Subject: Re: [Bugme-new] [Bug 9888] New: tun device without protocol info header fails under IPv6

From: Max Krasnyansky <[email-masked]>
Date: Thu, 07 Feb 2008 20:58:04 -0800

Andrew Morton wrote:
> On Mon,  4 Feb 2008 13:46:13 -0800 (PST)
> [email-masked] wrote:
>>
>> Open a tun device as type TUN, set the TUN_NO_PI flag, and try sending an IPv6
>> packet. The packet appears at the interface under tcpdumps, but propagates no
>> further. This is because the default protocol info used for tun devices where
>> the TUN_NO_PI flag is set assumes IPv4 as can be seen by the initialization at
>> the top of the tun_get_user function in drivers/net/tun.c file given by
>>
>>         struct tun_pi pi = { 0, __constant_htons(ETH_P_IP) };
>>
>> This can easily be fixed by adding a quick check at the top of tun_get_user.
>> Basically the code that used to read
>>
>>         if (!(tun->flags & TUN_NO_PI)) {
>>                 if ((len -= sizeof(pi)) > count)
>>                         return -EINVAL;
>>
>>                 if(memcpy_fromiovec((void *)&pi, iv, sizeof(pi)))
>>                         return -EFAULT;
>>         }
>>
>> when changed to read
>>
>>         if (!(tun->flags & TUN_NO_PI)) {
>>                 if ((len -= sizeof(pi)) > count)
>>                         return -EINVAL;
>>
>>                 if(memcpy_fromiovec((void *)&pi, iv, sizeof(pi)))
>>                         return -EFAULT;
>>         }
>>         else {
>>           /* Fixup default pi if IPv6 rather than IPv4 */
>>           if (((tun->flags & TUN_TYPE_MASK) == TUN_TUN_DEV) &&
>>               (*(char *)(iv->iov_base)      == 0x60)) {
>>             pi.proto = __constant_htons(ETH_P_IPV6);
>>           }
>>         }
>>
>> fixes the problem. 
>>
>> How do we get this in as part of the maintained codebase??
>>
> 
> Please email a tested patch prepared as described in
> 
> 	Documentation/SubmittingPatches
> 	Documentation/SubmitChecklist
> 	http://www.zip.com.au/~akpm/linux/patches/stuff/tpp.txt
> 
> to
> 
> 	Maxim Krasnyansky <[email-masked]>
> 	"David S. Miller" <[email-masked]>
> 	Andrew Morton <[email-masked]>
> 	[email-masked]

btw I'd be ok with this fix. But I guess the questions is why not use 
struct tun_pi in the apps instead ?

Max