Subject: Re: [Linux-kernel-mentees] [PATCH net] qrtr: Fix ZERO_SIZE_PTR deref in qrtr_tun_write_iter()

From: Eric Biggers <[email-masked]>
Date: Sun, 12 Jul 2020 14:36:31 -0700

On Sun, Jul 12, 2020 at 05:03:00PM -0400, Peilin Ye wrote:
> qrtr_tun_write_iter() is dereferencing `ZERO_SIZE_PTR`s when `from->count`
> equals to zero. Fix it by rejecting zero-length kzalloc() requests.
> 
> This patch fixes the following syzbot bug:
> 
>     https://syzkaller.appspot.com/bug?id=f56bbe6668873ee245986bbd23312b895fa5a50a
> 
> Reported-by: [email-masked]
> Signed-off-by: Peilin Ye <[email-masked]>
> ---
>  net/qrtr/tun.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/net/qrtr/tun.c b/net/qrtr/tun.c
> index 15ce9b642b25..5465e94ba8e5 100644
> --- a/net/qrtr/tun.c
> +++ b/net/qrtr/tun.c
> @@ -80,6 +80,9 @@ static ssize_t qrtr_tun_write_iter(struct kiocb *iocb, struct iov_iter *from)
>  	ssize_t ret;
>  	void *kbuf;
>  
> +	if (!len)
> +		return -EINVAL;
> +
>  	kbuf = kzalloc(len, GFP_KERNEL);
>  	if (!kbuf)
>  		return -ENOMEM;

Wasn't this already fixed by:

    commit 8ff41cc21714704ef0158a546c3c4d07fae2c952
    Author: Dan Carpenter <[email-masked]>
    Date:   Tue Jun 30 14:46:15 2020 +0300

        net: qrtr: Fix an out of bounds read qrtr_endpoint_post()