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

[Asmaa Mnebhi]

Reviewed-by: Asmaa Mnebhi <asmaa@xxxxxxxxxxxx>

-----Original Message-----
From: Colin King <colin.king@xxxxxxxxxxxxx> 
Sent: Tuesday, January 14, 2020 9:41 AM
To: Corey Minyard <cminyard@xxxxxxxxxx>; Arnd Bergmann <arnd@xxxxxxxx>; Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>; Vadim Pasternak <vadimp@xxxxxxxxxxxx>; Asmaa Mnebhi <Asmaa@xxxxxxxxxxxx>; openipmi-developer@xxxxxxxxxxxxxxxxxxxxx
Cc: kernel-janitors@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
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@xxxxxxxxxxxxx>

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@xxxxxxxxxxxxx>
---
 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