From: Eric Dumazet <eric.duma...@gmail.com>
Date: Tue, 18 Apr 2017 08:51:51 -0700
> On Tue, 2017-04-18 at 15:48 +0100, James Hughes wrote:
>> The driver was failing to check that the SKB wasn't cloned
>> before adding checksum data or adding header data.
>> Replace existing handling to extend the buffer with
>> skb_cow. Don't use skb_cow_head as the sw checksum
>> code modifies the data portion.
>>
>> Signed-off-by: James Hughes <james.hug...@raspberrypi.org>
>> ---
>> drivers/net/usb/smsc95xx.c | 10 +++-------
>> 1 file changed, 3 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/net/usb/smsc95xx.c b/drivers/net/usb/smsc95xx.c
>> index df60c98..04f6397 100644
>> --- a/drivers/net/usb/smsc95xx.c
>> +++ b/drivers/net/usb/smsc95xx.c
>> @@ -2067,13 +2067,9 @@ static struct sk_buff *smsc95xx_tx_fixup(struct
>> usbnet *dev,
>> /* We do not advertise SG, so skbs should be already linearized */
>> BUG_ON(skb_shinfo(skb)->nr_frags);
>>
>> - if (skb_headroom(skb) < overhead) {
>> - struct sk_buff *skb2 = skb_copy_expand(skb,
>> - overhead, 0, flags);
>> - dev_kfree_skb_any(skb);
>> - skb = skb2;
>> - if (!skb)
>> - return NULL;
>> + /* Make writable and expand space by overhead if required */
>> + if (skb_cow(skb, overhead)) {
>> + return NULL;
>> }
>
> Note that this patch will probably force a copy of all locally generated
> TCP packets.
>
> For them skb_cloned(skb) is true.
>
> I do believe skb_cow_head() would be better, since TCP stack uses the
> __skb_header_release() helper to tell lower stacks they can write the
> header part, even on a clone.
Agreed.
