skbuff: Fix skb checksum partial check.

[ Upstream commit 31b33dfb0a144469dd805514c9e63f4993729a48 ]

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@odin.com>
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index cd3cbd4..d0c9e6d 100644 (file)
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2046,7 +2046,7 @@ 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 7121d9b..b30d9c2 100644 (file)
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2579,11 +2579,12 @@ EXPORT_SYMBOL(skb_append_datato_frags);
  */
 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);