[PATCH] ALSA: control: do not access controls without possession of r_w lock

[Ma Ke]

we should not access any of its memory when we don't ensure possession of
a read/write lock. Otherwise we risk a use after free access, which allows
local users to cause a denial of service and obtain sensitive information
from kernel memory.

Signed-off-by: Ma Ke <make_ruc2021@xxxxxxx>
---
 sound/core/control.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/sound/core/control.c b/sound/core/control.c
index 59c8658966d4..98782cc68ee1 100644
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -590,7 +590,8 @@ static int __snd_ctl_remove(struct snd_card *card,
 		remove_hash_entries(card, kcontrol);
 
 	card->controls_count -= kcontrol->count;
-	for (idx = 0; idx < kcontrol->count; idx++)
+	count = kcontrol->count;
+	for (idx = 0; idx < count; idx++)
 		snd_ctl_notify_one(card, SNDRV_CTL_EVENT_MASK_REMOVE, kcontrol, idx);
 	snd_ctl_free_one(kcontrol);
 	return 0;
-- 
2.37.2