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

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Message-ID: <202310091246.ED5A2AFB21@keescook>
Date:   Mon, 9 Oct 2023 12:48:15 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Arnd Bergmann <arnd@...db.de>
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 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:

diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
index 6f4409b4c364..509e86b36576 100644
--- a/net/bluetooth/hci_event.c
+++ b/net/bluetooth/hci_event.c
@@ -3266,6 +3266,7 @@ static void hci_conn_request_evt(struct hci_dev *hdev, void *data,
 	int mask = hdev->link_mode;
 	struct inquiry_entry *ie;
 	struct hci_conn *conn;
+	bdaddr_t a;
 	__u8 flags = 0;
 
 	bt_dev_dbg(hdev, "bdaddr %pMR type 0x%x", &ev->bdaddr, ev->link_type);
@@ -3273,7 +3274,8 @@ 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)) {
+	a = hdev->bdaddr;
+	if (!bacmp(&a, &ev->bdaddr)) {
 		bt_dev_dbg(hdev, "Reject connection with same BD_ADDR %pMR\n",
 			   &ev->bdaddr);
 		hci_reject_conn(hdev, &ev->bdaddr);

:(

-- 
Kees Cook