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@sipsolutions.net>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: linux-wireless@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 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

On 8/17/2023 2:15 PM, 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_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@sipsolutions.net>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Eric Dumazet <edumazet@google.com>
> Cc: Jakub Kicinski <kuba@kernel.org>
> Cc: Paolo Abeni <pabeni@redhat.com>
> Cc: linux-wireless@vger.kernel.org
> Cc: netdev@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>

Reviewed-by: Jeff Johnson <quic_jjohnson@quicinc.com>

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_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@sipsolutions.net>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Eric Dumazet <edumazet@google.com>
> Cc: Jakub Kicinski <kuba@kernel.org>
> Cc: Paolo Abeni <pabeni@redhat.com>
> Cc: linux-wireless@vger.kernel.org
> Cc: netdev@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>

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

Thanks
--
Gustavo

> ---
>   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;
>