[PATCH -next] media: dvb-usb: az6027: fix null-ptr-deref in az6027_i2c_xfer()

[Baisong Zhong]

Wei Chen reports a kernel bug as blew:

general protection fault, probably for non-canonical address
KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]
...
Call Trace:
<TASK>
__i2c_transfer+0x77e/0x1930 drivers/i2c/i2c-core-base.c:2109
i2c_transfer+0x1d5/0x3d0 drivers/i2c/i2c-core-base.c:2170
i2cdev_ioctl_rdwr+0x393/0x660 drivers/i2c/i2c-dev.c:297
i2cdev_ioctl+0x75d/0x9f0 drivers/i2c/i2c-dev.c:458
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]
__se_sys_ioctl+0xfb/0x170 fs/ioctl.c:856
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7fd834a8bded

In az6027_i2c_xfer(), if msg[i].addr is 0x99,
a null-ptr-deref will caused when accessing msg[i].buf.
For msg[i].len is 0 and msg[i].buf is null.

Fix this by checking msg[i].len in az6027_i2c_xfer().

Fixes: 76f9a820c867 ("V4L/DVB: AZ6027: Initial import of the driver")
Link: https://lore.kernel.org/lkml/CAO4mrfcPHB5aQJO=mpqV+p8mPLNg-Fok0gw8gZ=zemAfMGTzMg@xxxxxxxxxxxxxx/
Reported-by: Wei Chen <harperchen1110@xxxxxxxxx>
Signed-off-by: Baisong Zhong <zhongbaisong@xxxxxxxxxx>
---
 drivers/media/usb/dvb-usb/az6027.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/media/usb/dvb-usb/az6027.c b/drivers/media/usb/dvb-usb/az6027.c
index cf15988dfb51..7d78ee09be5e 100644
--- a/drivers/media/usb/dvb-usb/az6027.c
+++ b/drivers/media/usb/dvb-usb/az6027.c
@@ -975,6 +975,10 @@ static int az6027_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msg[], int n
 		if (msg[i].addr == 0x99) {
 			req = 0xBE;
 			index = 0;
+			if (msg[i].len < 1) {
+				i = -EOPNOTSUPP;
+				break;
+			}
 			value = msg[i].buf[0] & 0x00ff;
 			length = 1;
 			az6027_usb_out_op(d, req, value, index, data, length);
-- 
2.25.1