At transition to the iov_iter for PCM data transfer, we blindly
applied the iov_iter setup also for silencing (i.e. data = NULL), and
it leads to a calculation of bogus iov_iter.  Fortunately this didn't
cause troubles on most of architectures but it goes wrong on RISC-V
now, causing a NULL dereference.

Handle the NULL data case to treat the silencing in interleaved_copy()
for addressing the bug above.  noninterleaved_copy() has already the
NULL data handling, so it doesn't need changes.

Reported-by: Jiakai Xu <xujiakai24@mails.ucas.ac.cn>
Closes: https://lore.kernel.org/20260515051516.3103036-1-xujiakai24@mails.ucas.ac.cn
Fixes: cf393babb37a ("ALSA: pcm: Add copy ops with iov_iter")
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
 sound/core/pcm_lib.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
index 09c421cd9319..fe597f7d522d 100644
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -2138,6 +2138,9 @@ static int interleaved_copy(struct snd_pcm_substream *substream,
 	off = frames_to_bytes(runtime, off);
 	frames = frames_to_bytes(runtime, frames);
 
+	if (!data)
+		return fill_silence(substream, 0, hwoff, NULL, frames);
+
 	return do_transfer(substream, 0, hwoff, data + off, frames, transfer,
 			   in_kernel);
 }
-- 
2.54.0