[ovs-dev] [PATCH] datapath: Backport: skbuff: Fix skb checksum partial check.

[Pravin B Shelar]

This bug fix is not required for OVS use cases. But is it
nice to keep function consistent with upstream implementation.

Upstream commit:

    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 <avagin at odin.com>
    Signed-off-by: Pravin B Shelar <pshelar at nicira.com>
    Signed-off-by: David S. Miller <davem at davemloft.net>

Upstream: 31b33dfb0a1 ("skbuff: Fix skb checksum partial check");
Signed-off-by: Pravin B Shelar <pshelar at nicira.com>
---
 datapath/linux/compat/include/linux/skbuff.h | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/datapath/linux/compat/include/linux/skbuff.h b/datapath/linux/compat/include/linux/skbuff.h
index 0edcbfd..ab54a83 100644
--- a/datapath/linux/compat/include/linux/skbuff.h
+++ b/datapath/linux/compat/include/linux/skbuff.h
@@ -371,18 +371,19 @@ 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;
 }
 
 #define skb_pull_rcsum rpl_skb_pull_rcsum
 static inline 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;
 }
 
 #endif
-- 
1.8.3.1