linux-hardening - Re: [PATCH 1/7] wifi: cfg80211: Annotate struct cfg80211_acl_data with __counted

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Date:   Thu, 17 Aug 2023 15:23:37 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Kees Cook <keescook@...omium.org>,
        Johannes Berg <johannes@...solutions.net>
Cc:     "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: Re: [PATCH 1/7] wifi: cfg80211: Annotate struct cfg80211_acl_data
 with __counted_by



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_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@...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>

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

Thanks
--
Gustavo

> ---
>   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;