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

[Kees Cook]

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@xxxxxxxxxxxx>
Cc: Johan Hedberg <johan.hedberg@xxxxxxxxx>
Cc: Luiz Augusto von Dentz <luiz.dentz@xxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
Cc: linux-bluetooth@xxxxxxxxxxxxxxx
Cc: netdev@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 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