In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memset(), avoid intentionally writing across
neighboring fields.

Add struct_group() to mark region of struct rt6_info that should be
initialized to zero.

Signed-off-by: Kees Cook <keesc...@chromium.org>
---
 include/net/ip6_fib.h | 30 ++++++++++++++++--------------
 net/ipv6/route.c      |  4 +---
 2 files changed, 17 insertions(+), 17 deletions(-)

diff --git a/include/net/ip6_fib.h b/include/net/ip6_fib.h
index 15b7fbe6b15c..9816e7444918 100644
--- a/include/net/ip6_fib.h
+++ b/include/net/ip6_fib.h
@@ -205,20 +205,22 @@ struct fib6_info {
 
 struct rt6_info {
        struct dst_entry                dst;
-       struct fib6_info __rcu          *from;
-       int                             sernum;
-
-       struct rt6key                   rt6i_dst;
-       struct rt6key                   rt6i_src;
-       struct in6_addr                 rt6i_gateway;
-       struct inet6_dev                *rt6i_idev;
-       u32                             rt6i_flags;
-
-       struct list_head                rt6i_uncached;
-       struct uncached_list            *rt6i_uncached_list;
-
-       /* more non-fragment space at head required */
-       unsigned short                  rt6i_nfheader_len;
+       struct_group(init,
+               struct fib6_info __rcu          *from;
+               int                             sernum;
+
+               struct rt6key                   rt6i_dst;
+               struct rt6key                   rt6i_src;
+               struct in6_addr                 rt6i_gateway;
+               struct inet6_dev                *rt6i_idev;
+               u32                             rt6i_flags;
+
+               struct list_head                rt6i_uncached;
+               struct uncached_list            *rt6i_uncached_list;
+
+               /* more non-fragment space at head required */
+               unsigned short                  rt6i_nfheader_len;
+       );
 };
 
 struct fib6_result {
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 6b8051106aba..bbcc605bab57 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -327,9 +327,7 @@ static const struct rt6_info ip6_blk_hole_entry_template = {
 
 static void rt6_info_init(struct rt6_info *rt)
 {
-       struct dst_entry *dst = &rt->dst;
-
-       memset(dst + 1, 0, sizeof(*rt) - sizeof(*dst));
+       memset(&rt->init, 0, sizeof(rt->init));
        INIT_LIST_HEAD(&rt->rt6i_uncached);
 }
 
-- 
2.30.2

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