Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Sabyrzhan Tasbolatov <snovitoll@gmail.com>
To:     eric.dumazet@gmail.com
Cc:     davem@davemloft.net, kuba@kernel.org, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org, snovitoll@gmail.com,
        syzbot+c2a7e5c5211605a90865@syzkaller.appspotmail.com
Subject: Re: [PATCH] net/qrtr: restrict length in qrtr_tun_write_iter()
Date:   Sun, 21 Feb 2021 18:39:12 +0600
Message-Id: <20210221123912.3185059-1-snovitoll@gmail.com>
In-Reply-To: <3b27dac1-45b9-15ad-c25e-2f5f3050907e@gmail.com>
References: <3b27dac1-45b9-15ad-c25e-2f5f3050907e@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

> Do we really expect to accept huge lengths here ?

Sorry for late response but I couldnt find any reference to the max
length of incoming data for qrtr TUN interface.

> qrtr_endpoint_post() will later attempt a netdev_alloc_skb() which will need
> some extra space (for struct skb_shared_info)

Thanks, you're right, qrtr_endpoint_post() will alloc another slab buffer.
We can check the length of skb allocation but we need to do following:

int qrtr_endpoint_post(.., const void *data, size_t len) 
{
	..
	when QRTR_PROTO_VER_1:
		hdrlen = sizeof(*data);
	when QRTR_PROTO_VER_2:
		hdrlen = sizeof(*data) + data->optlen;
	
	len = (KMALLOC_MAX_SIZE - hdrlen) % data->size;
	skb = netdev_alloc_skb(NULL, len);
	..
	skb_put_data(skb, data + hdrlen, size);


So it requires refactoring as in qrtr_tun_write_iter() we just allocate and
pass it to qrtr_endpoint_post() and there
we need to do len calculation as above *before* netdev_alloc_skb(NULL, len).

Perhaps there is a nicer solution though.