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

Kees Cook
2021-07-27T21:16:54Z

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 <keescook@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