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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, rkardell@mida.se,
        Mauro Carvalho Chehab <mchehab+huawei@kernel.org>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.16 0621/1039] media: m920x: dont use stack on USB reads
Date:   Mon, 24 Jan 2022 19:40:10 +0100
Message-Id: <20220124184146.213169199@linuxfoundation.org>
In-Reply-To: <20220124184125.121143506@linuxfoundation.org>
References: <20220124184125.121143506@linuxfoundation.org>
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From: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

[ Upstream commit a2ab06d7c4d6bfd0b545a768247a70463e977e27 ]

Using stack-allocated pointers for USB message data don't work.
This driver is almost OK with that, except for the I2C read
logic.

Fix it by using a temporary read buffer, just like on all other
calls to m920x_read().

Link: https://lore.kernel.org/all/ccc99e48-de4f-045e-0fe4-61e3118e3f74@mida.se/
Reported-by: rkardell@mida.se
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/media/usb/dvb-usb/m920x.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/media/usb/dvb-usb/m920x.c b/drivers/media/usb/dvb-usb/m920x.c
index 4bb5b82599a79..691e05833db19 100644
--- a/drivers/media/usb/dvb-usb/m920x.c
+++ b/drivers/media/usb/dvb-usb/m920x.c
@@ -274,6 +274,13 @@ static int m920x_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msg[], int nu
 			/* Should check for ack here, if we knew how. */
 		}
 		if (msg[i].flags & I2C_M_RD) {
+			char *read = kmalloc(1, GFP_KERNEL);
+			if (!read) {
+				ret = -ENOMEM;
+				kfree(read);
+				goto unlock;
+			}
+
 			for (j = 0; j < msg[i].len; j++) {
 				/* Last byte of transaction?
 				 * Send STOP, otherwise send ACK. */
@@ -281,9 +288,12 @@ static int m920x_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msg[], int nu
 
 				if ((ret = m920x_read(d->udev, M9206_I2C, 0x0,
 						      0x20 | stop,
-						      &msg[i].buf[j], 1)) != 0)
+						      read, 1)) != 0)
 					goto unlock;
+				msg[i].buf[j] = read[0];
 			}
+
+			kfree(read);
 		} else {
 			for (j = 0; j < msg[i].len; j++) {
 				/* Last byte of transaction? Then send STOP. */
-- 
2.34.1