ACK: [bionic:linux, bionic:linux-hwe-5.0][PATCH] UBUNTU: SAUCE: net/packet: fix overflow in tpacket_rcv

[Thadeu Lima de Souza Cascardo]

On Fri, Sep 04, 2020 at 03:33:31PM -0300, Marcelo Henrique Cerri wrote:
> From: Or Cohen <orcohen at paloaltonetworks.com>
> 
> CVE-2020-14386
> 
> Using tp_reserve to calculate netoff can overflow as
> tp_reserve is unsigned int and netoff is unsigned short.
> 
> This may lead to macoff receving a smaller value then
> sizeof(struct virtio_net_hdr), and if po->has_vnet_hdr
> is set, an out-of-bounds write will occur when
> calling virtio_net_hdr_from_skb.
> 
> The bug is fixed by converting netoff to unsigned int
> and checking if it exceeds USHRT_MAX.
> 
> This addresses CVE-2020-14386
> 
> Fixes: 8913336a7e8d ("packet: add PACKET_RESERVE sockopt")
> Signed-off-by: Or Cohen <orcohen at paloaltonetworks.com>
> Signed-off-by: Eric Dumazet <edumazet at google.com>
> 
> [ snu: backported to 4.9, changed tp_drops counting/locking ]
> 
> Signed-off-by: Stefan Nuernberger <snu at amazon.com>
> CC: David Woodhouse <dwmw at amazon.co.uk>
> CC: Amit Shah <aams at amazon.com>
> CC: stable at vger.kernel.org
> 
> [ mhcerri: from the netdev mailing list:
>   https://lore.kernel.org/netdev/CAM6JnLf_8nwzq+UGO+amXpeApCDarJjwzOEHQd5qBhU7YKm3DQ@mail.gmail.com/
>   This is the fixed proposed on the mailing list for 4.9, this fix
>   should be intended to any kernel that doesn't have commit id 8e8e2951e309
>   ("net/packet: make tp_drops atomic"). For us, that means any kernel
>   before 5.3.
>   Tested with the reproducer proposed by the author.]
> Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri at canonical.com>

Acked-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>

> ---
>  net/packet/af_packet.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index 89d6b0957d07..cd5fbec69de8 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -2160,7 +2160,8 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
>  	int skb_len = skb->len;
>  	unsigned int snaplen, res;
>  	unsigned long status = TP_STATUS_USER;
> -	unsigned short macoff, netoff, hdrlen;
> +	unsigned short macoff, hdrlen;
> +	unsigned int netoff;
>  	struct sk_buff *copy_skb = NULL;
>  	struct timespec ts;
>  	__u32 ts_status;
> @@ -2223,6 +2224,12 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
>  		}
>  		macoff = netoff - maclen;
>  	}
> +	if (netoff > USHRT_MAX) {
> +		spin_lock(&sk->sk_receive_queue.lock);
> +		po->stats.stats1.tp_drops++;
> +		spin_unlock(&sk->sk_receive_queue.lock);
> +		goto drop_n_restore;
> +	}
>  	if (po->tp_version <= TPACKET_V2) {
>  		if (macoff + snaplen > po->rx_ring.frame_size) {
>  			if (po->copy_thresh &&
> -- 
> 2.25.1
> 
> 
> -- 
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