skbuff: Fix skb checksum partial check.

Earlier patch 6376d0990 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: 6376d0990 ("skbuff: Fix skb checksum flag on skb pull")
Reported-by: Andrew Vagin <avagin@odin.com>
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 2b0a30a6e31cf780fd8fcf11b7857b45b5c86bee..4398411236f16c3f87691162909dc6197fb62b08 100644 (file)
--- 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 dad4dd37e2aaad17b9493cb67796ed9650515a84..fab4599ba8b261dc43977af8349a336edc4d2799 100644 (file)
--- 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;
 }
 EXPORT_SYMBOL_GPL(skb_pull_rcsum);