2021-04-26 14:56:47

by Lv Yunlong

Subject: [PATCH] sound/isa/ib: Fix two use after free in snd_sb_qsound_build

In snd_sb_qsound_build, snd_ctl_add(..,p->qsound_switch...) and
snd_ctl_add(..,p->qsound_space..) are called. But the second
arguments of snd_ctl_add() could be freed via snd_ctl_add_replace()
->snd_ctl_free_one(). After the error code is returned,
snd_sb_qsound_destroy(p) is called in __error branch.

But in snd_sb_qsound_destroy(), the freed p->qsound_switch and
p->qsound_space are still used by snd_ctl_remove().

My patch set p->qsound_switch and p->qsound_space to NULL if
snd_ctl_add() failed to avoid the uaf bugs. But these codes need
to further be improved with the code style.

Signed-off-by: Lv Yunlong <[email protected]>
---
sound/isa/sb/sb16_csp.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/sound/isa/sb/sb16_csp.c b/sound/isa/sb/sb16_csp.c
index 8635a2b6b36b..4789345a8fdd 100644
--- a/sound/isa/sb/sb16_csp.c
+++ b/sound/isa/sb/sb16_csp.c
@@ -1045,10 +1045,14 @@ static int snd_sb_qsound_build(struct snd_sb_csp * p)

spin_lock_init(&p->q_lock);

- if ((err = snd_ctl_add(card, p->qsound_switch = snd_ctl_new1(&snd_sb_qsound_switch, p))) < 0)
+ if ((err = snd_ctl_add(card, p->qsound_switch = snd_ctl_new1(&snd_sb_qsound_switch, p))) < 0) {
+ p->qsound_switch = NULL;
goto __error;
- if ((err = snd_ctl_add(card, p->qsound_space = snd_ctl_new1(&snd_sb_qsound_space, p))) < 0)
+ }
+ if ((err = snd_ctl_add(card, p->qsound_space = snd_ctl_new1(&snd_sb_qsound_space, p))) < 0) {
+ p->qsound_space = NULL;
goto __error;
+ }

return 0;

--
2.25.1

2021-04-26 16:02:32

by Takashi Iwai

Subject: Re: [PATCH] sound/isa/ib: Fix two use after free in snd_sb_qsound_build

On Mon, 26 Apr 2021 16:55:41 +0200,
Lv Yunlong wrote:
>
> In snd_sb_qsound_build, snd_ctl_add(..,p->qsound_switch...) and
> snd_ctl_add(..,p->qsound_space..) are called. But the second
> arguments of snd_ctl_add() could be freed via snd_ctl_add_replace()
> ->snd_ctl_free_one(). After the error code is returned,
> snd_sb_qsound_destroy(p) is called in __error branch.
>
> But in snd_sb_qsound_destroy(), the freed p->qsound_switch and
> p->qsound_space are still used by snd_ctl_remove().
>
> My patch set p->qsound_switch and p->qsound_space to NULL if
> snd_ctl_add() failed to avoid the uaf bugs. But these codes need
> to further be improved with the code style.
>
> Signed-off-by: Lv Yunlong <[email protected]>

Thanks, applied now.


Takashi