syzbot reported a uninit-value in cxusb_i2c_xfer. [1]

Only when the write operation of usb_bulk_msg() in dvb_usb_generic_rw()
succeeds and rlen is greater than 0, the read operation of usb_bulk_msg()
will be executed to read rlen bytes of data from the dvb device into the
rbuf.

In this case, although rlen is 1, the write operation failed which resulted
in the dvb read operation not being executed, and ultimately variable i was
not initialized.

[1]
BUG: KMSAN: uninit-value in cxusb_gpio_tuner drivers/media/usb/dvb-usb/cxusb.c:124 [inline]
BUG: KMSAN: uninit-value in cxusb_i2c_xfer+0x153a/0x1a60 drivers/media/usb/dvb-usb/cxusb.c:196
 cxusb_gpio_tuner drivers/media/usb/dvb-usb/cxusb.c:124 [inline]
 cxusb_i2c_xfer+0x153a/0x1a60 drivers/media/usb/dvb-usb/cxusb.c:196
 __i2c_transfer+0xe25/0x3150 drivers/i2c/i2c-core-base.c:-1
 i2c_transfer+0x317/0x4a0 drivers/i2c/i2c-core-base.c:2315
 i2c_transfer_buffer_flags+0x125/0x1e0 drivers/i2c/i2c-core-base.c:2343
 i2c_master_send include/linux/i2c.h:109 [inline]
 i2cdev_write+0x210/0x280 drivers/i2c/i2c-dev.c:183
 do_loop_readv_writev fs/read_write.c:848 [inline]
 vfs_writev+0x963/0x14e0 fs/read_write.c:1057
 do_writev+0x247/0x5c0 fs/read_write.c:1101
 __do_sys_writev fs/read_write.c:1169 [inline]
 __se_sys_writev fs/read_write.c:1166 [inline]
 __x64_sys_writev+0x98/0xe0 fs/read_write.c:1166
 x64_sys_call+0x2229/0x3c80 arch/x86/include/generated/asm/syscalls_64.h:21
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x1e0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported-by: syzbot+526bd95c0ec629993bf3@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=526bd95c0ec629993bf3
Tested-by: syzbot+526bd95c0ec629993bf3@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
 drivers/media/usb/dvb-usb/cxusb.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/media/usb/dvb-usb/cxusb.c b/drivers/media/usb/dvb-usb/cxusb.c
index f44529b40989..d0501c1e81d6 100644
--- a/drivers/media/usb/dvb-usb/cxusb.c
+++ b/drivers/media/usb/dvb-usb/cxusb.c
@@ -119,9 +119,8 @@ static void cxusb_gpio_tuner(struct dvb_usb_device *d, int onoff)
 
 	o[0] = GPIO_TUNER;
 	o[1] = onoff;
-	cxusb_ctrl_msg(d, CMD_GPIO_WRITE, o, 2, &i, 1);
 
-	if (i != 0x01)
+	if (!cxusb_ctrl_msg(d, CMD_GPIO_WRITE, o, 2, &i, 1) && i != 0x01)
 		dev_info(&d->udev->dev, "gpio_write failed.\n");
 
 	st->gpio_write_state[GPIO_TUNER] = onoff;
-- 
2.43.0