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

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Message-ID: <CAFhGd8ra6vpUvLc_Z7zRA8kVOzu7=o6b6vFL+QvcGi34-nVmFg@mail.gmail.com>
Date:   Thu, 17 Aug 2023 14:21:10 -0700
From:   Justin Stitt <justinstitt@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Johannes Berg <johannes@...solutions.net>,
        "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 Thu, Aug 17, 2023 at 2:16 PM Kees Cook <keescook@...omium.org> 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: Justin Stitt <justinstitt@...gle.com>

> ---
>  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
>