ip: generate unique IP identificator if local fragmentation is allowed

If local fragmentation is allowed, then ip_select_ident() and
ip_select_ident_more() need to generate unique IDs to ensure
correct defragmentation on the peer.

For example, if IPsec (tunnel mode) has to encrypt large skbs
that have local_df bit set, then all IP fragments that belonged
to different ESP datagrams would have used the same identificator.
If one of these IP fragments would get lost or reordered, then
peer could possibly stitch together wrong IP fragments that did
not belong to the same datagram. This would lead to a packet loss
or data corruption.

Signed-off-by: Ansis Atteka <aatteka@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 4 deletions

diff --git a/include/net/ip.h b/include/net/ip.h
index 48f55979d842..5e5268807a1c 100644
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -264,9 +264,11 @@ int ip_dont_fragment(struct sock *sk, struct dst_entry *dst)
 
 extern void __ip_select_ident(struct iphdr *iph, struct dst_entry *dst, int more);
 
-static inline void ip_select_ident(struct iphdr *iph, struct dst_entry *dst, struct sock *sk)
+static inline void ip_select_ident(struct sk_buff *skb, struct dst_entry *dst, struct sock *sk)
 {
-        if (iph->frag_off & htons(IP_DF)) {
+        struct iphdr *iph = ip_hdr(skb);
+
+        if ((iph->frag_off & htons(IP_DF)) && !skb->local_df) {
                 /* This is only to work around buggy Windows95/2000
                  * VJ compression implementations.  If the ID field
                  * does not change, they drop every other packet in
@@ -278,9 +280,11 @@ static inline void ip_select_ident(struct iphdr *iph, struct dst_entry *dst, str
                 __ip_select_ident(iph, dst, 0);
 }
 
-static inline void ip_select_ident_more(struct iphdr *iph, struct dst_entry *dst, struct sock *sk, int more)
+static inline void ip_select_ident_more(struct sk_buff *skb, struct dst_entry *dst, struct sock *sk, int more)
 {
-        if (iph->frag_off & htons(IP_DF)) {
+        struct iphdr *iph = ip_hdr(skb);
+
+        if ((iph->frag_off & htons(IP_DF)) && !skb->local_df) {
                 if (sk && inet_sk(sk)->inet_daddr) {
                         iph->id = htons(inet_sk(sk)->inet_id);
                         inet_sk(sk)->inet_id += 1 + more;