can: etas_es58x: populate ndo_change_mtu() to prevent buffer overflow

Summary

In the Linux kernel, the following vulnerability has been resolved: can: etas_es58x: populate ndo_change_mtu() to prevent buffer overflow Sending an PF_PACKET allows to bypass the CAN framework logic and to directly reach the xmit() function of a CAN driver. The only check which is performed by the PF_PACKET framework is to make sure that skb->len fits the interface's MTU. Unfortunately, because the etas_es58x driver does not populate its net_device_ops->ndo_change_mtu(), it is possible for an attacker to configure an invalid MTU by doing, for example: $ ip link set can0 mtu 9999 After doing so, the attacker could open a PF_PACKET socket using the ETH_P_CANXL protocol: socket(PF_PACKET, SOCK_RAW, htons(ETH_P_CANXL)); to inject a malicious CAN XL frames. For example: struct canxl_frame frame = { .flags = 0xff, .len = 2048, }; The CAN drivers' xmit() function are calling can_dev_dropped_skb() to check that the skb is valid, unfortunately under above conditions, the malicious packet is able to go through can_dev_dropped_skb() checks: 1. the skb->protocol is set to ETH_P_CANXL which is valid (the function does not check the actual device capabilities). 2. the length is a valid CAN XL length. And so, es58x_start_xmit() receives a CAN XL frame which it is not able to correctly handle and will thus misinterpret it as a CAN(FD) frame. This can result in a buffer overflow. For example, using the es581.4 variant, the frame will be dispatched to es581_4_tx_can_msg(), go through the last check at the beginning of this function: if (can_is_canfd_skb(skb)) return -EMSGSIZE; and reach this line: memcpy(tx_can_msg->data, cf->data, cf->len); Here, cf->len corresponds to the flags field of the CAN XL frame. In our previous example, we set canxl_frame->flags to 0xff. Because the maximum expected length is 8, a buffer overflow of 247 bytes occurs! Populate net_device_ops->ndo_change_mtu() to ensure that the interface's MTU can not be set to anything bigger than CAN_MTU or CANFD_MTU (depending on the device capabilities). By fixing the root cause, this prevents the buffer overflow.