linux-hardening - Re: [PATCH 3/7] wifi: cfg80211: Annotate struct cfg80211_mbssid_elems with __counted

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Message-ID: <343b8571-28e4-665c-7652-15920d91cb4d@embeddedor.com>
Date:   Thu, 17 Aug 2023 15:24:04 -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 3/7] wifi: cfg80211: Annotate struct cfg80211_mbssid_elems
 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_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@...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 | 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;
>   }
>