net: Preserve CHECKSUM_COMPLETE at validation

Currently when the first checksum in a packet is validated using
CHECKSUM_COMPLETE, ip_summed is overwritten to be CHECKSUM_UNNECESSARY
so that any subsequent checksums in the packet are not correctly
validated.

This patch adds csum_valid flag in sk_buff and uses that to indicate
validated checksum instead of setting CHECKSUM_UNNECESSARY. The bit
is set accordingly in the skb_checksum_validate_* functions. The flag
is checked in skb_checksum_complete, so that validation is communicated
between checksum_init and checksum_complete sequence in TCP and UDP.

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 14 insertions, 9 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 1f50bfe2243d..72a53805858a 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -572,7 +572,8 @@ struct sk_buff {
          */
         __u8                    encapsulation:1;
         __u8                    encap_hdr_csum:1;
-        /* 5/7 bit hole (depending on ndisc_nodetype presence) */
+        __u8                    csum_valid:1;
+        /* 4/6 bit hole (depending on ndisc_nodetype presence) */
         kmemcheck_bitfield_end(flags2);
 
 #if defined CONFIG_NET_DMA || defined CONFIG_NET_RX_BUSY_POLL
@@ -2735,7 +2736,7 @@ __sum16 __skb_checksum_complete(struct sk_buff *skb);
 
 static inline int skb_csum_unnecessary(const struct sk_buff *skb)
 {
-        return skb->ip_summed & CHECKSUM_UNNECESSARY;
+        return ((skb->ip_summed & CHECKSUM_UNNECESSARY) || skb->csum_valid);
 }
 
 /**
@@ -2769,10 +2770,8 @@ static inline bool __skb_checksum_validate_needed(struct sk_buff *skb,
                                                   bool zero_okay,
                                                   __sum16 check)
 {
-        if (skb_csum_unnecessary(skb)) {
-                return false;
-        } else if (zero_okay && !check) {
-                skb->ip_summed = CHECKSUM_UNNECESSARY;
+        if (skb_csum_unnecessary(skb) || (zero_okay && !check)) {
+                skb->csum_valid = 1;
                 return false;
         }
 
@@ -2799,15 +2798,20 @@ static inline __sum16 __skb_checksum_validate_complete(struct sk_buff *skb,
 {
         if (skb->ip_summed == CHECKSUM_COMPLETE) {
                 if (!csum_fold(csum_add(psum, skb->csum))) {
-                        skb->ip_summed = CHECKSUM_UNNECESSARY;
+                        skb->csum_valid = 1;
                         return 0;
                 }
         }
 
         skb->csum = psum;
 
-        if (complete || skb->len <= CHECKSUM_BREAK)
-                return __skb_checksum_complete(skb);
+        if (complete || skb->len <= CHECKSUM_BREAK) {
+                __sum16 csum;
+
+                csum = __skb_checksum_complete(skb);
+                skb->csum_valid = !csum;
+                return csum;
+        }
 
         return 0;
 }
@@ -2831,6 +2835,7 @@ static inline __wsum null_compute_pseudo(struct sk_buff *skb, int proto)
                                 zero_okay, check, compute_pseudo)       \
 ({                                                                      \
         __sum16 __ret = 0;                                              \
+        skb->csum_valid = 0;                                            \
         if (__skb_checksum_validate_needed(skb, zero_okay, check))      \
                 __ret = __skb_checksum_validate_complete(skb,           \
                                 complete, compute_pseudo(skb, proto));  \