[PATCH 6.18.y 2/2] ALSA: timer: Handle userspace-driven timer ioctls from 32-bit tasks

[Sasha Levin <sashal@kernel.org>]

From: Danish Khateeb <danishkhateeb03@gmail.com>

[ Upstream commit 1bbc033983b76f41d51d4a48838bf94c5e6b6f50 ]

32-bit tasks on a 64-bit kernel can't use userspace-driven timers. The
compat handler for /dev/snd/timer doesn't list SNDRV_TIMER_IOCTL_CREATE,
so creating a timer fails with -ENOTTY. The file returned for a timer
has no .compat_ioctl either, so SNDRV_TIMER_IOCTL_TRIGGER fails with
-ENOTTY too.

struct snd_timer_uinfo has the same layout for 32-bit and 64-bit tasks,
and SNDRV_TIMER_IOCTL_TRIGGER takes no argument, so both commands can
be passed through unchanged.

The utimer selftest doesn't catch this when built with -m32: it takes
-ENOTTY from SNDRV_TIMER_IOCTL_CREATE to mean CONFIG_SND_UTIMER=n and
skips.

Fixes: 37745918e0e7 ("ALSA: timer: Introduce virtual userspace-driven timers")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Danish Khateeb <danishkhateeb03@gmail.com>
Link: https://patch.msgid.link/20260928182352.309457-1-danishkhateeb03@gmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 sound/core/timer.c        | 1 +
 sound/core/timer_compat.c | 1 +
 2 files changed, 2 insertions(+)

diff --git a/sound/core/timer.c b/sound/core/timer.c
index 9838cc6636427..64bffc21295d4 100644
--- a/sound/core/timer.c
+++ b/sound/core/timer.c
@@ -2104,6 +2104,7 @@ static const struct file_operations snd_utimer_fops = {
 	.llseek		=	noop_llseek,
 	.release	=	snd_utimer_release,
 	.unlocked_ioctl	=	snd_utimer_ioctl,
+	.compat_ioctl	=	snd_utimer_ioctl,
 };
 
 static int snd_utimer_start(struct snd_timer *t)
diff --git a/sound/core/timer_compat.c b/sound/core/timer_compat.c
index 4ae9eaeb5afb1..7b648edcb9cba 100644
--- a/sound/core/timer_compat.c
+++ b/sound/core/timer_compat.c
@@ -98,6 +98,7 @@ static long __snd_timer_user_ioctl_compat(struct file *file, unsigned int cmd,
 	case SNDRV_TIMER_IOCTL_PAUSE:
 	case SNDRV_TIMER_IOCTL_PAUSE_OLD:
 	case SNDRV_TIMER_IOCTL_NEXT_DEVICE:
+	case SNDRV_TIMER_IOCTL_CREATE:
 		return __snd_timer_user_ioctl(file, cmd, (unsigned long)argp, true);
 	case SNDRV_TIMER_IOCTL_GPARAMS32:
 		return snd_timer_user_gparams_compat(file, argp);
-- 
2.53.0