[PATCH 5.4 075/158] can: af_can: prevent potential access of uninitialized member in can_rcv()

Greg Kroah-Hartman
2020-11-23T12:37:11Z

From: Anant Thazhemadam <anant.thazhemadam@gmail.com>

[ Upstream commit c8c958a58fc67f353289986850a0edf553435702 ]

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: 8cb68751c115 ("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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/can/af_can.c | 19 ++++++++++++++-----
1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/net/can/af_can.c b/net/can/af_can.c
index 128d37a4c2e0b..09d2329719c17 100644
--- a/net/can/af_can.c
+++ b/net/can/af_can.c
@@ -675,16 +675,25 @@ 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,
--
2.27.0