[PATCH] drm: zynqmp_dp: Fix uninitialized variable in debugfs()

[Dan Carpenter <error27@gmail.com>]

If the *ppos is non-zero then simple_write_to_buffer() will not
initialize the start of the buf[] buffer.  It doesn't really make sense
to allow non-zero values for *ppos, so check for that at the start and
return -EINVAL.

Fixes: 28edaacb821c ("drm: zynqmp_dp: Add debugfs interface for compliance testing")
Signed-off-by: Dan Carpenter <error27@gmail.com>
---
 drivers/gpu/drm/xlnx/zynqmp_dp.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/xlnx/zynqmp_dp.c b/drivers/gpu/drm/xlnx/zynqmp_dp.c
index 7fb11b0a44f0..847179476041 100644
--- a/drivers/gpu/drm/xlnx/zynqmp_dp.c
+++ b/drivers/gpu/drm/xlnx/zynqmp_dp.c
@@ -1888,6 +1888,9 @@ static ssize_t zynqmp_dp_pattern_write(struct file *file,
 	ssize_t ret;
 	int pattern;
 
+	if (*ppos != 0)
+		return -EINVAL;
+
 	ret = simple_write_to_buffer(buf, sizeof(buf) - 1, ppos, user_buf,
 				     count);
 	if (ret < 0)
@@ -2028,6 +2031,9 @@ static ssize_t zynqmp_dp_custom_write(struct file *file,
 	ssize_t ret;
 	char buf[sizeof(dp->test.custom)];
 
+	if (*ppos != 0)
+		return -EINVAL;
+
 	ret = simple_write_to_buffer(buf, sizeof(buf), ppos, user_buf, count);
 	if (ret < 0)
 		return ret;
-- 
2.53.0