netdev - [PATCH 1/7] wifi: cfg80211: Annotate struct cfg80211_acl_data with __counted

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Date: Thu, 17 Aug 2023 14:15:23 -0700
From: Kees Cook <keescook@...omium.org>
To: Johannes Berg <johannes@...solutions.net>
Cc: Kees Cook <keescook@...omium.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	linux-wireless@...r.kernel.org,
	netdev@...r.kernel.org,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Tom Rix <trix@...hat.com>,
	linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev,
	linux-hardening@...r.kernel.org
Subject: [PATCH 1/7] wifi: cfg80211: Annotate struct cfg80211_acl_data with __counted_by

Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
(for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

As found with Coccinelle[1], add __counted_by for struct cfg80211_acl_data.
Additionally, since the element count member must be set before accessing
the annotated flexible array member, move its initialization earlier.

[1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci

Cc: Johannes Berg <johannes@...solutions.net>
Cc: "David S. Miller" <davem@...emloft.net>
Cc: Eric Dumazet <edumazet@...gle.com>
Cc: Jakub Kicinski <kuba@...nel.org>
Cc: Paolo Abeni <pabeni@...hat.com>
Cc: linux-wireless@...r.kernel.org
Cc: netdev@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 include/net/cfg80211.h | 2 +-
 net/wireless/nl80211.c | 3 +--
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/include/net/cfg80211.h b/include/net/cfg80211.h
index d6fa7c8767ad..eb73b5af5d04 100644
--- a/include/net/cfg80211.h
+++ b/include/net/cfg80211.h
@@ -1282,7 +1282,7 @@ struct cfg80211_acl_data {
 	int n_acl_entries;
 
 	/* Keep it last */
-	struct mac_address mac_addrs[];
+	struct mac_address mac_addrs[] __counted_by(n_acl_entries);
 };
 
 /**
diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index 8bcf8e293308..80633e815311 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -4889,13 +4889,12 @@ static struct cfg80211_acl_data *parse_acl_data(struct wiphy *wiphy,
 	acl = kzalloc(struct_size(acl, mac_addrs, n_entries), GFP_KERNEL);
 	if (!acl)
 		return ERR_PTR(-ENOMEM);
+	acl->n_acl_entries = n_entries;
 
 	nla_for_each_nested(attr, info->attrs[NL80211_ATTR_MAC_ADDRS], tmp) {
 		memcpy(acl->mac_addrs[i].addr, nla_data(attr), ETH_ALEN);
 		i++;
 	}
-
-	acl->n_acl_entries = n_entries;
 	acl->acl_policy = acl_policy;
 
 	return acl;
-- 
2.34.1