netdev - Re: [PATCH v2] tun: bail out from tun_get

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Date:   Wed, 27 Sep 2017 05:45:44 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Alexander Potapenko <glider@...gle.com>
Cc:     davem@...emloft.net, edumazet@...gle.com, dvyukov@...gle.com,
        syzkaller@...glegroups.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] tun: bail out from tun_get_user() if the skb is empty

On Wed, 2017-09-27 at 05:42 -0700, Eric Dumazet wrote:

> Or something cleaner to avoid copy/paste and focus on proper
> skb->data[0] access and meaning.
> 
> Thanks.
> 
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 3c9985f299503ea65dad7eb3b47e2ab3bef87800..8ddb840687c1bdb24e4182612abc9e362624c3e9 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1496,11 +1496,13 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
>  	switch (tun->flags & TUN_TYPE_MASK) {
>  	case IFF_TUN:
>  		if (tun->flags & IFF_NO_PI) {
> -			switch (skb->data[0] & 0xf0) {
> -			case 0x40:
> +			u8 ip_proto = skb->len ? (skb->data[0] >> 4) : 0;

And name this variable ip_version ;)