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Date:   Wed, 4 May 2022 08:13:12 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     "Gustavo A . R . Silva" <gustavoars@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        alsa-devel@...a-project.org, Al Viro <viro@...iv.linux.org.uk>,
        Andrew Gabbasov <andrew_gabbasov@...tor.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Gross <agross@...nel.org>,
        Andy Lavr <andy.lavr@...il.com>,
        Arend van Spriel <aspriel@...il.com>,
        Baowen Zheng <baowen.zheng@...igine.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Bradley Grove <linuxdrivers@...otech.com>,
        brcm80211-dev-list.pdl@...adcom.com,
        Christian Brauner <brauner@...nel.org>,
        Christian Göttsche <cgzones@...glemail.com>,
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        Xiu Jianfeng <xiujianfeng@...wei.com>,
        Yang Yingliang <yangyingliang@...wei.com>
Subject: Re: [PATCH 12/32] cfg80211: Use mem_to_flex_dup() with struct
 cfg80211_bss_ies

On Wed, May 04, 2022 at 09:28:46AM +0200, Johannes Berg wrote:
> 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?

Eek, yes, thanks. My attempt to locate the alloc/memcpy pattern failed
to take into account anything touch the source between alloc and memcpy.
I'll double check the other examples.

-Kees

-- 
Kees Cook

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