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

Vlad Yasevich
2013-12-09T15:31:17Z

On 12/09/2013 05:55 AM, 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?
>
>> ---
>> 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?
>
>> 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.
>
>> }
>>
>> - 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;
>
> done:
> tun->dev->stats.tx_packets++;
>

You have to use 'offset' instead of 'total' when doing skb_copy and
adjust offset as you write the vlan header.

I think something like this will fix it:

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 782e38b..d71c393 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 {
@@ -1262,24 +1264,24 @@ static ssize_t tun_put_user(struct tun_struct *tun,

vlan_offset = offsetof(struct vlan_ethhdr, h_vlan_proto);
len = min_t(int, skb->len + VLAN_HLEN, len);
+ total += VLAN_HLEN;

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, offset, copy);
len -= copy;
- total += copy;
+ offset += 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, offset, copy);
len -= copy;
- total += copy;
+ offset += copy;
if (ret || !len)
goto done;
}

- skb_copy_datagram_const_iovec(skb, vlan_offset, iv, total, len);
- total += len;
+ skb_copy_datagram_const_iovec(skb, vlan_offset, iv, offset, len);

done:
tun->dev->stats.tx_packets++;

-vlad