[PATCH 5.15 043/110] media: dvb-usb-v2: af9035: Fix null-ptr-deref in af9035_i2c_master_xfer

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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

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

From: Zhang Shurong <zhang_shurong@foxmail.com>

[ Upstream commit 7bf744f2de0a848fb1d717f5831b03db96feae89 ]

In af9035_i2c_master_xfer, msg is controlled by user. When msg[i].buf
is null and msg[i].len is zero, former checks on msg[i].buf would be
passed. Malicious data finally reach af9035_i2c_master_xfer. If accessing
msg[i].buf[0] without sanity check, null ptr deref would happen.
We add check on msg[i].len to prevent crash.

Similar commit:
commit 0ed554fd769a
("media: dvb-usb: az6027: fix null-ptr-deref in az6027_i2c_xfer()")

Signed-off-by: Zhang Shurong <zhang_shurong@foxmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Sasha Levin <sashal@kernel.org>
[ moved variable declaration to fix build issues in older kernels - gregkh ]
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/media/usb/dvb-usb-v2/af9035.c |   14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

--- a/drivers/media/usb/dvb-usb-v2/af9035.c
+++ b/drivers/media/usb/dvb-usb-v2/af9035.c
@@ -270,6 +270,7 @@ static int af9035_i2c_master_xfer(struct
 	struct dvb_usb_device *d = i2c_get_adapdata(adap);
 	struct state *state = d_to_priv(d);
 	int ret;
+	u32 reg;
 
 	if (mutex_lock_interruptible(&d->i2c_mutex) < 0)
 		return -EAGAIN;
@@ -322,8 +323,10 @@ static int af9035_i2c_master_xfer(struct
 			ret = -EOPNOTSUPP;
 		} else if ((msg[0].addr == state->af9033_i2c_addr[0]) ||
 			   (msg[0].addr == state->af9033_i2c_addr[1])) {
+			if (msg[0].len < 3 || msg[1].len < 1)
+				return -EOPNOTSUPP;
 			/* demod access via firmware interface */
-			u32 reg = msg[0].buf[0] << 16 | msg[0].buf[1] << 8 |
+			reg = msg[0].buf[0] << 16 | msg[0].buf[1] << 8 |
 					msg[0].buf[2];
 
 			if (msg[0].addr == state->af9033_i2c_addr[1])
@@ -381,17 +384,16 @@ static int af9035_i2c_master_xfer(struct
 			ret = -EOPNOTSUPP;
 		} else if ((msg[0].addr == state->af9033_i2c_addr[0]) ||
 			   (msg[0].addr == state->af9033_i2c_addr[1])) {
+			if (msg[0].len < 3)
+				return -EOPNOTSUPP;
 			/* demod access via firmware interface */
-			u32 reg = msg[0].buf[0] << 16 | msg[0].buf[1] << 8 |
+			reg = msg[0].buf[0] << 16 | msg[0].buf[1] << 8 |
 					msg[0].buf[2];
 
 			if (msg[0].addr == state->af9033_i2c_addr[1])
 				reg |= 0x100000;
 
-			ret = (msg[0].len >= 3) ? af9035_wr_regs(d, reg,
-							         &msg[0].buf[3],
-							         msg[0].len - 3)
-					        : -EOPNOTSUPP;
+			ret = af9035_wr_regs(d, reg, &msg[0].buf[3], msg[0].len - 3);
 		} else {
 			/* I2C write */
 			u8 buf[MAX_XFER_SIZE];