ALSA: sb: Fix potential double-free of CSP mixer elements

snd_sb_qsound_destroy() contains the calls of removing the previously
created mixer controls, but it doesn't clear the pointers.  As
snd_sb_qsound_destroy() itself may be repeatedly called via ioctl,
this could lead to double-free potentially.

Fix it by clearing the struct fields properly afterwards.

Link: https://lore.kernel.org/r/20210608140540.17885-4-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/isa/sb/sb16_csp.c b/sound/isa/sb/sb16_csp.c
index dec68ae..5bbe669 100644 (file)
--- a/sound/isa/sb/sb16_csp.c
+++ b/sound/isa/sb/sb16_csp.c
@@ -1077,10 +1077,14 @@ static void snd_sb_qsound_destroy(struct snd_sb_csp * p)
        card = p->chip->card;   
        
        down_write(&card->controls_rwsem);
-       if (p->qsound_switch)
+       if (p->qsound_switch) {
                snd_ctl_remove(card, p->qsound_switch);
-       if (p->qsound_space)
+               p->qsound_switch = NULL;
+       }
+       if (p->qsound_space) {
                snd_ctl_remove(card, p->qsound_space);
+               p->qsound_space = NULL;
+       }
        up_write(&card->controls_rwsem);
 
        /* cancel pending transfer of QSound parameters */