linux-hardening - [PATCH 57/64] netfilter: conntrack: Use struct_group() to zero struct nf

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Message-Id: <20210727205855.411487-58-keescook@chromium.org>
Date:   Tue, 27 Jul 2021 13:58:48 -0700
From:   Kees Cook <keescook@...omium.org>
To:     linux-hardening@...r.kernel.org
Cc:     Kees Cook <keescook@...omium.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Keith Packard <keithpac@...zon.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-staging@...ts.linux.dev, linux-block@...r.kernel.org,
        linux-kbuild@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: [PATCH 57/64] netfilter: conntrack: Use struct_group() to zero struct nf_conn

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@...omium.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