ALSA: control: Don't access controls outside of protected regions

A control that is visible on the card->controls list can be freed at any time.
This means we must not access any of its memory while not holding the
controls_rw_lock. Otherwise we risk a use after free access.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Jaroslav Kysela <perex@perex.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 10 insertions, 5 deletions

diff --git a/sound/core/control.c b/sound/core/control.c
index 1f413c286511..5c49f976fc7b 100644
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -330,6 +330,7 @@ int snd_ctl_add(struct snd_card *card, struct snd_kcontrol *kcontrol)
 {
         struct snd_ctl_elem_id id;
         unsigned int idx;
+        unsigned int count;
         int err = -EINVAL;
 
         if (! kcontrol)
@@ -358,8 +359,9 @@ int snd_ctl_add(struct snd_card *card, struct snd_kcontrol *kcontrol)
         card->controls_count += kcontrol->count;
         kcontrol->id.numid = card->last_numid + 1;
         card->last_numid += kcontrol->count;
+        count = kcontrol->count;
         up_write(&card->controls_rwsem);
-        for (idx = 0; idx < kcontrol->count; idx++, id.index++, id.numid++)
+        for (idx = 0; idx < count; idx++, id.index++, id.numid++)
                 snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_ADD, &id);
         return 0;
 
@@ -388,6 +390,7 @@ int snd_ctl_replace(struct snd_card *card, struct snd_kcontrol *kcontrol,
                     bool add_on_replace)
 {
         struct snd_ctl_elem_id id;
+        unsigned int count;
         unsigned int idx;
         struct snd_kcontrol *old;
         int ret;
@@ -423,8 +426,9 @@ add:
         card->controls_count += kcontrol->count;
         kcontrol->id.numid = card->last_numid + 1;
         card->last_numid += kcontrol->count;
+        count = kcontrol->count;
         up_write(&card->controls_rwsem);
-        for (idx = 0; idx < kcontrol->count; idx++, id.index++, id.numid++)
+        for (idx = 0; idx < count; idx++, id.index++, id.numid++)
                 snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_ADD, &id);
         return 0;
 
@@ -897,9 +901,9 @@ static int snd_ctl_elem_write(struct snd_card *card, struct snd_ctl_file *file,
                         result = kctl->put(kctl, control);
                 }
                 if (result > 0) {
+                        struct snd_ctl_elem_id id = control->id;
                         up_read(&card->controls_rwsem);
-                        snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_VALUE,
-                                       &control->id);
+                        snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_VALUE, &id);
                         return 0;
                 }
         }
@@ -1333,8 +1337,9 @@ static int snd_ctl_tlv_ioctl(struct snd_ctl_file *file,
                 }
                 err = kctl->tlv.c(kctl, op_flag, tlv.length, _tlv->tlv);
                 if (err > 0) {
+                        struct snd_ctl_elem_id id = kctl->id;
                         up_read(&card->controls_rwsem);
-                        snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_TLV, &kctl->id);
+                        snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_TLV, &id);
                         return 0;
                 }
         } else {