[PATCH 1/7] wifi: cfg80211: Annotate struct cfg80211_acl_data with __counted_by

From: Kees Cook
Date: Thu Aug 17 2023 - 17:16:22 EST


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@xxxxxxxxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
Cc: Paolo Abeni <pabeni@xxxxxxxxxx>
Cc: linux-wireless@xxxxxxxxxxxxxxx
Cc: netdev@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
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