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

[Simon Horman]

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@xxxxxxxxxxxxxxxxxxxxxxxxx
> 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@xxxxxxxxxx/T/
> Signed-off-by: zhanghao <zhanghao1@xxxxxxxxxx>
> ---
>  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.