linux-hardening - [PATCH] Bluetooth: mgmt: Pessimize compile-time bounds-check

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Date:   Tue, 17 Aug 2021 21:39:12 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Marcel Holtmann <marcel@...tmann.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        linux-bluetooth@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH] Bluetooth: mgmt: Pessimize compile-time bounds-check

After gaining __alloc_size hints, GCC thinks it can reach a memcpy()
with eir_len == 0 (since it can't see into the rewrite of status).
Instead, check eir_len == 0, avoiding this future warning:

In function 'eir_append_data',
    inlined from 'read_local_oob_ext_data_complete' at net/bluetooth/mgmt.c:7210:12:
./include/linux/fortify-string.h:54:29: warning: '__builtin_memcpy' offset 5 is out of the bounds [0, 3] [-Warray-bounds]
...
net/bluetooth/hci_request.h:133:2: note: in expansion of macro 'memcpy'
  133 |  memcpy(&eir[eir_len], data, data_len);
      |  ^~~~~~

Cc: Marcel Holtmann <marcel@...tmann.org>
Cc: Johan Hedberg <johan.hedberg@...il.com>
Cc: Luiz Augusto von Dentz <luiz.dentz@...il.com>
Cc: "David S. Miller" <davem@...emloft.net>
Cc: Jakub Kicinski <kuba@...nel.org>
Cc: linux-bluetooth@...r.kernel.org
Cc: netdev@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 net/bluetooth/mgmt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/bluetooth/mgmt.c b/net/bluetooth/mgmt.c
index 1e21e014efd2..cea01e275f1e 100644
--- a/net/bluetooth/mgmt.c
+++ b/net/bluetooth/mgmt.c
@@ -7204,7 +7204,7 @@ static void read_local_oob_ext_data_complete(struct hci_dev *hdev, u8 status,
 	if (!mgmt_rp)
 		goto done;
 
-	if (status)
+	if (eir_len == 0)
 		goto send_rsp;
 
 	eir_len = eir_append_data(mgmt_rp->eir, 0, EIR_CLASS_OF_DEV,
-- 
2.30.2