From: Clement Lecigne clecigne@google.com

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: stable@kernel.org # 5.13+ Signed-off-by: Clement Lecigne clecigne@google.com Signed-off-by: Takashi Iwai tiwai@suse.de ---

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;