[PATCH 57/64] netfilter: conntrack: Use struct_group() to zero struct nf_conn

[Kees Cook]

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

Replace the empty __nfct_init_offset member with a struct_group() to
mark the region of struct nf_conn that should be initialized to zero,
allowing memset() to correctly reason about the size of the write.

Signed-off-by: Kees Cook <keesc...@chromium.org>
---
 include/net/netfilter/nf_conntrack.h | 20 ++++++++++----------
 net/netfilter/nf_conntrack_core.c    |  4 +---
 2 files changed, 11 insertions(+), 13 deletions(-)

diff --git a/include/net/netfilter/nf_conntrack.h 
b/include/net/netfilter/nf_conntrack.h
index cc663c68ddc4..51004fce2937 100644
--- a/include/net/netfilter/nf_conntrack.h
+++ b/include/net/netfilter/nf_conntrack.h
@@ -101,24 +101,24 @@ struct nf_conn {
        struct hlist_node       nat_bysource;
 #endif
        /* all members below initialized via memset */
-       struct { } __nfct_init_offset;
-
-       /* If we were expected by an expectation, this will be it */
-       struct nf_conn *master;
+       struct_group(init,
+               /* If we were expected by an expectation, this will be it */
+               struct nf_conn *master;
 
 #if defined(CONFIG_NF_CONNTRACK_MARK)
-       u_int32_t mark;
+               u_int32_t mark;
 #endif
 
 #ifdef CONFIG_NF_CONNTRACK_SECMARK
-       u_int32_t secmark;
+               u_int32_t secmark;
 #endif
 
-       /* Extensions */
-       struct nf_ct_ext *ext;
+               /* Extensions */
+               struct nf_ct_ext *ext;
 
-       /* Storage reserved for other modules, must be the last member */
-       union nf_conntrack_proto proto;
+               /* Storage reserved for other modules, must be the last member 
*/
+               union nf_conntrack_proto proto;
+       );
 };
 
 static inline struct nf_conn *
diff --git a/net/netfilter/nf_conntrack_core.c 
b/net/netfilter/nf_conntrack_core.c
index 5c03e5106751..b05eb64ec788 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -1527,9 +1527,7 @@ __nf_conntrack_alloc(struct net *net,
        ct->status = 0;
        ct->timeout = 0;
        write_pnet(&ct->ct_net, net);
-       memset(&ct->__nfct_init_offset, 0,
-              offsetof(struct nf_conn, proto) -
-              offsetof(struct nf_conn, __nfct_init_offset));
+       memset(&ct->init, 0, sizeof(ct->init));
 
        nf_ct_zone_add(ct, zone);
 
-- 
2.30.2