4 files changed, 16 insertions, 8 deletions

diff --git a/include/net/ip.h b/include/net/ip.h
index 4aa781b7f609..b885d75cede4 100644
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -266,7 +266,8 @@ int ip_dont_fragment(struct sock *sk, struct dst_entry *dst)
 
 static inline bool ip_sk_accept_pmtu(const struct sock *sk)
 {
-        return inet_sk(sk)->pmtudisc != IP_PMTUDISC_INTERFACE;
+        return inet_sk(sk)->pmtudisc != IP_PMTUDISC_INTERFACE &&
+               inet_sk(sk)->pmtudisc != IP_PMTUDISC_OMIT;
 }
 
 static inline bool ip_sk_use_pmtu(const struct sock *sk)
@@ -274,6 +275,12 @@ static inline bool ip_sk_use_pmtu(const struct sock *sk)
         return inet_sk(sk)->pmtudisc < IP_PMTUDISC_PROBE;
 }
 
+static inline bool ip_sk_local_df(const struct sock *sk)
+{
+        return inet_sk(sk)->pmtudisc < IP_PMTUDISC_DO ||
+               inet_sk(sk)->pmtudisc == IP_PMTUDISC_OMIT;
+}
+
 static inline unsigned int ip_dst_mtu_maybe_forward(const struct dst_entry *dst,
                                                     bool forwarding)
 {
diff --git a/include/uapi/linux/in.h b/include/uapi/linux/in.h
index 393c5de09d42..c33a65e3d62c 100644
--- a/include/uapi/linux/in.h
+++ b/include/uapi/linux/in.h
@@ -120,6 +120,10 @@ struct in_addr {
  * this socket to prevent accepting spoofed ones.
  */
 #define IP_PMTUDISC_INTERFACE           4
+/* weaker version of IP_PMTUDISC_INTERFACE, which allos packets to get
+ * fragmented if they exeed the interface mtu
+ */
+#define IP_PMTUDISC_OMIT                5
 
 #define IP_MULTICAST_IF                 32
 #define IP_MULTICAST_TTL                33
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 22aa11971ed1..e85445b2b102 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -824,8 +824,7 @@ static int __ip_append_data(struct sock *sk,
 
         fragheaderlen = sizeof(struct iphdr) + (opt ? opt->optlen : 0);
         maxfraglen = ((mtu - fragheaderlen) & ~7) + fragheaderlen;
-        maxnonfragsize = (inet->pmtudisc >= IP_PMTUDISC_DO) ?
-                         mtu : 0xFFFF;
+        maxnonfragsize = ip_sk_local_df(sk) ? 0xFFFF : mtu;
 
         if (cork->length + length > maxnonfragsize - fragheaderlen) {
                 ip_local_error(sk, EMSGSIZE, fl4->daddr, inet->inet_dport,
@@ -1148,8 +1147,7 @@ ssize_t	ip_append_page(struct sock *sk, struct flowi4 *fl4, struct page *page,
 
         fragheaderlen = sizeof(struct iphdr) + (opt ? opt->optlen : 0);
         maxfraglen = ((mtu - fragheaderlen) & ~7) + fragheaderlen;
-        maxnonfragsize = (inet->pmtudisc >= IP_PMTUDISC_DO) ?
-                         mtu : 0xFFFF;
+        maxnonfragsize = ip_sk_local_df(sk) ? 0xFFFF : mtu;
 
         if (cork->length + size > maxnonfragsize - fragheaderlen) {
                 ip_local_error(sk, EMSGSIZE, fl4->daddr, inet->inet_dport,
@@ -1310,8 +1308,7 @@ struct sk_buff *__ip_make_skb(struct sock *sk,
          * to fragment the frame generated here. No matter, what transforms
          * how transforms change size of the packet, it will come out.
          */
-        if (inet->pmtudisc < IP_PMTUDISC_DO)
-                skb->local_df = 1;
+        skb->local_df = ip_sk_local_df(sk);
 
         /* DF bit is set when we want to see DF on outgoing frames.
          * If local_df is set too, we still allow to fragment this frame
diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index 0968b28c4cf3..64741b938632 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -643,7 +643,7 @@ static int do_ip_setsockopt(struct sock *sk, int level,
                 inet->nodefrag = val ? 1 : 0;
                 break;
         case IP_MTU_DISCOVER:
-                if (val < IP_PMTUDISC_DONT || val > IP_PMTUDISC_INTERFACE)
+                if (val < IP_PMTUDISC_DONT || val > IP_PMTUDISC_OMIT)
                         goto e_inval;
                 inet->pmtudisc = val;
                 break;