[PATCH 4.9 048/240] ALSA: emu8000: Fix a use after free in snd_emu8000_create_mixer

Greg Kroah-Hartman
2021-05-20T11:05:32Z

From: Lv Yunlong <lyl2019@mail.ustc.edu.cn>

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>
---
sound/isa/sb/emu8000.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

--- a/sound/isa/sb/emu8000.c
+++ b/sound/isa/sb/emu8000.c
@@ -1042,8 +1042,10 @@ snd_emu8000_create_mixer(struct snd_card

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;