Re: [PATCH] nfc: nci: Fix uninit-value in nci_rx_work()

[Krzysztof Kozlowski <krzk@kernel.org>]

On 04/08/2024 12:57, Simon Horman wrote:
> On Sat, Aug 03, 2024 at 08:18:17PM +0800, zhanghao wrote:
>> Commit e624e6c3e777 ("nfc: Add a virtual nci device driver")
>> calls alloc_skb() with GFP_KERNEL as the argument flags.The
>> allocated heap memory was not initialized.This causes KMSAN
>> to detect an uninitialized value.
>>
>> Reported-by: syzbot+3da70a0abd7f5765b6ea@syzkaller.appspotmail.com
>> Closes: https://syzkaller.appspot.com/bug?extid=3da70a0abd7f5765b6ea
> 
> Hi,
> 
> I wonder if the problem reported above is caused by accessing packet
> data which is past the end of what is copied in virtual_ncidev_write().
> I.e. count is unusually short and this is not being detected.
> 
>> Fixes: e624e6c3e777 ("nfc: Add a virtual nci device driver")
>> Link: https://lore.kernel.org/all/000000000000747dd6061a974686@google.com/T/
>> Signed-off-by: zhanghao <zhanghao1@kylinos.cn>
>> ---
>>  drivers/nfc/virtual_ncidev.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/nfc/virtual_ncidev.c b/drivers/nfc/virtual_ncidev.c
>> index 6b89d596ba9a..ae1592db131e 100644
>> --- a/drivers/nfc/virtual_ncidev.c
>> +++ b/drivers/nfc/virtual_ncidev.c
>> @@ -117,7 +117,7 @@ static ssize_t virtual_ncidev_write(struct file *file,
>>  	struct virtual_nci_dev *vdev = file->private_data;
>>  	struct sk_buff *skb;
>>  
>> -	skb = alloc_skb(count, GFP_KERNEL);
>> +	skb = alloc_skb(count, GFP_KERNEL|__GFP_ZERO);
>>  	if (!skb)
>>  		return -ENOMEM;
> 
> I'm not sure this helps wrt initialising the memory as immediately below there
> is;
> 
> 	if (copy_from_user(skb_put(skb, count), buf, count)) {
> 		...
> 
> Which I assume will initialise count bytes of skb data.

Yeah, this looks like hiding the real issue.

Best regards,
Krzysztof