[PATCH] iio: backend: fix uninitialized data in debugfs

[Dan Carpenter <error27@gmail.com>]

If the *ppos value is non-zero then simple_write_to_buffer() will not
initialize the start of the buf[] buffer.  Non-zero ppos values aren't
going to work at all.  Check for that at the start of the function and
return -EINVAL.

Fixes: cdf01e0809a4 ("iio: backend: add debugFs interface")
Signed-off-by: Dan Carpenter <error27@gmail.com>
---
 drivers/iio/industrialio-backend.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iio/industrialio-backend.c b/drivers/iio/industrialio-backend.c
index 138ebebc9c0d..4763e224ebc6 100644
--- a/drivers/iio/industrialio-backend.c
+++ b/drivers/iio/industrialio-backend.c
@@ -156,7 +156,7 @@ static ssize_t iio_backend_debugfs_write_reg(struct file *file,
 	ssize_t rc;
 	int ret;
 
-	if (count >= sizeof(buf))
+	if (*ppos != 0 || count >= sizeof(buf))
 		return -ENOSPC;
 
 	rc = simple_write_to_buffer(buf, sizeof(buf) - 1, ppos, userbuf, count);
-- 
2.53.0