udp: fix IP_CHECKSUM handling

First bug was added in commit ad6f939ab193 ("ip: Add offset parameter to
ip_cmsg_recv") : Tom missed that ipv4 udp messages could be received on
AF_INET6 socket. ip_cmsg_recv(msg, skb) should have been replaced by
ip_cmsg_recv_offset(msg, skb, sizeof(struct udphdr));

Then commit e6afc8ace6dd ("udp: remove headers from UDP packets before
queueing") forgot to adjust the offsets now UDP headers are pulled
before skb are put in receive queue.

Fixes: ad6f939ab193 ("ip: Add offset parameter to ip_cmsg_recv")
Fixes: e6afc8ace6dd ("udp: remove headers from UDP packets before queueing")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Sam Kumar <samanthakumar@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Tested-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

4 files changed, 11 insertions, 9 deletions

diff --git a/include/net/ip.h b/include/net/ip.h
index c9d07988911e..5413883ac47f 100644
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -578,7 +578,7 @@ int ip_options_rcv_srr(struct sk_buff *skb);
  */
 
 void ipv4_pktinfo_prepare(const struct sock *sk, struct sk_buff *skb);
-void ip_cmsg_recv_offset(struct msghdr *msg, struct sk_buff *skb, int offset);
+void ip_cmsg_recv_offset(struct msghdr *msg, struct sk_buff *skb, int tlen, int offset);
 int ip_cmsg_send(struct sock *sk, struct msghdr *msg,
                  struct ipcm_cookie *ipc, bool allow_ipv6);
 int ip_setsockopt(struct sock *sk, int level, int optname, char __user *optval,
@@ -600,7 +600,7 @@ void ip_local_error(struct sock *sk, int err, __be32 daddr, __be16 dport,
 
 static inline void ip_cmsg_recv(struct msghdr *msg, struct sk_buff *skb)
 {
-        ip_cmsg_recv_offset(msg, skb, 0);
+        ip_cmsg_recv_offset(msg, skb, 0, 0);
 }
 
 bool icmp_global_allow(void);
diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index af4919792b6a..b8a2d63d1fb8 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -98,7 +98,7 @@ static void ip_cmsg_recv_retopts(struct msghdr *msg, struct sk_buff *skb)
 }
 
 static void ip_cmsg_recv_checksum(struct msghdr *msg, struct sk_buff *skb,
-                                  int offset)
+                                  int tlen, int offset)
 {
         __wsum csum = skb->csum;
 
@@ -106,8 +106,9 @@ static void ip_cmsg_recv_checksum(struct msghdr *msg, struct sk_buff *skb,
                 return;
 
         if (offset != 0)
-                csum = csum_sub(csum, csum_partial(skb_transport_header(skb),
-                                                   offset, 0));
+                csum = csum_sub(csum,
+                                csum_partial(skb_transport_header(skb) + tlen,
+                                             offset, 0));
 
         put_cmsg(msg, SOL_IP, IP_CHECKSUM, sizeof(__wsum), &csum);
 }
@@ -153,7 +154,7 @@ static void ip_cmsg_recv_dstaddr(struct msghdr *msg, struct sk_buff *skb)
 }
 
 void ip_cmsg_recv_offset(struct msghdr *msg, struct sk_buff *skb,
-                         int offset)
+                         int tlen, int offset)
 {
         struct inet_sock *inet = inet_sk(skb->sk);
         unsigned int flags = inet->cmsg_flags;
@@ -216,7 +217,7 @@ void ip_cmsg_recv_offset(struct msghdr *msg, struct sk_buff *skb,
         }
 
         if (flags & IP_CMSG_CHECKSUM)
-                ip_cmsg_recv_checksum(msg, skb, offset);
+                ip_cmsg_recv_checksum(msg, skb, tlen, offset);
 }
 EXPORT_SYMBOL(ip_cmsg_recv_offset);
 
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 311613e413cb..d123d68f4d1d 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1322,7 +1322,7 @@ try_again:
                 *addr_len = sizeof(*sin);
         }
         if (inet->cmsg_flags)
-                ip_cmsg_recv_offset(msg, skb, sizeof(struct udphdr) + off);
+                ip_cmsg_recv_offset(msg, skb, sizeof(struct udphdr), off);
 
         err = copied;
         if (flags & MSG_TRUNC)
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 9aa7c1c7a9ce..b2ef061e6836 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -427,7 +427,8 @@ try_again:
 
         if (is_udp4) {
                 if (inet->cmsg_flags)
-                        ip_cmsg_recv(msg, skb);
+                        ip_cmsg_recv_offset(msg, skb,
+                                            sizeof(struct udphdr), off);
         } else {
                 if (np->rxopt.all)
                         ip6_datagram_recv_specific_ctl(sk, msg, skb);