[NET]: Detect hardware rx checksum faults correctly

Here is the patch that introduces the generic skb_checksum_complete
which also checks for hardware RX checksum faults.  If that happens,
it'll call netdev_rx_csum_fault which currently prints out a stack
trace with the device name.  In future it can turn off RX checksum.

I've converted every spot under net/ that does RX checksum checks to
use skb_checksum_complete or __skb_checksum_complete with the
exceptions of:

* Those places where checksums are done bit by bit.  These will call
netdev_rx_csum_fault directly.

* The following have not been completely checked/converted:

ipmr
ip_vs
netfilter
dccp

This patch is based on patches and suggestions from Stephen Hemminger
and David S. Miller.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

19 files changed, 173 insertions, 134 deletions

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index c6efce4a04a4..936f8b76114e 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -927,6 +927,13 @@ extern int		netdev_max_backlog;
 extern int              weight_p;
 extern int              netdev_set_master(struct net_device *dev, struct net_device *master);
 extern int skb_checksum_help(struct sk_buff *skb, int inward);
+#ifdef CONFIG_BUG
+extern void netdev_rx_csum_fault(struct net_device *dev);
+#else
+static inline void netdev_rx_csum_fault(struct net_device *dev)
+{
+}
+#endif
 /* rx skb timestamps */
 extern void             net_enable_timestamp(void);
 extern void             net_disable_timestamp(void);
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 83010231db99..0a8ea8b35816 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1236,8 +1236,7 @@ extern unsigned int    datagram_poll(struct file *file, struct socket *sock,
 extern int             skb_copy_datagram_iovec(const struct sk_buff *from,
                                                int offset, struct iovec *to,
                                                int size);
-extern int             skb_copy_and_csum_datagram_iovec(const
-                                                        struct sk_buff *skb,
+extern int             skb_copy_and_csum_datagram_iovec(struct sk_buff *skb,
                                                         int hlen,
                                                         struct iovec *iov);
 extern void            skb_free_datagram(struct sock *sk, struct sk_buff *skb);
@@ -1305,6 +1304,30 @@ static inline void skb_set_timestamp(struct sk_buff *skb, const struct timeval *
 
 extern void __net_timestamp(struct sk_buff *skb);
 
+extern unsigned int __skb_checksum_complete(struct sk_buff *skb);
+
+/**
+ *      skb_checksum_complete - Calculate checksum of an entire packet
+ *      @skb: packet to process
+ *
+ *      This function calculates the checksum over the entire packet plus
+ *      the value of skb->csum.  The latter can be used to supply the
+ *      checksum of a pseudo header as used by TCP/UDP.  It returns the
+ *      checksum.
+ *
+ *      For protocols that contain complete checksums such as ICMP/TCP/UDP,
+ *      this function can be used to verify that checksum on received
+ *      packets.  In that case the function should return zero if the
+ *      checksum is correct.  In particular, this function will return zero
+ *      if skb->ip_summed is CHECKSUM_UNNECESSARY which indicates that the
+ *      hardware has already verified the correctness of the checksum.
+ */
+static inline unsigned int skb_checksum_complete(struct sk_buff *skb)
+{
+        return skb->ip_summed != CHECKSUM_UNNECESSARY &&
+                __skb_checksum_complete(skb);
+}
+
 #ifdef CONFIG_NETFILTER
 static inline void nf_conntrack_put(struct nf_conntrack *nfct)
 {
diff --git a/include/net/tcp.h b/include/net/tcp.h
index c24339c4e310..96cc3b434e40 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -27,6 +27,7 @@
 #include <linux/slab.h>
 #include <linux/cache.h>
 #include <linux/percpu.h>
+#include <linux/skbuff.h>
 
 #include <net/inet_connection_sock.h>
 #include <net/inet_timewait_sock.h>
@@ -852,7 +853,7 @@ static __inline__ u16 tcp_v4_check(struct tcphdr *th, int len,
 
 static __inline__ int __tcp_checksum_complete(struct sk_buff *skb)
 {
-        return (unsigned short)csum_fold(skb_checksum(skb, 0, skb->len, skb->csum));
+        return __skb_checksum_complete(skb);
 }
 
 static __inline__ int tcp_checksum_complete(struct sk_buff *skb)
diff --git a/net/core/datagram.c b/net/core/datagram.c
index d219435d086c..1bcfef51ac58 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -350,6 +350,20 @@ fault:
         return -EFAULT;
 }
 
+unsigned int __skb_checksum_complete(struct sk_buff *skb)
+{
+        unsigned int sum;
+
+        sum = (u16)csum_fold(skb_checksum(skb, 0, skb->len, skb->csum));
+        if (likely(!sum)) {
+                if (unlikely(skb->ip_summed == CHECKSUM_HW))
+                        netdev_rx_csum_fault(skb->dev);
+                skb->ip_summed = CHECKSUM_UNNECESSARY;
+        }
+        return sum;
+}
+EXPORT_SYMBOL(__skb_checksum_complete);
+
 /**
  *      skb_copy_and_csum_datagram_iovec - Copy and checkum skb to user iovec.
  *      @skb: skbuff
@@ -363,7 +377,7 @@ fault:
  *               -EFAULT - fault during copy. Beware, in this case iovec
  *                         can be modified!
  */
-int skb_copy_and_csum_datagram_iovec(const struct sk_buff *skb,
+int skb_copy_and_csum_datagram_iovec(struct sk_buff *skb,
                                      int hlen, struct iovec *iov)
 {
         unsigned int csum;
@@ -376,8 +390,7 @@ int skb_copy_and_csum_datagram_iovec(const struct sk_buff *skb,
                 iov++;
 
         if (iov->iov_len < chunk) {
-                if ((unsigned short)csum_fold(skb_checksum(skb, 0, chunk + hlen,
-                                                           skb->csum)))
+                if (__skb_checksum_complete(skb))
                         goto csum_error;
                 if (skb_copy_datagram_iovec(skb, hlen, iov, chunk))
                         goto fault;
@@ -388,6 +401,8 @@ int skb_copy_and_csum_datagram_iovec(const struct sk_buff *skb,
                         goto fault;
                 if ((unsigned short)csum_fold(csum))
                         goto csum_error;
+                if (unlikely(skb->ip_summed == CHECKSUM_HW))
+                        netdev_rx_csum_fault(skb->dev);
                 iov->iov_len -= chunk;
                 iov->iov_base += chunk;
         }
diff --git a/net/core/dev.c b/net/core/dev.c
index 8d1541595277..0b48e294aafe 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1108,6 +1108,18 @@ out:
         return ret;
 }
 
+/* Take action when hardware reception checksum errors are detected. */
+#ifdef CONFIG_BUG
+void netdev_rx_csum_fault(struct net_device *dev)
+{
+        if (net_ratelimit()) {
+                printk(KERN_ERR "%s: hw csum failure.\n", dev->name);
+                dump_stack();
+        }