[PATCH net] net: dlink: fix null dereference in receive_packet()

[PATCH net] net: dlink: fix null dereference in receive_packet()

[Yeounsu Moon]

If `np->rx_skbuff[entry]` was not allocated before
reuse, `receive_packet()` will cause null dereference.

This patch fixes the issue by breaking out of the loop when
`np->rx_skbuff[entry]` is `NULL`.

Found by inspection.

Signed-off-by: Yeounsu Moon <yyyynoom@gmail.com>
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Tested-on: D-Link DGE-550T Rev-A3
---
 drivers/net/ethernet/dlink/dl2k.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/ethernet/dlink/dl2k.c b/drivers/net/ethernet/dlink/dl2k.c
index 1996d2e4e3e2..aa3840454fcb 100644
--- a/drivers/net/ethernet/dlink/dl2k.c
+++ b/drivers/net/ethernet/dlink/dl2k.c
@@ -969,6 +969,8 @@ receive_packet (struct net_device *dev)
 			if (pkt_len <= copy_thresh)
 				skb = netdev_alloc_skb_ip_align(dev, pkt_len);
 			if (!skb) {
+				if (!np->rx_skbuff[entry])
+					break;
 				dma_unmap_single(&np->pdev->dev,
 						 desc_to_dma(desc),
 						 np->rx_buf_sz,
-- 
2.51.0

Re: [PATCH net] net: dlink: fix null dereference in receive_packet()

[Simon Horman]

On Fri, Oct 10, 2025 at 04:02:22AM +0900, Yeounsu Moon wrote:
> If `np->rx_skbuff[entry]` was not allocated before
> reuse, `receive_packet()` will cause null dereference.
> 
> This patch fixes the issue by breaking out of the loop when
> `np->rx_skbuff[entry]` is `NULL`.

I see that if np->rx_skbuff[entry] there will be a dereference.
But I'm less clear on how this situation can occur.
So I think it would be worth adding some explanation of that
to the commit message.

Also, I do see that break will result in np->rx_skbuff[entry],
and other empty entries in that array, being refilled.
This is due to the refill loop that towards the end of receive_packet().
But perhaps it is worth mentioning that in the commit message too?

> 
> Found by inspection.

Thanks, that is clear.

> 
> Signed-off-by: Yeounsu Moon <yyyynoom@gmail.com>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Tested-on: D-Link DGE-550T Rev-A3

...

Re: [PATCH net] net: dlink: fix null dereference in receive_packet()

[Yeounsu Moon]

On Fri Oct 10, 2025 at 4:18 PM KST, Simon Horman wrote:
> On Fri, Oct 10, 2025 at 04:02:22AM +0900, Yeounsu Moon wrote:
>> If `np->rx_skbuff[entry]` was not allocated before
>> reuse, `receive_packet()` will cause null dereference.
>> 
>> This patch fixes the issue by breaking out of the loop when
>> `np->rx_skbuff[entry]` is `NULL`.
>
> I see that if np->rx_skbuff[entry] there will be a dereference.
> But I'm less clear on how this situation can occur.
When it failed to reallocate `skb`, and then a lot of packets come in at
that time, `skb_put()` in `receive_packet()` will cause a null dereference
and the kernel will panic.

> So I think it would be worth adding some explanation of that
> to the commit message.
Sorry, I'll make sure to describe the scenario more clearly in the commit
message next time.
>
> Also, I do see that break will result in np->rx_skbuff[entry],
> and other empty entries in that array, being refilled.
> This is due to the refill loop that towards the end of receive_packet().
Exactly, that is correct.
> But perhaps it is worth mentioning that in the commit message too?
You are right. I should mention the effect of the break in the commit
message as well. Sorry for making you point it out twice.