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

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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: 8cb68751c1 ("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>
This commit is contained in:
Anant Thazhemadam 2020-11-04 03:09:05 +05:30 committed by Marc Kleine-Budde
parent ceb736e1d4
commit c8c958a58f
1 changed files with 14 additions and 5 deletions
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19
net/can/af_can.c
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@ -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,