[PATCH 0/2] prevent potential access of uninitialized members in can_rcv() and canfd_rcv()

[PATCH 0/2] prevent potential access of uninitialized members in can_rcv() and canfd_rcv()

[Anant Thazhemadam]

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

Performing the validation check for cfd->len separately, after the 
validation check for skb->len is done, resolves this issue in both 
instances, without compromising the degree of detail provided in the
log messages.

Anant Thazhemadam (2):
  can: af_can: prevent potential access of uninitialized member in
    can_rcv()
  can: af_can: prevent potential access of uninitialized member in
    canfd_rcv()

 net/can/af_can.c | 38 ++++++++++++++++++++++++++++----------
 1 file changed, 28 insertions(+), 10 deletions(-)

-- 
2.25.1

[PATCH 1/2] can: af_can: prevent potential access of uninitialized member in can_rcv()

[Anant Thazhemadam]

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>
---
 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 ea29a6d97ef5..8ea01524f062 100644
--- a/net/can/af_can.c
+++ b/net/can/af_can.c
@@ -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,
-- 
2.25.1

[PATCH 2/2] can: af_can: prevent potential access of uninitialized member in canfd_rcv()

[Anant Thazhemadam]

In canfd_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 > CANFD_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: d4689846881d ("can: af_can: canfd_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>
---
This patch was locally tested using the reproducer and .config file
generated by syzbot.

 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 8ea01524f062..d759334f8843 100644
--- a/net/can/af_can.c
+++ b/net/can/af_can.c
@@ -703,16 +703,25 @@ static int canfd_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 != CANFD_MTU ||
-		     cfd->len > CANFD_MAX_DLEN)) {
-		pr_warn_once("PF_CAN: dropped non conform CAN FD skbuf: dev type %d, len %d, datalen %d\n",
+	if (unlikely(dev->type != ARPHRD_CAN || skb->len != CANFD_MTU)) {
+		pr_warn_once("PF_CAN: dropped non conform CAN FD 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 > CANFD_MAX_DLEN)) {
+		pr_warn_once("PF_CAN: dropped non conform CAN FD 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;
 }
 
 /* af_can protocol functions */
-- 
2.25.1

Re: [PATCH 0/2] prevent potential access of uninitialized members in can_rcv() and canfd_rcv()

[Marc Kleine-Budde]

[-- Attachment #1.1: Type: text/plain, Size: 1066 bytes --]

On 11/3/20 10:39 PM, Anant Thazhemadam wrote:
> In both can_rcv(), and canfd_rcv(), when skb->len = 0, cfd->len 
> (which is uninitialized) is accessed by pr_warn_once().
> 
> Performing the validation check for cfd->len separately, after the 
> validation check for skb->len is done, resolves this issue in both 
> instances, without compromising the degree of detail provided in the
> log messages.
> 
> Anant Thazhemadam (2):
>   can: af_can: prevent potential access of uninitialized member in
>     can_rcv()
>   can: af_can: prevent potential access of uninitialized member in
>     canfd_rcv()
> 
>  net/can/af_can.c | 38 ++++++++++++++++++++++++++++----------
>  1 file changed, 28 insertions(+), 10 deletions(-)
> 

Applied both to linux-can/testing

Tnx,
Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
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