ALSA: emu8000: Fix a use after free in snd_emu8000_create_mixer

commit 1c98f574403dbcf2eb832d5535a10d967333ef2d upstream.

Our code analyzer reported a uaf.

In snd_emu8000_create_mixer, the callee snd_ctl_add(..,emu->controls[i])
calls snd_ctl_add_replace(.., kcontrol,..). Inside snd_ctl_add_replace(),
if error happens, kcontrol will be freed by snd_ctl_free_one(kcontrol).
Then emu->controls[i] points to a freed memory, and the execution comes
to __error branch of snd_emu8000_create_mixer. The freed emu->controls[i]
is used in snd_ctl_remove(card, emu->controls[i]).

My patch set emu->controls[i] to NULL if snd_ctl_add() failed to avoid
the uaf.

Signed-off-by: Lv Yunlong <lyl2019@mail.ustc.edu.cn>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20210426131129.4796-1-lyl2019@mail.ustc.edu.cn
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/sound/isa/sb/emu8000.c b/sound/isa/sb/emu8000.c
index d56973b..24b91cb 100644 (file)
--- a/sound/isa/sb/emu8000.c
+++ b/sound/isa/sb/emu8000.c
@@ -1042,8 +1042,10 @@ snd_emu8000_create_mixer(struct snd_card *card, struct snd_emu8000 *emu)
 
        memset(emu->controls, 0, sizeof(emu->controls));
        for (i = 0; i < EMU8000_NUM_CONTROLS; i++) {
-               if ((err = snd_ctl_add(card, emu->controls[i] = snd_ctl_new1(mixer_defs[i], emu))) < 0)
+               if ((err = snd_ctl_add(card, emu->controls[i] = snd_ctl_new1(mixer_defs[i], emu))) < 0) {
+                       emu->controls[i] = NULL;
                        goto __error;
+               }
        }
        return 0;