linux-hardening - Re: [PATCH v2][next] Bluetooth: hci_conn, hci_sync: Use __counted_by() in multiple structs and avoid -Wfamnae warnings

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Date: Mon, 29 Apr 2024 13:50:46 -0600
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Kees Cook <keescook@...omium.org>,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: Marcel Holtmann <marcel@...tmann.org>,
 Johan Hedberg <johan.hedberg@...il.com>,
 Luiz Augusto von Dentz <luiz.dentz@...il.com>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 linux-bluetooth@...r.kernel.org, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2][next] Bluetooth: hci_conn, hci_sync: Use
 __counted_by() in multiple structs and avoid -Wfamnae warnings

>> diff --git a/include/net/bluetooth/hci.h b/include/net/bluetooth/hci.h
>> index fe23e862921d..c4c6b8810701 100644
>> --- a/include/net/bluetooth/hci.h
>> +++ b/include/net/bluetooth/hci.h
>> @@ -2026,7 +2026,7 @@ struct hci_cp_le_set_ext_adv_data {
>>   	__u8  operation;
>>   	__u8  frag_pref;
>>   	__u8  length;
>> -	__u8  data[];
>> +	__u8  data[] __counted_by(length);
>>   } __packed;
> 
> I noticed some of the other structs here aren't flexible arrays, so it
> made me go take a look at these ones. I see that the only user of struct
> hci_cp_le_set_ext_adv_data uses a fixed-size array:
> 
>          struct {
>                  struct hci_cp_le_set_ext_adv_data cp;
>                  u8 data[HCI_MAX_EXT_AD_LENGTH];
>          } pdu;
> 
> Let's just change this from a flex array to a fixed-size array?

mmh... not sure about this. It would basically mean reverting this commit:

c9ed0a707730 ("Bluetooth: Fix Set Extended (Scan Response) Data")

--
Gustavo