linux-kernel - Re: [PATCH] Bluetooth: mark bacmp() and bacpy() as __always

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Date:   Mon, 09 Oct 2023 22:08:01 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Kees Cook" <keescook@...omium.org>
Cc:     "Arnd Bergmann" <arnd@...nel.org>,
        "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>, "Chun-Yi Lee" <jlee@...e.com>,
        "Luiz Augusto von Dentz" <luiz.von.dentz@...el.com>,
        stable@...r.kernel.org,
        "Iulia Tanasescu" <iulia.tanasescu@....com>,
        "Wenjia Zhang" <wenjia@...ux.ibm.com>,
        linux-bluetooth@...r.kernel.org, Netdev <netdev@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Bluetooth: mark bacmp() and bacpy() as __always_inline

On Mon, Oct 9, 2023, at 21:48, Kees Cook wrote:
> On Mon, Oct 09, 2023 at 08:23:08PM +0200, Arnd Bergmann wrote:
>> On Mon, Oct 9, 2023, at 18:02, Kees Cook wrote:
>> > On Mon, Oct 09, 2023 at 05:36:55PM +0200, Arnd Bergmann wrote:
>> >> On Mon, Oct 9, 2023, at 15:48, Arnd Bergmann wrote:
>> >> 
>> >> Sorry, I have to retract this, something went wrong on my
>> >> testing and I now see the same problem in some configs regardless
>> >> of whether the patch is applied or not.
>> >
>> > Perhaps turn them into macros instead?
>> 
>> I just tried that and still see the problem even with the macro,
>> so whatever gcc is doing must be a different issue. Maybe it
>> has correctly found a codepath that triggers this?
>> 
>> If you are able to help debug the issue better,
>> see these defconfigs for examples:
>> 
>> https://pastebin.com/raw/pC8Lnrn2
>> https://pastebin.com/raw/yb965unC
>
> This seems like a GCC bug. It is complaining about &hdev->bdaddr for
> some reason. This silences it:
>
> -	if (!bacmp(&hdev->bdaddr, &ev->bdaddr)) {
> +	a = hdev->bdaddr;
> +	if (!bacmp(&a, &ev->bdaddr)) {

Right, I see this addresses all instances. I tried another thing
and this also seems to address them for me:

--- a/net/bluetooth/hci_event.c
+++ b/net/bluetooth/hci_event.c
@@ -3273,7 +3273,7 @@ static void hci_conn_request_evt(struct hci_dev *hdev, void *data,
        /* Reject incoming connection from device with same BD ADDR against
         * CVE-2020-26555
         */
-       if (!bacmp(&hdev->bdaddr, &ev->bdaddr)) {
+       if (hdev && !bacmp(&hdev->bdaddr, &ev->bdaddr)) {
                bt_dev_dbg(hdev, "Reject connection with same BD_ADDR %pMR\n",
                           &ev->bdaddr);
                hci_reject_conn(hdev, &ev->bdaddr);

and also this one does the trick:

--- a/include/net/bluetooth/bluetooth.h
+++ b/include/net/bluetooth/bluetooth.h
@@ -266,7 +266,7 @@ void bt_err_ratelimited(const char *fmt, ...);
 #define BT_DBG(fmt, ...)       pr_debug(fmt "\n", ##__VA_ARGS__)
 #endif
 
-#define bt_dev_name(hdev) ((hdev) ? (hdev)->name : "null")
+#define bt_dev_name(hdev) ((hdev)->name)
 
 #define bt_dev_info(hdev, fmt, ...)                            \
        BT_INFO("%s: " fmt, bt_dev_name(hdev), ##__VA_ARGS__)

So what is actually going on is that the bt_dev_dbg() introduces
the idea that hdev might be NULL because of the check.

     Arnd