[PATCH] ALSA: pcmtest: Reject invalid fill_mode values

[HyeongJun An <sammiee5311@gmail.com>]

The fill_block() function handles only fill_mode 0 (random) and 1
(pattern). With any other value it writes nothing and does not move the
buffer position. A capture stream then gets no data, and a read fails
with -EIO after the timeout. Nothing in the kernel log says why.

Check the value in a set callback, so a bad value is rejected both when
the module is loaded and when the parameter is written.

Fixes: 315a3d57c64c ("ALSA: Implement the new Virtual PCM Test Driver")
Assisted-by: Claude:claude-opus-5-5
Signed-off-by: HyeongJun An <sammiee5311@gmail.com>
---
 sound/drivers/pcmtest.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/sound/drivers/pcmtest.c b/sound/drivers/pcmtest.c
index d1b0dff56cd9..422fdb10f237 100644
--- a/sound/drivers/pcmtest.c
+++ b/sound/drivers/pcmtest.c
@@ -72,13 +72,32 @@ static u8 playback_capture_test;
 static u8 ioctl_reset_test;
 static struct dentry *driver_debug_dir;
 
+static int fill_mode_set(const char *val, const struct kernel_param *kp)
+{
+	short mode;
+	int err;
+
+	err = kstrtos16(val, 0, &mode);
+	if (err)
+		return err;
+	if (mode != FILL_MODE_RAND && mode != FILL_MODE_PAT)
+		return -EINVAL;
+	fill_mode = mode;
+	return 0;
+}
+
+static const struct kernel_param_ops fill_mode_ops = {
+	.set = fill_mode_set,
+	.get = param_get_short,
+};
+
 module_param(index, int, 0444);
 MODULE_PARM_DESC(index, "Index value for pcmtest soundcard");
 module_param(id, charp, 0444);
 MODULE_PARM_DESC(id, "ID string for pcmtest soundcard");
 module_param(enable, bool, 0444);
 MODULE_PARM_DESC(enable, "Enable pcmtest soundcard.");
-module_param(fill_mode, short, 0600);
+module_param_cb(fill_mode, &fill_mode_ops, &fill_mode, 0600);
 MODULE_PARM_DESC(fill_mode, "Buffer fill mode: rand(0) or pattern(1)");
 module_param(inject_delay, int, 0600);
 MODULE_PARM_DESC(inject_delay, "Inject delays during playback/capture (in jiffies)");
-- 
2.43.0