net: Fix possible wrong checksum generation.

Patch cef401de7be8c4e (net: fix possible wrong checksum
generation) fixed wrong checksum calculation but it broke TSO by
defining new GSO type but not a netdev feature for that type.
net_gso_ok() would not allow hardware checksum/segmentation
offload of such packets without the feature.

Following patch fixes TSO and wrong checksum. This patch uses
same logic that Eric Dumazet used. Patch introduces new flag
SKBTX_SHARED_FRAG if at least one frag can be modified by
the user. but SKBTX_SHARED_FRAG flag is kept in skb shared
info tx_flags rather than gso_type.

tx_flags is better compared to gso_type since we can have skb with
shared frag without gso packet. It does not link SHARED_FRAG to
GSO, So there is no need to define netdev feature for this.

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

1 files changed, 9 insertions, 8 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index d7573c37a51d..9da99520ccd5 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -230,6 +230,13 @@ enum {
 
         /* generate wifi status information (where possible) */
         SKBTX_WIFI_STATUS = 1 << 4,
+
+        /* This indicates at least one fragment might be overwritten
+         * (as in vmsplice(), sendfile() ...)
+         * If we need to compute a TX checksum, we'll need to copy
+         * all frags to avoid possible bad checksum
+         */
+        SKBTX_SHARED_FRAG = 1 << 5,
 };
 
 /*
@@ -307,13 +314,6 @@ enum {
         SKB_GSO_TCPV6 = 1 << 4,
 
         SKB_GSO_FCOE = 1 << 5,
-
-        /* This indicates at least one fragment might be overwritten
-         * (as in vmsplice(), sendfile() ...)
-         * If we need to compute a TX checksum, we'll need to copy
-         * all frags to avoid possible bad checksum
-         */
-        SKB_GSO_SHARED_FRAG = 1 << 6,
 };
 
 #if BITS_PER_LONG > 32
@@ -2220,7 +2220,8 @@ static inline int skb_linearize(struct sk_buff *skb)
  */
 static inline bool skb_has_shared_frag(const struct sk_buff *skb)
 {
-        return skb_shinfo(skb)->gso_type & SKB_GSO_SHARED_FRAG;
+        return skb_is_nonlinear(skb) &&
+               skb_shinfo(skb)->tx_flags & SKBTX_SHARED_FRAG;
 }
 
 /**