udplite: fix partial checksum initialization

Since UDP-Lite is always using checksum, the following path is
triggered when calculating pseudo header for it:

  udp4_csum_init() or udp6_csum_init()
    skb_checksum_init_zero_check()
      __skb_checksum_validate_complete()

The problem can appear if skb->len is less than CHECKSUM_BREAK. In
this particular case __skb_checksum_validate_complete() also invokes
__skb_checksum_complete(skb). If UDP-Lite is using partial checksum
that covers only part of a packet, the function will return bad
checksum and the packet will be dropped.

It can be fixed if we skip skb_checksum_init_zero_check() and only
set the required pseudo header checksum for UDP-Lite with partial
checksum before udp4_csum_init()/udp6_csum_init() functions return.

Fixes: ed70fcfcee95 ("net: Call skb_checksum_init in IPv4")
Fixes: e4f45b7f40bd ("net: Call skb_checksum_init in IPv6")
Signed-off-by: Alexey Kodanev <alexey.kodanev@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 11 insertions, 0 deletions

diff --git a/include/net/udplite.h b/include/net/udplite.h
index 81bdbf97319b..9185e45b997f 100644
--- a/include/net/udplite.h
+++ b/include/net/udplite.h
@@ -64,6 +64,7 @@ static inline int udplite_checksum_init(struct sk_buff *skb, struct udphdr *uh)
                 UDP_SKB_CB(skb)->cscov = cscov;
                 if (skb->ip_summed == CHECKSUM_COMPLETE)
                         skb->ip_summed = CHECKSUM_NONE;
+                skb->csum_valid = 0;
         }
 
         return 0;
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index bfaefe560b5c..e5ef7c38c934 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -2024,6 +2024,11 @@ static inline int udp4_csum_init(struct sk_buff *skb, struct udphdr *uh,
                 err = udplite_checksum_init(skb, uh);
                 if (err)
                         return err;
+
+                if (UDP_SKB_CB(skb)->partial_cov) {
+                        skb->csum = inet_compute_pseudo(skb, proto);
+                        return 0;
+                }
         }
 
         /* Note, we are only interested in != 0 or == 0, thus the
diff --git a/net/ipv6/ip6_checksum.c b/net/ipv6/ip6_checksum.c
index ec43d18b5ff9..547515e8450a 100644
--- a/net/ipv6/ip6_checksum.c
+++ b/net/ipv6/ip6_checksum.c
@@ -73,6 +73,11 @@ int udp6_csum_init(struct sk_buff *skb, struct udphdr *uh, int proto)
                 err = udplite_checksum_init(skb, uh);
                 if (err)
                         return err;
+
+                if (UDP_SKB_CB(skb)->partial_cov) {
+                        skb->csum = ip6_compute_pseudo(skb, proto);
+                        return 0;
+                }
         }
 
         /* To support RFC 6936 (allow zero checksum in UDP/IPV6 for tunnels)