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Re: [PATCH 3/7] wifi: cfg80211: Annotate struct cfg80211_mbssid_elems with __counted_by

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On 8/17/23 15:15, Kees Cook wrote:
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@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>

Reviewed-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>

Thanks
--
Gustavo

---
  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;
  }



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