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

Jason Wang
2013-12-10T05:39:55Z

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@gmail.com>
>>> Cc: Vlad Yasevich <vyasevich@gmail.com>
>>> Cc: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
>>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>> 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@redhat.com>
>>
>> ---
>>
>> 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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