On Mon, Sep 28, 2015 at 5:46 PM, Tom Herbert <t...@herbertland.com> wrote:
> On Mon, Sep 28, 2015 at 5:24 PM, Pravin B Shelar <pshe...@nicira.com> wrote:
>> Earlier patch 6ae459bda tried to detect void ckecksum partial
>> skb by comparing pull length to checksum offset. But it does
>> not work for all cases since checksum-offset depends on
>> updates to skb->data.
>>
>> Following patch fixes it by validating checksum start offset
>> after skb-data pointer is updated. Negative value of checksum
>> offset start means there is no need to checksum.
>>
>> Fixes: 6ae459bda ("skbuff: Fix skb checksum flag on skb pull")
>> Reported-by: Andrew Vagin <ava...@odin.com>
>> Signed-off-by: Pravin B Shelar <pshe...@nicira.com>
>> ---
>> This and 6ae459bda patches needs to be backported to stable.
>> ---
>> include/linux/skbuff.h | 2 +-
>> net/core/skbuff.c | 9 +++++----
>> 2 files changed, 6 insertions(+), 5 deletions(-)
>>
>> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
>> index 2b0a30a..4398411 100644
>> --- a/include/linux/skbuff.h
>> +++ b/include/linux/skbuff.h
>> @@ -2708,7 +2708,7 @@ static inline void skb_postpull_rcsum(struct sk_buff
>> *skb,
>> if (skb->ip_summed == CHECKSUM_COMPLETE)
>> skb->csum = csum_sub(skb->csum, csum_partial(start, len, 0));
>> else if (skb->ip_summed == CHECKSUM_PARTIAL &&
>> - skb_checksum_start_offset(skb) <= len)
>> + skb_checksum_start_offset(skb) < 0)
>> skb->ip_summed = CHECKSUM_NONE;
>> }
>>
>> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
>> index dad4dd3..fab4599 100644
>> --- a/net/core/skbuff.c
>> +++ b/net/core/skbuff.c
>> @@ -2958,11 +2958,12 @@ EXPORT_SYMBOL_GPL(skb_append_pagefrags);
>> */
>> unsigned char * skb_pull_rcsum(struct sk_buff *skb, unsigned int len)
>> {
>> + unsigned char *data = skb->data;
>> +
>> BUG_ON(len > skb->len);
>> - skb->len -= len;
>> - BUG_ON(skb->len < skb->data_len);
>> - skb_postpull_rcsum(skb, skb->data, len);
>> - return skb->data += len;
>> + __skb_pull(skb, len);
>> + skb_postpull_rcsum(skb, data, len);
>> + return skb->data;
>> }
>
> Nice cleanup in skb_pull_rcsum, but does this affect other calls to
> skb_postpull_rcsum?
>
I checked all callers to skb_postpull_rcsum(). Basically there are two
type of caller. First case is pulling headers which is same as this
case, for example pull skb then call postpull_rcsum() to update csum.
Second case is where update checksum while poping a header, for
example pop vlan header. All these case works fine with the change.
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