ACK: [Trusty SRU][CVE-2016-8632][PATCH 1/1] tipc: check minimum bearer MTU

[Colin Ian King]

On 06/09/17 13:02, Kleber Sacilotto de Souza wrote:
> From: Michal Kubeček <mkubecek at suse.cz>
> 
> Qian Zhang (张谦) reported a potential socket buffer overflow in
> tipc_msg_build() which is also known as CVE-2016-8632: due to
> insufficient checks, a buffer overflow can occur if MTU is too short for
> even tipc headers. As anyone can set device MTU in a user/net namespace,
> this issue can be abused by a regular user.
> 
> As agreed in the discussion on Ben Hutchings' original patch, we should
> check the MTU at the moment a bearer is attached rather than for each
> processed packet. We also need to repeat the check when bearer MTU is
> adjusted to new device MTU. UDP case also needs a check to avoid
> overflow when calculating bearer MTU.
> 
> Fixes: b97bf3fd8f6a ("[TIPC] Initial merge")
> Signed-off-by: Michal Kubecek <mkubecek at suse.cz>
> Reported-by: Qian Zhang (张谦) <zhangqian-c at 360.cn>
> Acked-by: Ying Xue <ying.xue at windriver.com>
> Signed-off-by: David S. Miller <davem at davemloft.net>
> 
> CVE-2016-8632
> (backported from commit 3de81b758853f0b29c61e246679d20b513c4cfec)
> [kleber:
>  - Adjust context
>  - Duplicate macro definitions in bearer.h to avoid mutual inclusion
>  - Duplicate bearer changes for eth and ib media
>  - Drop changes in udp_media.c]
> Signed-off-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>
> ---
>  net/tipc/bearer.h    | 16 ++++++++++++++++
>  net/tipc/eth_media.c | 11 +++++++++--
>  net/tipc/ib_media.c  | 11 +++++++++--
>  3 files changed, 34 insertions(+), 4 deletions(-)
> 
> diff --git a/net/tipc/bearer.h b/net/tipc/bearer.h
> index e5e04be6fffa..cc8bc3b7cb6f 100644
> --- a/net/tipc/bearer.h
> +++ b/net/tipc/bearer.h
> @@ -58,6 +58,13 @@
>  #define TIPC_MEDIA_TYPE_ETH	1
>  #define TIPC_MEDIA_TYPE_IB	2
>  
> +/* Message header sizes from msg.h - duplicated to avoid mutual inclusion */
> +#define INT_H_SIZE                40
> +#define MAX_H_SIZE                60
> +
> +/* minimum bearer MTU */
> +#define TIPC_MIN_BEARER_MTU	(MAX_H_SIZE + INT_H_SIZE)
> +
>  /**
>   * struct tipc_media_addr - destination address used by TIPC bearers
>   * @value: address info (format defined by media)
> @@ -210,4 +217,13 @@ static inline void tipc_bearer_send(struct tipc_bearer *b, struct sk_buff *buf,
>  	b->media->send_msg(buf, b, dest);
>  }
>  
> +/* check if device MTU is too low for tipc headers */
> +static inline bool tipc_mtu_bad(struct net_device *dev, unsigned int reserve)
> +{
> +	if (dev->mtu >= TIPC_MIN_BEARER_MTU + reserve)
> +		return false;
> +	netdev_warn(dev, "MTU too low for tipc bearer\n");
> +	return true;
> +}
> +
>  #endif	/* _TIPC_BEARER_H */
> diff --git a/net/tipc/eth_media.c b/net/tipc/eth_media.c
> index f80d59f5a161..3fe074af15ec 100644
> --- a/net/tipc/eth_media.c
> +++ b/net/tipc/eth_media.c
> @@ -180,6 +180,10 @@ static int enable_media(struct tipc_bearer *tb_ptr)
>  	dev = dev_get_by_name(&init_net, driver_name);
>  	if (!dev)
>  		return -ENODEV;
> +	if (tipc_mtu_bad(dev, 0)) {
> +		dev_put(dev);
> +		return -EINVAL;
> +	}
>  
>  	/* Create Ethernet bearer for device */
>  	eb_ptr->dev = dev;
> @@ -258,8 +262,6 @@ static int recv_notification(struct notifier_block *nb, unsigned long evt,
>  	if (!eb_ptr->bearer)
>  		return NOTIFY_DONE;		/* bearer had been disabled */
>  
> -	eb_ptr->bearer->mtu = dev->mtu;
> -
>  	switch (evt) {
>  	case NETDEV_CHANGE:
>  		if (netif_carrier_ok(dev))
> @@ -274,6 +276,11 @@ static int recv_notification(struct notifier_block *nb, unsigned long evt,
>  		tipc_block_bearer(eb_ptr->bearer);
>  		break;
>  	case NETDEV_CHANGEMTU:
> +		if (tipc_mtu_bad(dev, 0)) {
> +			tipc_disable_bearer(eb_ptr->bearer->name);
> +			break;
> +		}
> +		eb_ptr->bearer->mtu = dev->mtu;
>  	case NETDEV_CHANGEADDR:
>  		tipc_block_bearer(eb_ptr->bearer);
>  		tipc_continue(eb_ptr->bearer);
> diff --git a/net/tipc/ib_media.c b/net/tipc/ib_media.c
> index c13989297464..c34380b9357c 100644
> --- a/net/tipc/ib_media.c
> +++ b/net/tipc/ib_media.c
> @@ -173,6 +173,10 @@ static int enable_media(struct tipc_bearer *tb_ptr)
>  	dev = dev_get_by_name(&init_net, driver_name);
>  	if (!dev)
>  		return -ENODEV;
> +	if (tipc_mtu_bad(dev, 0)) {
> +		dev_put(dev);
> +		return -EINVAL;
> +	}
>  
>  	/* Create InfiniBand bearer for device */
>  	ib_ptr->dev = dev;
> @@ -251,8 +255,6 @@ static int recv_notification(struct notifier_block *nb, unsigned long evt,
>  	if (!ib_ptr->bearer)
>  		return NOTIFY_DONE;		/* bearer had been disabled */
>  
> -	ib_ptr->bearer->mtu = dev->mtu;
> -
>  	switch (evt) {
>  	case NETDEV_CHANGE:
>  		if (netif_carrier_ok(dev))
> @@ -267,6 +269,11 @@ static int recv_notification(struct notifier_block *nb, unsigned long evt,
>  		tipc_block_bearer(ib_ptr->bearer);
>  		break;
>  	case NETDEV_CHANGEMTU:
> +		if (tipc_mtu_bad(dev, 0)) {
> +			tipc_disable_bearer(ib_ptr->bearer->name);
> +			break;
> +		}
> +		ib_ptr->bearer->mtu = dev->mtu;
>  	case NETDEV_CHANGEADDR:
>  		tipc_block_bearer(ib_ptr->bearer);
>  		tipc_continue(ib_ptr->bearer);
> 
Testing looks good to me.

Acked-by: Colin Ian King <colin.king at canonical.com>