linux-kernel - RE: [PATCH][next] drivers: ipmi: fix off-by-one bounds check that leads to a out-of-bounds write

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Message-ID: <DB6PR0501MB2712BEBCF959566EAB063769DA340@DB6PR0501MB2712.eurprd05.prod.outlook.com>
Date:   Tue, 14 Jan 2020 15:50:22 +0000
From:   Asmaa Mnebhi <Asmaa@...lanox.com>
To:     Colin King <colin.king@...onical.com>,
        Corey Minyard <cminyard@...sta.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Vadim Pasternak <vadimp@...lanox.com>,
        "openipmi-developer@...ts.sourceforge.net" 
        <openipmi-developer@...ts.sourceforge.net>
CC:     "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH][next] drivers: ipmi: fix off-by-one bounds check that
 leads to a out-of-bounds write

Reviewed-by: Asmaa Mnebhi <asmaa@...lanox.com>

-----Original Message-----
From: Colin King <colin.king@...onical.com> 
Sent: Tuesday, January 14, 2020 9:41 AM
To: Corey Minyard <cminyard@...sta.com>; Arnd Bergmann <arnd@...db.de>; Greg Kroah-Hartman <gregkh@...uxfoundation.org>; Vadim Pasternak <vadimp@...lanox.com>; Asmaa Mnebhi <Asmaa@...lanox.com>; openipmi-developer@...ts.sourceforge.net
Cc: kernel-janitors@...r.kernel.org; linux-kernel@...r.kernel.org
Subject: [PATCH][next] drivers: ipmi: fix off-by-one bounds check that leads to a out-of-bounds write

From: Colin Ian King <colin.king@...onical.com>

The end of buffer check is off-by-one since the check is against an index that is pre-incremented before a store to buf[]. Fix this adjusting the bounds check appropriately.

Addresses-Coverity: ("Out-of-bounds write")
Fixes: 51bd6f291583 ("Add support for IPMB driver")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 drivers/char/ipmi/ipmb_dev_int.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/char/ipmi/ipmb_dev_int.c b/drivers/char/ipmi/ipmb_dev_int.c
index 9fdae83e59e0..382b28f1cf2f 100644
--- a/drivers/char/ipmi/ipmb_dev_int.c
+++ b/drivers/char/ipmi/ipmb_dev_int.c
@@ -279,7 +279,7 @@ static int ipmb_slave_cb(struct i2c_client *client,
 		break;
 
 	case I2C_SLAVE_WRITE_RECEIVED:
-		if (ipmb_dev->msg_idx >= sizeof(struct ipmb_msg))
+		if (ipmb_dev->msg_idx >= sizeof(struct ipmb_msg) - 1)
 			break;
 
 		buf[++ipmb_dev->msg_idx] = *val;
--
2.24.0