[PATCH 4/7] wifi: cfg80211: Annotate struct cfg80211_pmsr_request with __counted_by

[Kees Cook]

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_pmsr_request.
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/pmsr.c    | 3 +--
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/include/net/cfg80211.h b/include/net/cfg80211.h
index 5c7d091b3925..e9ca4726a732 100644
--- a/include/net/cfg80211.h
+++ b/include/net/cfg80211.h
@@ -3948,7 +3948,7 @@ struct cfg80211_pmsr_request {
 
 	struct list_head list;
 
-	struct cfg80211_pmsr_request_peer peers[];
+	struct cfg80211_pmsr_request_peer peers[] __counted_by(n_peers);
 };
 
 /**
diff --git a/net/wireless/pmsr.c b/net/wireless/pmsr.c
index 77000a264855..9611aa0bd051 100644
--- a/net/wireless/pmsr.c
+++ b/net/wireless/pmsr.c
@@ -291,6 +291,7 @@ int nl80211_pmsr_start(struct sk_buff *skb, struct genl_info *info)
 	req = kzalloc(struct_size(req, peers, count), GFP_KERNEL);
 	if (!req)
 		return -ENOMEM;
+	req->n_peers = count;
 
 	if (info->attrs[NL80211_ATTR_TIMEOUT])
 		req->timeout = nla_get_u32(info->attrs[NL80211_ATTR_TIMEOUT]);
@@ -321,8 +322,6 @@ int nl80211_pmsr_start(struct sk_buff *skb, struct genl_info *info)
 			goto out_err;
 		idx++;
 	}
-
-	req->n_peers = count;
 	req->cookie = cfg80211_assign_cookie(rdev);
 	req->nl_portid = info->snd_portid;
 
-- 
2.34.1