linux-hardening - [PATCH 3/7] wifi: cfg80211: Annotate struct cfg80211_mbssid_elems with __counted

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Date:   Thu, 17 Aug 2023 14:15:25 -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 3/7] wifi: cfg80211: Annotate struct cfg80211_mbssid_elems 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_mbssid_elems.
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 | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/net/cfg80211.h b/include/net/cfg80211.h
index eb73b5af5d04..5c7d091b3925 100644
--- a/include/net/cfg80211.h
+++ b/include/net/cfg80211.h
@@ -1187,7 +1187,7 @@ struct cfg80211_mbssid_elems {
 	struct {
 		const u8 *data;
 		size_t len;
-	} elem[];
+	} elem[] __counted_by(cnt);
 };
 
 /**
diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index 80633e815311..9ba4266368db 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -5438,13 +5438,13 @@ nl80211_parse_mbssid_elems(struct wiphy *wiphy, struct nlattr *attrs)
 	elems = kzalloc(struct_size(elems, elem, num_elems), GFP_KERNEL);
 	if (!elems)
 		return ERR_PTR(-ENOMEM);
+	elems->cnt = num_elems;
 
 	nla_for_each_nested(nl_elems, attrs, rem_elems) {
 		elems->elem[i].data = nla_data(nl_elems);
 		elems->elem[i].len = nla_len(nl_elems);
 		i++;
 	}
-	elems->cnt = num_elems;
 	return elems;
 }
 
-- 
2.34.1