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* [PATCH] Bluetooth: mgmt: Pessimize compile-time bounds-check
@ 2021-08-18  4:39 Kees Cook
  2021-08-19 14:52 ` Marcel Holtmann
  0 siblings, 1 reply; 2+ messages in thread
From: Kees Cook @ 2021-08-18  4:39 UTC (permalink / raw)
  To: Marcel Holtmann
  Cc: Kees Cook, Johan Hedberg, Luiz Augusto von Dentz,
	David S. Miller, Jakub Kicinski, linux-bluetooth, netdev,
	linux-kernel, linux-hardening

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@holtmann.org>
Cc: Johan Hedberg <johan.hedberg@gmail.com>
Cc: Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: linux-bluetooth@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.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


^ permalink raw reply	[flat|nested] 2+ messages in thread

* Re: [PATCH] Bluetooth: mgmt: Pessimize compile-time bounds-check
  2021-08-18  4:39 [PATCH] Bluetooth: mgmt: Pessimize compile-time bounds-check Kees Cook
@ 2021-08-19 14:52 ` Marcel Holtmann
  0 siblings, 0 replies; 2+ messages in thread
From: Marcel Holtmann @ 2021-08-19 14:52 UTC (permalink / raw)
  To: Kees Cook
  Cc: Johan Hedberg, Luiz Augusto von Dentz, David S. Miller,
	Jakub Kicinski, open list:BLUETOOTH SUBSYSTEM,
	open list:NETWORKING [GENERAL],
	open list, linux-hardening

Hi Kees,

> 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@holtmann.org>
> Cc: Johan Hedberg <johan.hedberg@gmail.com>
> Cc: Luiz Augusto von Dentz <luiz.dentz@gmail.com>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Jakub Kicinski <kuba@kernel.org>
> Cc: linux-bluetooth@vger.kernel.org
> Cc: netdev@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> net/bluetooth/mgmt.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)

patch has been applied to bluetooth-next tree.

Regards

Marcel


^ permalink raw reply	[flat|nested] 2+ messages in thread

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