Subject: Re: [PATCH] 4.9.13 brcmfmac: fix use-after-free on resume
To: Daniel J Blueman <daniel@quora.org>
References: <CAMVG2stHA9qSUiRFBW=-4jhSMk-o7Frext+Qf9JK3Fo822XHhw@mail.gmail.com>
 <3626494c-8482-d003-1c83-e6171f6990a8@broadcom.com>
 <CAMVG2st=ZW-HhqQOMnDunjSJHj8Zw_K2+w2_8AVsHQePN3Ow9w@mail.gmail.com>
Cc: Hante Meuleman <hante.meuleman@broadcom.com>,
        Pieter-Paul Giesberts <pieterpg@broadcom.com>,
        Netdev <netdev@vger.kernel.org>,
        David Miller <davem@davemloft.net>,
        linux-wireless <linux-wireless@vger.kernel.org>
From: Arend Van Spriel <arend.vanspriel@broadcom.com>
Message-ID: <1a978960-3962-0eda-15b0-b1259b21e58f@broadcom.com> (sfid-20170313_103348_171462_1874E5A5)
Date: Mon, 13 Mar 2017 10:33:27 +0100
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In-Reply-To: <CAMVG2st=ZW-HhqQOMnDunjSJHj8Zw_K2+w2_8AVsHQePN3Ow9w@mail.gmail.com>
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Sender: linux-wireless-owner@vger.kernel.org

On 6-3-2017 15:50, Daniel J Blueman wrote:
> On 6 March 2017 at 21:00, Arend Van Spriel <arend.vanspriel@broadcom.com> wrote:
>> + linux-wireless
>>
>> On 6-3-2017 8:14, Daniel J Blueman wrote:
>>> KASAN reported 'struct wireless_dev wdev' was read after being freed.
>>> Fix by freeing after the access.
>>
>> I would rather like to see the KASAN report, because something is off
>> here. This function is called with wdev as a parameter so how can it be
>> accessed after free here? brcmf_remove_interface() does not free the
>> wdev nor the brcmf_cfg80211_vif instance which contains the wdev.
>>
>> Regards,
>> Arend
>>
>>> Signed-off-by: Daniel J Blueman <daniel@quora.org>
>>>
>>> diff --git a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/p2p.c
>>> b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/p2p.c
>>> index de19c7c..aa0f470 100644
>>> --- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/p2p.c
>>> +++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/p2p.c
>>> @@ -2288,12 +2288,13 @@ int brcmf_p2p_del_vif(struct wiphy *wiphy,
>>> struct wireless_dev *wdev)
>>>                 else
>>>                         err = 0;
>>>         }
>>> -       brcmf_remove_interface(vif->ifp, true);
>>>
>>> -       brcmf_cfg80211_arm_vif_event(cfg, NULL);
>>>         if (vif->wdev.iftype != NL80211_IFTYPE_P2P_DEVICE)
>>>                 p2p->bss_idx[P2PAPI_BSSCFG_CONNECTION].vif = NULL;
>>>
>>> +       brcmf_remove_interface(vif->ifp, true);
>>> +       brcmf_cfg80211_arm_vif_event(cfg, NULL);
>>> +
>>>         return err;
>>>  }
> 
> Sure, https://quora.org/kernel/brcmfmac/dmesg.txt

So this dmesg looks to be about a separate issue during resume, which
you sent an email about earlier [1] which is about using wiphy struct
after free. However, back to this I further checked the code and it
seems the vif is indeed freed through the netdev destructor callback
upon calling brcmf_remove_inteface(). However, I would prefer to store
vif->wdev.iftype in a local variable and avoid changing the order of the
calls in the code.

Regards,
Arend

[1] http://marc.info/?l=linux-netdev&m=148878437808750&w=2

> vmlinux, cfg80211.o, brcmfmac.o and config are in the same path; this
> is against v4.9.13 stock.