Re: [PATCH 12/32] cfg80211: Use mem_to_flex_dup() with struct cfg80211_bss_ies

[Johannes Berg <johannes@xxxxxxxxxxxxxxxx>]

On Tue, 2022-05-03 at 18:44 -0700, Kees Cook wrote:
> 
> @@ -2277,7 +2274,7 @@ cfg80211_update_notlisted_nontrans(struct wiphy *wiphy,
>       size_t ielen = len - offsetof(struct ieee80211_mgmt,
>                                     u.probe_resp.variable);
>       size_t new_ie_len;
> -     struct cfg80211_bss_ies *new_ies;
> +     struct cfg80211_bss_ies *new_ies = NULL;
>       const struct cfg80211_bss_ies *old;
>       u8 cpy_len;
>  
> @@ -2314,8 +2311,7 @@ cfg80211_update_notlisted_nontrans(struct wiphy *wiphy,
>       if (!new_ie)
>               return;
>  
> -     new_ies = kzalloc(sizeof(*new_ies) + new_ie_len, GFP_ATOMIC);
> -     if (!new_ies)
> +     if (mem_to_flex_dup(&new_ies, new_ie, new_ie_len, GFP_ATOMIC))
>               goto out_free;
>  
>       pos = new_ie;
> @@ -2333,10 +2329,8 @@ cfg80211_update_notlisted_nontrans(struct wiphy *wiphy,
>       memcpy(pos, mbssid + cpy_len, ((ie + ielen) - (mbssid + cpy_len)));
>  
>       /* update ie */
> -     new_ies->len = new_ie_len;
>       new_ies->tsf = le64_to_cpu(mgmt->u.probe_resp.timestamp);
>       new_ies->from_beacon = ieee80211_is_beacon(mgmt->frame_control);
> -     memcpy(new_ies->data, new_ie, new_ie_len);

This introduces a bug, "new_ie" is modified between the kzalloc() and
the memcpy(), but you've moved the memcpy() into the allocation. In
fact, new_ie is completely freshly kzalloc()'ed at this point. So you
need to change the ordering here, but since new_ie is freed pretty much
immediately, we can probably just build the stuff directly inside
new_ies->data, though then of course we cannot use your helper anymore?

johannes