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

On 2/21/21 1:39 PM, Sabyrzhan Tasbolatov wrote:

quoted

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.

quoted

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.

A protocol requiring contiguous physical memory allocations of up to KMALLOC_MAX_SIZE
bytes would be really unreliable.

I suggest we simply limit the allocations to 64KB, unless qrtr maintainers shout,
or start implementing scatter gather.