> +			}
> +		}
> +

1) mlx4 can use multiple fragments (priv->num_frags) to hold an Ethernet
frame. 

Still you pass a single fragment but total 'length' here : BPF program
can read past the end of this first fragment and panic the box.

Please take a look at mlx4_en_complete_rx_desc() and you'll see what I
mean.

2) priv->stats.rx_dropped is shared by all the RX queues -> false
sharing.

   This is probably the right time to add a rx_dropped field in struct
mlx4_en_rx_ring since you guys want to drop 14 Mpps, and 50 Mpps on
higher speed links.