Commit c8c958a5 authored Nov 04, 2020 by Anant Thazhemadam Committed by Marc Kleine-Budde Nov 15, 2020

can: af_can: prevent potential access of uninitialized member in can_rcv()

In can_rcv(), cfd->len is uninitialized when skb->len = 0, and this
uninitialized cfd->len is accessed nonetheless by pr_warn_once().

Fix this uninitialized variable access by checking cfd->len's validity
condition (cfd->len > CAN_MAX_DLEN) separately after the skb->len's
condition is checked, and appropriately modify the log messages that
are generated as well.
In case either of the required conditions fail, the skb is freed and
NET_RX_DROP is returned, same as before.

Fixes: 8cb68751 ("can: af_can: can_rcv(): replace WARN_ONCE by pr_warn_once")
Reported-by: <syzbot+9bcb0c9409066696d3aa@syzkaller.appspotmail.com>
Tested-by: Anant Thazhemadam <anant.thazhemadam@gmail.com>
Signed-off-by: Anant Thazhemadam <anant.thazhemadam@gmail.com>
Link: https://lore.kernel.org/r/20201103213906.24219-2-anant.thazhemadam@gmail.com

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

parent ceb736e1

net/can/af_can.c

+14 −5

Original line number	Diff line number	Diff line
		@@ -677,16 +677,25 @@ static int can_rcv(struct sk_buff skb, struct net_device dev,
		{
		struct canfd_frame cfd = (struct canfd_frame )skb->data;

		if (unlikely(dev->type != ARPHRD_CAN \|\| skb->len != CAN_MTU \|\|
		cfd->len > CAN_MAX_DLEN)) {
		pr_warn_once("PF_CAN: dropped non conform CAN skbuf: dev type %d, len %d, datalen %d\n",
		if (unlikely(dev->type != ARPHRD_CAN \|\| skb->len != CAN_MTU)) {
		pr_warn_once("PF_CAN: dropped non conform CAN skbuff: dev type %d, len %d\n",
		dev->type, skb->len);
		goto free_skb;
		}

		/* This check is made separately since cfd->len would be uninitialized if skb->len = 0. */
		if (unlikely(cfd->len > CAN_MAX_DLEN)) {
		pr_warn_once("PF_CAN: dropped non conform CAN skbuff: dev type %d, len %d, datalen %d\n",
		dev->type, skb->len, cfd->len);
		kfree_skb(skb);
		return NET_RX_DROP;
		goto free_skb;
		}

		can_receive(skb, dev);
		return NET_RX_SUCCESS;

		free_skb:
		kfree_skb(skb);
		return NET_RX_DROP;
		}

		static int canfd_rcv(struct sk_buff skb, struct net_device dev,