Re: [PATCH net 1/2] tun: unbreak truncated packet signalling

[Jason Wang]

On 12/09/2013 06:56 PM, Michael S. Tsirkin wrote:
> On Mon, Dec 09, 2013 at 12:55:29PM +0200, Michael S. Tsirkin wrote:
>> On Mon, Dec 09, 2013 at 06:25:16PM +0800, Jason Wang wrote:
>>> Commit 6680ec68eff47d36f67b4351bc9836fd6cba9532
>>> (tuntap: hardware vlan tx support) breaks the truncated packet signal by never
>>> return a length greater than iov length in tun_put_user(). This patch fixes this
>>> by always return the length of packet plus possible vlan header. Caller can
>>> detect the truncated packet by comparing the return value and the size of iov
>>> length.
>>>
>>> Reported-by: Vlad Yasevich <vyasevich@xxxxxxxxx>
>>> Cc: Vlad Yasevich <vyasevich@xxxxxxxxx>
>>> Cc: Zhi Yong Wu <wuzhy@xxxxxxxxxxxxxxxxxx>
>>> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
>> So writer gets back a value greater than what was written?
> Pls ignore this question - wrote it before I understood the
> patch, and forgot to remove.
> The rest of the comments and the proposed alternative patch
> still stand.
>
>>> ---
>>> The patch is needed for stable.
>>> ---
>>>  drivers/net/tun.c | 23 ++++++++++++-----------
>>>  1 file changed, 12 insertions(+), 11 deletions(-)
>>>
>>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
>>> index e26cbea..dd1bd7a 100644
>>> --- a/drivers/net/tun.c
>>> +++ b/drivers/net/tun.c
>>> @@ -1183,7 +1183,11 @@ static ssize_t tun_put_user(struct tun_struct *tun,
>>>  			    const struct iovec *iv, int len)
>>>  {
>>>  	struct tun_pi pi = { 0, skb->protocol };
>>> -	ssize_t total = 0;
>>> +	struct {
>>> +		__be16 h_vlan_proto;
>>> +		__be16 h_vlan_TCI;
>>> +	} veth;
>>> +	ssize_t total = 0, off = 0;
>> Why off = 0 here?
>> We initialize it to total unconditionally, don't we?

True, it's useless.
>>>  	int vlan_offset = 0;
>>>  
>>>  	if (!(tun->flags & TUN_NO_PI)) {
>>> @@ -1248,14 +1252,11 @@ static ssize_t tun_put_user(struct tun_struct *tun,
>>>  		total += tun->vnet_hdr_sz;
>>>  	}
>>>  
>>> +	off = total;
>>>  	if (!vlan_tx_tag_present(skb)) {
>>>  		len = min_t(int, skb->len, len);
>>>  	} else {
>>>  		int copy, ret;
>>> -		struct {
>>> -			__be16 h_vlan_proto;
>>> -			__be16 h_vlan_TCI;
>>> -		} veth;
>>>  
>>>  		veth.h_vlan_proto = skb->vlan_proto;
>>>  		veth.h_vlan_TCI = htons(vlan_tx_tag_get(skb));
>>> @@ -1264,22 +1265,22 @@ static ssize_t tun_put_user(struct tun_struct *tun,
>>>  		len = min_t(int, skb->len + VLAN_HLEN, len);
>>>  
>>>  		copy = min_t(int, vlan_offset, len);
>>> -		ret = skb_copy_datagram_const_iovec(skb, 0, iv, total, copy);
>>> +		ret = skb_copy_datagram_const_iovec(skb, 0, iv, off, copy);
>>>  		len -= copy;
>>> -		total += copy;
>>> +		off += copy;
>>>  		if (ret || !len)
>>>  			goto done;
>>>  
>>>  		copy = min_t(int, sizeof(veth), len);
>>> -		ret = memcpy_toiovecend(iv, (void *)&veth, total, copy);
>>> +		ret = memcpy_toiovecend(iv, (void *)&veth, off, copy);
>>>  		len -= copy;
>>> -		total += copy;
>>> +		off += copy;
>>>  		if (ret || !len)
>>>  			goto done;
>> This seems wrong: if one of the branches above is taken, total is
>> never incremented.

Right.
>>>  	}
>>>  
>>> -	skb_copy_datagram_const_iovec(skb, vlan_offset, iv, total, len);
>>> -	total += len;
>>> +	skb_copy_datagram_const_iovec(skb, vlan_offset, iv, off, len);
>>> +	total += skb->len + (vlan_offset ? sizeof(veth) : 0);
>>>  
>>>  done:
>>>  	tun->dev->stats.tx_packets++;
>> I also think it's inelegant that the veth struct is now in the
>> outside scope, and the extra ? is also ugly.
>>
>> Here's a smaller patch to fix all these problems - what do you think?
>>
>>
>>
>> Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
>>
>> ---
>>
>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
>> index 782e38b..3297e41 100644
>> --- a/drivers/net/tun.c
>> +++ b/drivers/net/tun.c
>> @@ -1183,7 +1183,7 @@ static ssize_t tun_put_user(struct tun_struct *tun,
>>  			    const struct iovec *iv, int len)
>>  {
>>  	struct tun_pi pi = { 0, skb->protocol };
>> -	ssize_t total = 0;
>> +	ssize_t total = 0, offset;
>>  	int vlan_offset = 0;
>>  
>>  	if (!(tun->flags & TUN_NO_PI)) {
>> @@ -1248,6 +1248,8 @@ static ssize_t tun_put_user(struct tun_struct *tun,
>>  		total += tun->vnet_hdr_sz;
>>  	}
>>  
>> +	offset = total;
>> +	total += skb->len;
>>  	if (!vlan_tx_tag_present(skb)) {
>>  		len = min_t(int, skb->len, len);
>>  	} else {
>> @@ -1257,6 +1259,8 @@ static ssize_t tun_put_user(struct tun_struct *tun,
>>  			__be16 h_vlan_TCI;
>>  		} veth;
>>  
>> +		total += sizeof(veth);
>> +
>>  		veth.h_vlan_proto = skb->vlan_proto;
>>  		veth.h_vlan_TCI = htons(vlan_tx_tag_get(skb));
>>  
>> @@ -1279,7 +1283,6 @@ static ssize_t tun_put_user(struct tun_struct *tun,
>>  	}
>>  
>>  	skb_copy_datagram_const_iovec(skb, vlan_offset, iv, total, len);
>> -	total += len;
>>  

We should use offset here and it should be advanced during vlan tag putting.
>>  done:
>>  	tun->dev->stats.tx_packets++;
>>
>>> -- 
>>> 1.8.3.2
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