linux-kernel - [PATCH 3.10 32/43] Bluetooth: Fix HCI H5 corrupted ack value

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Message-Id: <20141028033524.777843874@linuxfoundation.org>
Date:	Tue, 28 Oct 2014 11:36:30 +0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Loic Poulain <loic.poulain@...el.com>,
	Marcel Holtmann <marcel@...tmann.org>
Subject: [PATCH 3.10 32/43] Bluetooth: Fix HCI H5 corrupted ack value

3.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Loic Poulain <loic.poulain@...el.com>

commit 4807b51895dce8aa650ebebc51fa4a795ed6b8b8 upstream.

In this expression: seq = (seq - 1) % 8
seq (u8) is implicitly converted to an int in the arithmetic operation.
So if seq value is 0, operation is ((0 - 1) % 8) => (-1 % 8) => -1.
The new seq value is 0xff which is an invalid ACK value, we expect 0x07.
It leads to frequent dropped ACK and retransmission.
Fix this by using '&' binary operator instead of '%'.

Signed-off-by: Loic Poulain <loic.poulain@...el.com>
Signed-off-by: Marcel Holtmann <marcel@...tmann.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/bluetooth/hci_h5.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/bluetooth/hci_h5.c
+++ b/drivers/bluetooth/hci_h5.c
@@ -237,7 +237,7 @@ static void h5_pkt_cull(struct h5 *h5)
 			break;
 
 		to_remove--;
-		seq = (seq - 1) % 8;
+		seq = (seq - 1) & 0x07;
 	}
 
 	if (seq != h5->rx_ack)


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