netdev - Re: [PATCH] net/qrtr: restrict length in qrtr_tun_write

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Date:   Sun, 21 Feb 2021 18:39:12 +0600
From:   Sabyrzhan Tasbolatov <snovitoll@...il.com>
To:     eric.dumazet@...il.com
Cc:     davem@...emloft.net, kuba@...nel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, snovitoll@...il.com,
        syzbot+c2a7e5c5211605a90865@...kaller.appspotmail.com
Subject: Re: [PATCH] net/qrtr: restrict length in qrtr_tun_write_iter()

> 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.