# \[PATCH v2 40/63\] netfilter: conntrack: Use memset\_startat() to zero struct nf\_conn

- From: Kees Cook \<hidden\>
- Date: 2021-08-18 06:19:38 
- List: linux-block
- Page: https://ratatoskr.run/linux-block/2021/08/1481245
- Thread: https://ratatoskr.run/netfilter-devel/2021/08/1481245/t.md

```text
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@netfilter.org>
Cc: Jozsef Kadlecsik <redacted>
Cc: Florian Westphal <fw@strlen.de>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: <redacted>
Cc: <redacted>
Cc: <redacted>
Signed-off-by: Kees Cook <redacted>
---
 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

```