ipv6: Select fragment id during UFO segmentation if not set. [Linux 3.16.72]

This Linux kernel change "ipv6: Select fragment id during UFO segmentation if not set" is included in the Linux 3.16.72 release. This change is authored by Vlad Yasevich <vyasevich [at] gmail.com> on Tue Feb 3 16:36:15 2015 -0500. The commit for this change in Linux stable tree is 2e095ca (patch) which is from upstream commit 0508c07. The same Linux upstream change may have been applied to various maintained Linux releases and you can find all Linux releases containing changes from upstream 0508c07.

ipv6: Select fragment id during UFO segmentation if not set.

commit 0508c07f5e0c94f38afd5434e8b2a55b84553077 upstream.

If the IPv6 fragment id has not been set and we perform
fragmentation due to UFO, select a new fragment id.
We now consider a fragment id of 0 as unset and if id selection
process returns 0 (after all the pertrubations), we set it to
0x80000000, thus giving us ample space not to create collisions
with the next packet we may have to fragment.

When doing UFO integrity checking, we also select the
fragment id if it has not be set yet.   This is stored into
the skb_shinfo() thus allowing UFO to function correclty.

This patch also removes duplicate fragment id generation code
and moves ipv6_select_ident() into the header as it may be
used during GSO.

Signed-off-by: Vladislav Yasevich <vyasevic@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

There are 68 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 include/net/ipv6.h     |  3 +++
 net/ipv6/ip6_output.c  | 14 --------------
 net/ipv6/output_core.c | 41 +++++++++++++++++++++++++++++++++++------
 net/ipv6/udp_offload.c | 10 +++++++++-
 4 files changed, 47 insertions(+), 21 deletions(-)

diff --git a/include/net/ipv6.h b/include/net/ipv6.h
index c30ba46..209d096 100644
--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -688,6 +688,9 @@ static inline int ipv6_addr_diff(const struct in6_addr *a1, const struct in6_add
    return __ipv6_addr_diff(a1, a2, sizeof(struct in6_addr));
 }

+u32 __ipv6_select_ident(u32 hashrnd, struct in6_addr *dst,
+           struct in6_addr *src);
+void ipv6_select_ident(struct frag_hdr *fhdr, struct rt6_info *rt);
 void ipv6_proxy_select_ident(struct sk_buff *skb);

 int ip6_dst_hoplimit(struct dst_entry *dst);
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index e59b300..6780c45 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -538,20 +538,6 @@ static void ip6_copy_metadata(struct sk_buff *to, struct sk_buff *from)
    skb_copy_secmark(to, from);
 }

-static void ipv6_select_ident(struct frag_hdr *fhdr, struct rt6_info *rt)
-{
-   static u32 ip6_idents_hashrnd __read_mostly;
-   u32 hash, id;
-
-   net_get_random_once(&ip6_idents_hashrnd, sizeof(ip6_idents_hashrnd));
-
-   hash = __ipv6_addr_jhash(&rt->rt6i_dst.addr, ip6_idents_hashrnd);
-   hash = __ipv6_addr_jhash(&rt->rt6i_src.addr, hash);
-
-   id = ip_idents_reserve(hash, 1);
-   fhdr->identification = htonl(id);
-}
-
 int ip6_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
 {
    struct sk_buff *frag;
diff --git a/net/ipv6/output_core.c b/net/ipv6/output_core.c
index e32c1ff..6bacd3b 100644
--- a/net/ipv6/output_core.c
+++ b/net/ipv6/output_core.c
@@ -9,6 +9,24 @@
 #include <net/addrconf.h>
 #include <net/secure_seq.h>

+u32 __ipv6_select_ident(u32 hashrnd, struct in6_addr *dst, struct in6_addr *src)
+{
+   u32 hash, id;
+
+   hash = __ipv6_addr_jhash(dst, hashrnd);
+   hash = __ipv6_addr_jhash(src, hash);
+
+   /* Treat id of 0 as unset and if we get 0 back from ip_idents_reserve,
+    * set the hight order instead thus minimizing possible future
+    * collisions.
+    */
+   id = ip_idents_reserve(hash, 1);
+   if (unlikely(!id))
+       id = 1 << 31;
+
+   return id;
+}
+
 /* This function exists only for tap drivers that must support broken
  * clients requesting UFO without specifying an IPv6 fragment ID.
  *
@@ -22,7 +40,7 @@ void ipv6_proxy_select_ident(struct sk_buff *skb)
    static u32 ip6_proxy_idents_hashrnd __read_mostly;
    struct in6_addr buf[2];
    struct in6_addr *addrs;
-   u32 hash, id;
+   u32 id;

    addrs = skb_header_pointer(skb,
                   skb_network_offset(skb) +
@@ -34,14 +52,25 @@ void ipv6_proxy_select_ident(struct sk_buff *skb)
    net_get_random_once(&ip6_proxy_idents_hashrnd,
                sizeof(ip6_proxy_idents_hashrnd));

-   hash = __ipv6_addr_jhash(&addrs[1], ip6_proxy_idents_hashrnd);
-   hash = __ipv6_addr_jhash(&addrs[0], hash);
-
-   id = ip_idents_reserve(hash, 1);
-   skb_shinfo(skb)->ip6_frag_id = htonl(id);
+   id = __ipv6_select_ident(ip6_proxy_idents_hashrnd,
+                &addrs[1], &addrs[0]);
+   skb_shinfo(skb)->ip6_frag_id = id;
 }
 EXPORT_SYMBOL_GPL(ipv6_proxy_select_ident);

+void ipv6_select_ident(struct frag_hdr *fhdr, struct rt6_info *rt)
+{
+   static u32 ip6_idents_hashrnd __read_mostly;
+   u32 id;
+
+   net_get_random_once(&ip6_idents_hashrnd, sizeof(ip6_idents_hashrnd));
+
+   id = __ipv6_select_ident(ip6_idents_hashrnd, &rt->rt6i_dst.addr,
+                &rt->rt6i_src.addr);
+   fhdr->identification = htonl(id);
+}
+EXPORT_SYMBOL(ipv6_select_ident);
+
 int ip6_find_1stfragopt(struct sk_buff *skb, u8 **nexthdr)
 {
    unsigned int offset = sizeof(struct ipv6hdr);
diff --git a/net/ipv6/udp_offload.c b/net/ipv6/udp_offload.c
index fa9ea1a..8f121a5 100644
--- a/net/ipv6/udp_offload.c
+++ b/net/ipv6/udp_offload.c
@@ -75,6 +75,10 @@ static struct sk_buff *udp6_ufo_fragment(struct sk_buff *skb,

        skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(skb->len, mss);

+       /* Set the IPv6 fragment id if not set yet */
+       if (!skb_shinfo(skb)->ip6_frag_id)
+           ipv6_proxy_select_ident(skb);
+
        segs = NULL;
        goto out;
    }
@@ -120,7 +124,11 @@ static struct sk_buff *udp6_ufo_fragment(struct sk_buff *skb,
        fptr = (struct frag_hdr *)(skb_network_header(skb) + unfrag_ip6hlen);
        fptr->nexthdr = nexthdr;
        fptr->reserved = 0;
-       fptr->identification = skb_shinfo(skb)->ip6_frag_id;
+       if (skb_shinfo(skb)->ip6_frag_id)
+           fptr->identification = skb_shinfo(skb)->ip6_frag_id;
+       else
+           ipv6_select_ident(fptr,
+                     (struct rt6_info *)skb_dst(skb));

        /* Fragment the skb. ipv6 header and the remaining fields of the
         * fragment header are updated in ipv6_gso_segment()

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