Subject: Re: tun issue after e0b46d0ee9c: tun: Use iovec iterators

From: Marcelo Ricardo Leitner <[email-masked]>
Date: Sat, 29 Nov 2014 03:08:09 -0200

On 28-11-2014 21:59, Herbert Xu wrote:
> On Fri, Nov 28, 2014 at 05:25:27PM -0200, Marcelo Ricardo Leitner wrote:
>>
>> I saw there are tun updates on Dave's queue but none seemed to handle this.
>>
>> I can't use current net-next
>> (799d2fff1858004526ad75d66a5dd8a5cce6ad40) on a kvm hypervisor
>> because tun got clogged somehow. Bisected down to:
>>
>> commit e0b46d0ee9c240c7430a47e9b0365674d4a04522
>> Author: Herbert Xu <[email-masked]>
>> Date:   Fri Nov 7 21:22:23 2014 +0800
>
> Does this patch help?

Yay, it does! Works for me, thanks Herbert.
I didn't test performance, but dhcp could get through.

Are you sure about the Fixes tag? Because bisect really pointed to e0b46d0ee9c.

Cheers,
Marcelo

> -- >8 --
> Subject: tun: Fix GSO meta-data handling in tun_get_user
>
> When we write the GSO meta-data in tun_get_user we end up advancing
> the IO vector twice, thus exhausting the user buffer before we can
> finish writing the packet.
>
> Fixes: f5ff53b4d97c ("{macvtap,tun}_get_user(): switch to iov_iter")
> Reported-by: Marcelo Ricardo Leitner <[email-masked]>
> Signed-off-by: Herbert Xu <[email-masked]>
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 4b743c6..9357871 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1052,7 +1052,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
>
>   		if (gso.hdr_len > len)
>   			return -EINVAL;
> -		iov_iter_advance(from, tun->vnet_hdr_sz);
> +		iov_iter_advance(iter, tun->vnet_hdr_sz - sizeof(gso));
>   	}
>
>   	if ((tun->flags & TUN_TYPE_MASK) == TUN_TAP_DEV) {
>
> Cheers,
>