2023-01-13 12:32:51

by Takashi Iwai

Subject: [PATCH] ALSA: pcm: Move rwsem lock inside snd_ctl_elem_read to prevent UAF

From: Clement Lecigne <[email protected]>

Takes rwsem lock inside snd_ctl_elem_read instead of snd_ctl_elem_read_user
like it was done for write in commit 1fa4445f9adf1 ("ALSA: control - introduce
snd_ctl_notify_one() helper"). Doing this way we are also fixing the following
locking issue happening in the compat path which can be easily triggered and
turned into an use-after-free.

64-bits:
snd_ctl_ioctl
snd_ctl_elem_read_user
[takes controls_rwsem]
snd_ctl_elem_read [lock properly held, all good]
[drops controls_rwsem]

32-bits:
snd_ctl_ioctl_compat
snd_ctl_elem_write_read_compat
ctl_elem_write_read
snd_ctl_elem_read [missing lock, not good]

CVE-2023-0266 was assigned for this issue.

Cc: [email protected] # 5.13+
Signed-off-by: Clement Lecigne <[email protected]>
Signed-off-by: Takashi Iwai <[email protected]>
---

Note: the fixes for older stable trees will be submitted in another patch

sound/core/control.c | 24 +++++++++++++++---------
1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/sound/core/control.c b/sound/core/control.c
index 50e7ba66f187..82aa1af1d1d8 100644
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -1203,14 +1203,19 @@ static int snd_ctl_elem_read(struct snd_card *card,
const u32 pattern = 0xdeadbeef;
int ret;

+ down_read(&card->controls_rwsem);
kctl = snd_ctl_find_id(card, &control->id);
- if (kctl == NULL)
- return -ENOENT;
+ if (kctl == NULL) {
+ ret = -ENOENT;
+ goto unlock;
+ }

index_offset = snd_ctl_get_ioff(kctl, &control->id);
vd = &kctl->vd[index_offset];
- if (!(vd->access & SNDRV_CTL_ELEM_ACCESS_READ) || kctl->get == NULL)
- return -EPERM;
+ if (!(vd->access & SNDRV_CTL_ELEM_ACCESS_READ) || kctl->get == NULL) {
+ ret = -EPERM;
+ goto unlock;
+ }

snd_ctl_build_ioff(&control->id, kctl, index_offset);

@@ -1220,7 +1225,7 @@ static int snd_ctl_elem_read(struct snd_card *card,
info.id = control->id;
ret = __snd_ctl_elem_info(card, kctl, &info, NULL);
if (ret < 0)
- return ret;
+ goto unlock;
#endif

if (!snd_ctl_skip_validation(&info))
@@ -1230,7 +1235,7 @@ static int snd_ctl_elem_read(struct snd_card *card,
ret = kctl->get(kctl, control);
snd_power_unref(card);
if (ret < 0)
- return ret;
+ goto unlock;
if (!snd_ctl_skip_validation(&info) &&
sanity_check_elem_value(card, control, &info, pattern) < 0) {
dev_err(card->dev,
@@ -1238,8 +1243,11 @@ static int snd_ctl_elem_read(struct snd_card *card,
control->id.iface, control->id.device,
control->id.subdevice, control->id.name,
control->id.index);
- return -EINVAL;
+ ret = -EINVAL;
+ goto unlock;
}
+unlock:
+ up_read(&card->controls_rwsem);
return ret;
}

@@ -1253,9 +1261,7 @@ static int snd_ctl_elem_read_user(struct snd_card *card,
if (IS_ERR(control))
return PTR_ERR(control);

- down_read(&card->controls_rwsem);
result = snd_ctl_elem_read(card, control);
- up_read(&card->controls_rwsem);
if (result < 0)
goto error;

--
2.35.3

2023-01-13 14:16:43

by Jaroslav Kysela

Subject: Re: [PATCH] ALSA: pcm: Move rwsem lock inside snd_ctl_elem_read to prevent UAF

On 13. 01. 23 13:07, Takashi Iwai wrote:
> From: Clement Lecigne <[email protected]>
>
> Takes rwsem lock inside snd_ctl_elem_read instead of snd_ctl_elem_read_user
> like it was done for write in commit 1fa4445f9adf1 ("ALSA: control - introduce
> snd_ctl_notify_one() helper"). Doing this way we are also fixing the following
> locking issue happening in the compat path which can be easily triggered and
> turned into an use-after-free.
>
> 64-bits:
> snd_ctl_ioctl
> snd_ctl_elem_read_user
> [takes controls_rwsem]
> snd_ctl_elem_read [lock properly held, all good]
> [drops controls_rwsem]
>
> 32-bits:
> snd_ctl_ioctl_compat
> snd_ctl_elem_write_read_compat
> ctl_elem_write_read
> snd_ctl_elem_read [missing lock, not good]
>
> CVE-2023-0266 was assigned for this issue.
>
> Cc: [email protected] # 5.13+
> Signed-off-by: Clement Lecigne <[email protected]>
> Signed-off-by: Takashi Iwai <[email protected]>

Reviewed-by: Jaroslav Kysela <[email protected]>

--
Jaroslav Kysela <[email protected]>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.