Re: [PATCH] net/qrtr: restrict user-controlled length in qrtr_tun_write_iter()

[Jakub Kicinski <kuba@kernel.org>]

On Tue,  2 Feb 2021 15:20:59 +0600 Sabyrzhan Tasbolatov wrote:
> syzbot found WARNING in qrtr_tun_write_iter [1] when write_iter length
> exceeds KMALLOC_MAX_SIZE causing order >= MAX_ORDER condition.
> 
> Additionally, there is no check for 0 length write.
> 
> [1]
> WARNING: mm/page_alloc.c:5011
> [..]
> Call Trace:
>  alloc_pages_current+0x18c/0x2a0 mm/mempolicy.c:2267
>  alloc_pages include/linux/gfp.h:547 [inline]
>  kmalloc_order+0x2e/0xb0 mm/slab_common.c:837
>  kmalloc_order_trace+0x14/0x120 mm/slab_common.c:853
>  kmalloc include/linux/slab.h:557 [inline]
>  kzalloc include/linux/slab.h:682 [inline]
>  qrtr_tun_write_iter+0x8a/0x180 net/qrtr/tun.c:83
>  call_write_iter include/linux/fs.h:1901 [inline]
> 
> Reported-by: syzbot+c2a7e5c5211605a90865@syzkaller.appspotmail.com
> Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
> ---
>  net/qrtr/tun.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/net/qrtr/tun.c b/net/qrtr/tun.c
> index 15ce9b642b25..b238c40a9984 100644
> --- a/net/qrtr/tun.c
> +++ b/net/qrtr/tun.c
> @@ -80,6 +80,12 @@ static ssize_t qrtr_tun_write_iter(struct kiocb *iocb, struct iov_iter *from)
>  	ssize_t ret;
>  	void *kbuf;
>  
> +	if (!len)
> +		return -EINVAL;
> +
> +	if (len > KMALLOC_MAX_SIZE)
> +		return -ENOMEM;
> +
>  	kbuf = kzalloc(len, GFP_KERNEL);

For potential, separate clean up - this is followed 
by copy_from_iter_full(len) kzalloc() can probably 
be replaced by kmalloc()?

>  	if (!kbuf)
>  		return -ENOMEM;