[PATCH v2 40/63] netfilter: conntrack: Use memset_startat() 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.

Use memset_startat() to avoid confusing memset() about writing beyond
the target struct member.

Cc: Pablo Neira Ayuso <pablo at netfilter.org>
Cc: Jozsef Kadlecsik <kadlec at netfilter.org>
Cc: Florian Westphal <fw at strlen.de>
Cc: "David S. Miller" <davem at davemloft.net>
Cc: Jakub Kicinski <kuba at kernel.org>
Cc: netfilter-devel at vger.kernel.org
Cc: coreteam at netfilter.org
Cc: netdev at vger.kernel.org
Signed-off-by: Kees Cook <keescook at chromium.org>
---
 net/netfilter/nf_conntrack_core.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index d31dbccbe7bd..060503230519 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -1500,9 +1500,7 @@ __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_after(ct, 0, __nfct_init_offset);
 
 	nf_ct_zone_add(ct, zone);
 
-- 
2.30.2