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From: Arnd Bergmann <arnd@kernel.org>
To: Marcel Holtmann <marcel@holtmann.org>,
	Johan Hedberg <johan.hedberg@gmail.com>,
	Luiz Augusto von Dentz <luiz.dentz@gmail.com>,
	"Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>,
	Iulia Tanasescu <iulia.tanasescu@nxp.com>,
	Pauli Virtanen <pav@iki.fi>,
	Jakub Kicinski <kuba@kernel.org>,
	"Lee, Chun-Yi" <jlee@suse.com>,
	Claudia Draghicescu <claudia.rosu@nxp.com>,
	Ziyang Xuan <william.xuanziyang@huawei.com>,
	linux-bluetooth@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH] Bluetooth: hci_event: shut up a false-positive warning
Date: Wed, 22 Nov 2023 23:17:44 +0100
Message-Id: <20231122221805.3139482-1-arnd@kernel.org>
Precedence: bulk
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From: Arnd Bergmann <arnd@arndb.de>

Turning on -Wstringop-overflow globally exposed a misleading compiler
warning in bluetooth:

net/bluetooth/hci_event.c: In function 'hci_cc_read_class_of_dev':
net/bluetooth/hci_event.c:524:9: error: 'memcpy' writing 3 bytes into a region of size 0 overflows the destination [-Werror=stringop-overflow=]
  524 |         memcpy(hdev->dev_class, rp->dev_class, 3);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The problem here is the check for hdev being NULL in bt_dev_dbg() that
leads the compiler to conclude that hdev->dev_class might be an invalid
pointer access.

Add another explicit check for the same condition to make sure gcc sees
this cannot happen.

Fixes: a9de9248064b ("[Bluetooth] Switch from OGF+OCF to using only opcodes")
Fixes: 1b56c90018f0 ("Makefile: Enable -Wstringop-overflow globally")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 net/bluetooth/hci_event.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
index 5b6fd625fc09..5651e96e78da 100644
--- a/net/bluetooth/hci_event.c
+++ b/net/bluetooth/hci_event.c
@@ -516,6 +516,9 @@ static u8 hci_cc_read_class_of_dev(struct hci_dev *hdev, void *data,
 {
 	struct hci_rp_read_class_of_dev *rp = data;
 
+	if (WARN_ON(!hdev))
+		return -ENXIO;
+
 	bt_dev_dbg(hdev, "status 0x%2.2x", rp->status);
 
 	if (rp->status)
-- 
2.39.2