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

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Date:   Wed, 27 Sep 2017 14:58:07 +0200
From:   Alexander Potapenko <glider@...gle.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Dmitriy Vyukov <dvyukov@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>,
        Networking <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] tun: bail out from tun_get_user() if the skb is empty

On Wed, Sep 27, 2017 at 2:45 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> 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.
By the way I'm wondering if this is the only place where skb->data is
being accessed.
Isn't eth_type_trans() under IFF_TAP also touching it? Then we need to
check the size earlier.
>> 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 ;)
>
>
>



-- 
Alexander Potapenko
Software Engineer

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